Structures Inspection Manual Part 2: Deterioration Mechanisms

Manual
Structures Inspection Manual

Part 2: Deterioration Mechanisms
September 2016
Copyright
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© State of Queensland (Department of Transport and Main Roads) 2016
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Structures Inspection Manual, Transport and Main Roads, September 2016

Contents
1 Introduction ....................................................................................................................................1
2 Material defects ..............................................................................................................................1
2.1 General ........................................................................................................................................... 1
2.2 Concrete ......................................................................................................................................... 1
2.2.1 Corrosion of reinforcement .............................................................................................2
2.2.2 Alkali-Aggregate Reaction (AAR) ...................................................................................4
2.2.3 Cracking .........................................................................................................................6
2.2.4 Spalling ........................................................................................................................ 10
2.2.5 Delamination ................................................................................................................ 11
2.2.6 Surface defects............................................................................................................ 12
2.2.7 Scaling ......................................................................................................................... 13
2.2.8 Disintegration............................................................................................................... 14
2.2.9 Fire .............................................................................................................................. 14
2.3 Steel .............................................................................................................................................. 15
2.3.1 Corrosion ..................................................................................................................... 15
2.3.2 Protective coating systems .......................................................................................... 17
2.3.3 Permanent deformations ............................................................................................. 19
2.3.4 Cracking ...................................................................................................................... 20
2.3.5 Loose connections....................................................................................................... 23
2.3.6 Fire damage ................................................................................................................ 24
2.3.7 Impact damage ............................................................................................................ 24
2.4 Timber ........................................................................................................................................... 24
2.4.1 Fungi ............................................................................................................................ 24
2.4.2 Termites ....................................................................................................................... 25
2.4.3 Marine organisms ........................................................................................................ 27
2.4.4 Corrosion of fasteners ................................................................................................. 28
2.4.5 Fire .............................................................................................................................. 29
2.4.6 Weathering .................................................................................................................. 30
2.4.7 Floods .......................................................................................................................... 30
2.5 Masonry ........................................................................................................................................ 30
2.5.1 Cracking ...................................................................................................................... 31
2.5.2 Splitting, spalling and disintegration ............................................................................ 31
2.5.3 Loss of mortar and stones ........................................................................................... 31
2.5.4 Arch stones dropping .................................................................................................. 31
2.5.5 Deformation ................................................................................................................. 31
2.6 Fibre Reinforced Polymers (FRP)................................................................................................. 32
2.6.1 FRP strengthening....................................................................................................... 32
2.6.2 FRP components ......................................................................................................... 32
3 Common defects observed in existing structures .................................................................. 34
3.1 Concrete bridges .......................................................................................................................... 34
3.1.1 Monolithic and simply-supported T-beams ................................................................. 34
3.1.2 Precast ‘I’ beams ......................................................................................................... 34
3.1.3 Precast prestressed inverted ‘T’ beams ...................................................................... 34
3.1.4 Box girder bridges ....................................................................................................... 35
3.1.5 Prestressed voided flat slab bridges ........................................................................... 35
3.1.6 Reinforced concrete flat slabs ..................................................................................... 35
3.1.7 Precast prestressed deck units ................................................................................... 35
3.1.8 Precast prestressed voided ‘T’ beams ........................................................................ 36
3.1.9 Decks and overlays ..................................................................................................... 36
3.1.10 Diaphragms ................................................................................................................. 36
3.1.11 Kerbs, footways, posts and railing............................................................................... 37
3.1.12 Abutments ................................................................................................................... 37
Structures Inspection Manual, Transport and Main Roads, September 2016 i

3.1.13 Piers ............................................................................................................................ 38
3.2 Steel bridges ................................................................................................................................. 39
3.3 Timber bridges .............................................................................................................................. 39
3.3.1 Timber girders ............................................................................................................. 39
3.3.2 Corbels ........................................................................................................................ 40
3.3.3 Decking (timber and steel trough) ............................................................................... 40
3.3.4 Kerbs, posts and railing ............................................................................................... 43
3.3.5 Piles ............................................................................................................................. 43
3.3.6 Waling’s and crossbraces ........................................................................................... 45
3.3.7 Headstocks .................................................................................................................. 45
3.3.8 Abutments and piers.................................................................................................... 45
3.4 Other structure types .................................................................................................................... 46
3.4.1 Box culverts ................................................................................................................. 46
3.4.2 Pipe culverts ................................................................................................................ 47
3.4.3 Large traffic management signs .................................................................................. 49
3.4.4 Retaining walls ............................................................................................................ 50
3.5 Causes of deterioration not related to construction materials ...................................................... 51
3.5.2 Bearings ...................................................................................................................... 52
3.5.3 Damage due to accidents ............................................................................................ 53
3.5.4 Drainage ...................................................................................................................... 53
3.5.5 Debris .......................................................................................................................... 54
3.5.6 Vegetation ................................................................................................................... 54
3.5.7 Waterway scour ........................................................................................................... 54
3.5.8 Movement of the structure ........................................................................................... 56
3.5.9 Condition of approaches ............................................................................................. 56
4 References ................................................................................................................................... 57
Figures
Figure 2.2.2a – Example ASR crack pattern in pier column ................................................................... 5
Figure 2.2.2b – Example ASR crack pattern in abutment wall ................................................................ 5
Figure 2.2.2c – Example ASR crack pattern in pier headstock ............................................................... 5
Figure 2.2.2d – Example ASR crack pattern in prestressed deck unit soffit ........................................... 5
Figure 2.2.3.1b – Plastic shrinkage cracking in bridge deck ................................................................... 8
Figure 2.2.3.1c – Plastic settlement crack in slab ................................................................................... 8
Figure 2.2.3.2a – Bursting cracks in under-reinforced anchorage zone of post-tensioned girder .......... 9
Figure 2.2.3.2b – Typical flexural cracks at mid-span of girder............................................................... 9
Figure 2.2.3.2c – Crack/separation in abutment wall due to differential settlement................................ 9
Figure 2.2.3.2d – Shear crack in girder adjacent to support ................................................................... 9
Figure 2.2.3.3 – Accurate measurement of crack width ........................................................................ 10
Figure 2.2.4a – Spalling of concrete at ends of deck units ................................................................... 11
Figure 2.2.4b – Spalling to front face of headstock ............................................................................... 11
Figure 2.2.4c – Spalling of slab soffit .................................................................................................... 11
Figure 2.2.4d – Corner spalling of square pile ...................................................................................... 11
Structures Inspection Manual, Transport and Main Roads, September 2016 ii

Figure 2.2.6c – Efflorescence evident on concrete headstock.............................................................. 13
Figure 2.2.6d – Discharge through cracks in concrete surface ............................................................. 13
Figure 2.2.6e – Concrete honeycombing .............................................................................................. 13
Figure 2.2.6f – Abrasion of concrete ..................................................................................................... 13
Figure 2.2.7a – Concrete scaling .......................................................................................................... 14
Figure 2.2.7b – Concrete disintegration ................................................................................................ 14
Figure 2.3.1a – Mild surface corrosion .................................................................................................. 16
Figure 2.3.1b – Severe corrosion and loss of section ........................................................................... 16
Figure 2.3.1c – Pitting of steel ............................................................................................................... 17
Figure 2.3.1d – Corrosion of steel by SRB ............................................................................................ 17
Figure 2.3.2a – White deposit on zinc metal spray ............................................................................... 18
Figure 2.3.2b – Failure of paint system over galvanising ...................................................................... 18
Figure 2.3.2c – Blistering of paint system ............................................................................................. 18
Figure 2.3.2d – Flaking of paint system ................................................................................................ 18
Figure 2.3.3a – Buckling of gusset plate ............................................................................................... 20
Figure 2.3.3b – Impact damage to steel beam ...................................................................................... 20
Figure 2.3.4a – Fatigue cracking in web ............................................................................................... 21
Figure 2.3.4b – Cracking in welds ......................................................................................................... 21
Figure 2.4.1a – Fungal fruiting body and decay of girder ...................................................................... 25
Figure 2.4.1b – Decay pocket in girder ................................................................................................. 25
Figure 2.4.2a – Termite nest on bridge pile........................................................................................... 26
Figure 2.4.2b – Termite gallery on pier headstock ................................................................................ 26
Figure 2.4.3a – External damage to timber pile from shipworm............................................................ 28
Figure 2.4.3b – Timber piles subject to Sphaemora attack ................................................................... 28
Figure 2.4.4.1a – Splitting in timber pile ................................................................................................ 29
Figure 2.4.4.1b – Splitting in timber headstock ..................................................................................... 29
Figure 3.3.3.2a – Abrasion of wearing surface...................................................................................... 42
Figure 3.3.3.2b – Failure of plywood deck panel .................................................................................. 42
Figure 3.3.3.4a – Corrosion of joints between trough sections ............................................................. 43
Figure 3.3.3.4b – Cracking and perforation of steel trough decking ..................................................... 43
Figure 3.3.5a – Decay of pile below ground level ................................................................................. 44
Figure 3.3.5b – Splitting of pile beneath headstock .............................................................................. 44
Figure 3.4.2.1a – Cracking of pipe walls ............................................................................................... 48
Structures Inspection Manual, Transport and Main Roads, September 2016 iii
Figure 3.4.2.1b – Loss of cover/spalling concrete in pipe crown .......................................................... 48
Figure 3.4.2.2a – Typical location of wall corrosion in BCM culvert ...................................................... 48
Figure 3.4.2.2b – BCM culvert wall corrosion above invert protection .................................................. 48
Figure 3.5.7a – Example of recent bank erosion .................................................................................. 55
Figure 3.5.7b – Localised scour around pier pile cap and piles ............................................................ 55
Figure 3.5.7c – Localised scour around pier piles and debris build-up ................................................. 55
Figure 3.5.7d – Settlement of rigid batter protection ............................................................................. 55
Structures Inspection Manual, Transport and Main Roads, September 2016 iv

1 Introduction
The intent of any structure inspection is to identify and record the presence of defects. While diagnosis
of the causes of defects is not a requirement for a Level `1 or Level 2 inspection, it is of great value for
the inspector to have an appreciation of structural behaviour and of the defects that might occur.
Such an appreciation will guide and alert the inspector to particular signs enabling attention to be
focussed where it is most needed. This ensures that, when a defect is observed, the necessary data is
collected on site so that a correct diagnosis can be made, especially when defects occur due to a
combination of causes.
Identification of structural defects and their causes require considerable care as structural distress
within an element may often have consequential effects on other elements and it may not be
immediately apparent which element has caused the failure. For example:
• Failure in the bridge foundations, due to settlement, sliding or rotation, is often manifested as
cracking, differential movement or other defect in the substructure. Such movements may be
displayed as abnormal clearances between the abutment ballast wall and the end of the deck,
or as out-of-range movements at the expansion joints or bearings.
• Settlement of embankments may affect the substructure, appearing as depressions in the

road surface adjacent to the structure or as discontinuities in the kerb line.
• Seized or locked bearings can transfer unexpected forces into the bearing shelf resulting in
spalling to the front face of the headstock or bearing shelf.
This document is intended as a guide to some of the more common material and structure related
defects likely to be encountered on the network.
2 Material defects
2.1 General
This section describes the defects that are normally found in concrete, steel, timber, masonry and
coatings. Each defect is briefly described and the causes producing it are identified.
2.2 Concrete
Based on concrete defects described in Ontario Ministry of Transportation, Ontario Structure

Inspection Manual and adjusted for Queensland conditions.
Concrete is used in structures as plain concrete, such as tremie and mass concrete; or it is combined
with conventional steel reinforcement as reinforced concrete, or with prestressing steel reinforcement
as prestressed concrete.
Defects in concrete can often be related to the lack of durability of the concrete, resulting from the
composition of the concrete, poor placement practices, poor quality control or the aggressive
environment in which it is placed.
The following defects which have occurred in the Queensland road infrastructure are described. They
have been listed in order of occurrence from most common to least as found in our concrete road
bridges to date:
i. Corrosion of reinforcement
ii. Carbonation1
Structures Inspection Manual, Transport and Main Roads, September 2016 1

iii. Alkali-aggregate Reaction(AAR)2
iv. Cracking
v. Spalling
vi. Surface defects
vii. Delamination
viii. Scaling
ix. Disintegration
x. Chloride ingress1
xi. Water wash.

1These phenomena cause the conditions for corrosion (and ultimately cracking, spalling and delamination) to
occur.
2 This phenomena results in cracking of concrete and also promotes other deterioration mechanisms.
2.2.1 Corrosion of reinforcement
Corrosion is a consequence of the deterioration of reinforcement by electrolysis.
Reinforcement is usually protected by a passive film which forms due to the alkaline environment of
concrete. Corrosion will not normally occur in most concrete elements unless the passive layer breaks
down. This will typically only occur if the alkalinity of the concrete is reduced (through carbonation) or
where sufficiently high concentrations of chloride in the concrete causes local break down of the
passive layer.
Figure 2.2.1a – Stages of reinforcement corrosion

In the initial stages, corrosion may appear as rust staining on the concrete surface. In the advanced
stages, the cover concrete above the reinforcement cracks, delaminates and spalls off exposing
heavily corroded reinforcement. This process is illustrated in Figure 2.2.1a.
Figure 2.2.1b illustrates types of damage sustained by concrete structures when embedded steel
corrodes.
Figure 2.2.1b – Concrete defects resulting from reinforcement corrosion
In Queensland, the most common example of damage resulting from reinforcement corrosion is found
in the square section reinforced concrete piles which were used extensively until the introduction of
prestressed octagonal piles. Cracking typically follows the line of the corner reinforcement where two
concrete faces are exposed to the environment (increasing the rate of carbonation and/or chloride
ingress) and the density of the concrete is compromised by limited access for compaction. The
severity of the cracking increases until the cover concrete delaminates and ultimately spalls off
exposing the corroded reinforcement. In addition horizontal cracking caused by driving stresses is
often found in this type of pile.
2.2.1.1 Carbonation
Carbonation is the process by which carbon dioxide in the atmosphere dissolves in moisture within the
concrete pores and reacts with calcium hydroxide present in the cement paste. This forms a neutral
calcium carbonate which, over a long period of time gradually lowers the alkalinity of the concrete
cover to the steel reinforcement, breaking down the protective passive film around the embedded
steel.

The depth of carbonation from the exterior surface can be estimated by using a pH indicator, e.g.
phenolphthalein dissolved in water. When the indicator is applied to a freshly exposed concrete
surface the carbonated zone remains clear while the uncarbonated area turns pink (Figure 2.2.1.1).
Figure 2.2.1.1 – Example use of phenolphthalein indicator
As stated above, carbonation only provides an environment for corrosion to occur (i.e. by breaking
down the passive protective layer) and does not, in itself, constitute a defect.
2.2.1.2 Chloride ingress
Chloride ions can initiate corrosion in embedded steel even at high alkanities (i.e. before the process
of carbonation has reduced alkaline levels to the point where the passive protective layer around
embedded steel has broken down).
The primary source for these ions to enter the concrete in Queensland is through contact with salt
spray and/or salt-laden water. In coastal areas and river estuaries tidal flows can bring salt-laden
water inland and/or strong winds may blow salt spray several kilometres inland.
Other sources include the introduction of chloride during concrete production through contaminated
water or admixtures.
2.2.2 Alkali-Aggregate Reaction (AAR)
Two types of alkali-aggregate reaction are currently recognised depending on the nature of the
reactive mineral. These are:
• Alkali-Silica Reaction (ASR) – involves various types of reactive silica.
• Alkali-Carbonate Reaction (ACR) – involves certain types of dolomitic rocks.
The reactive mineral present in aggregates react adversely with alkalis in the cement paste to produce
hydrophilic gel within the pores of the concrete matrix. When the gel is exposed to moisture it
expands, resulting in expansive forces being exerted on the concrete with associated deterioration in
the form of cracking and spalling. The cracking occurs through the entire mass of the concrete and

can take the form of extensive map cracking and/or cracking aligned with the major stress direction or
reinforcement. White or colourless exudations around some of the cracks are also an indicator that
AAR may be occurring. The appearance of concrete components affected by AAR is shown in
Figure 2.2.2a – Figure 2.2.2d.
Alkali-aggregate reactions are generally slow by nature, and the results may not be apparent for 5 to
10 years.
It’s important to note that water is required for the expansive process and, if this can be controlled, the
effects of AAR can usually be managed.
Once AAR cracking presents, clearly it renders the concrete more vulnerable to deterioration through
other processes (e.g. corrosion) by compromising the cover concrete.
ASR cracking most commonly occurs in prestressed deck units in Queensland (Figure 2.2.2d).
Vertical cracking has also been detected in some prestressed octagonal piles which is the result of
Alkali-Silica Reaction (ASR). The risk of this type of cracking has been minimised in new construction
by the use of an appropriate mass of fly ash in the approved mix designs.
Figure 2.2.2a – Example ASR crack pattern in pier Figure 2.2.2b – Example ASR crack pattern in
column abutment wall
Figure 2.2.2c – Example ASR crack pattern in pier Figure 2.2.2d – Example ASR crack pattern in
headstock prestressed deck unit soffit

2.2.3 Cracking
A crack is a linear fracture in concrete which extends partly or completely through the member. Cracks
in concrete occur due to tensile stresses introduced in the concrete as a result of volumetric changes
or applied loads.
Tensile stresses are initially carried by the concrete and reinforcement until the level of the tensile
stress exceeds the tensile capacity of the concrete. After this point the concrete cracks and the tensile
force is transferred completely to the steel reinforcement. In reinforced and prestressed concrete,
crack widths and their distribution are controlled by the reinforcing steel, whereas in plain concrete
there is no such control.
The build-up of tensile stresses and, therefore, cracks in the concrete may be due to any number of
causes and occur at different stages of the concrete development. Figure 2.2.3 summarises the
possible crack types and the stages at which they may develop (plastic state and after hardening).
Figure 2.2.3.1a illustrates typical crack patterns and locations.
Figure 2.2.3 – Types of cracking in concrete
2.2.3.1 Plastic cracking
Plastic cracking of concrete occurs either as plastic settlement cracking or as plastic shrinkage
cracking. Plastic settlement cracking typically occurs in columns, beams or walls, whilst plastic

shrinkage cracks occur most commonly in freshly placed flat exposed slabs. Settlement induced
cracking can also occur in non-vibrated slabs.
Both plastic and settlement cracking are associated with bleeding of fresh concrete, i.e. water rising to
the top of the concrete shortly after compaction. It is caused by the gravitational pull on heavy solid
particles in fresh concrete and the displacement of the lighter water upwards which causes bleeding.
Figure 2.2.3.1a – Classification of cracks in concrete structures
Plastic shrinkage cracks (refer Figure 2.2.3.1b) are typically short and random, forming a map pattern
(crazing), a series of parallel lines or over reinforcement. These cracks, together with those resulting
from thermal effects (in the plastic state) are typically shallow and are dormant. However, if a slab is
significantly affected by plastic shrinkage cracking the cracks may continue through the depth of the
slab.
Plastic settlement cracks (refer Figure 2.2.3.1c) occur opposite rigidly supported reinforcement or
other embedded items. They may also occur at pronounced changes in section depth. They present
as cracks following the direction of reinforcement on the tops of deep beams and slabs or stirrups in
columns. The cracks can be wide at the surface but are rarely deep enough to affect the structural
integrity.

Figure 2.2.3.1b – Plastic shrinkage cracking in Figure 2.2.3.1c – Plastic settlement crack in slab
bridge deck
2.2.3.2 Cracking of hardened concrete
Common causes of cracking in hardened concrete are:
• Drying shrinkage – essentially the contraction that occurs when fresh concrete rapidly dries.
Concrete tends to shrink whenever its surfaces are exposed to air of relatively low humidity.
Drying shrinkage cracks can present as longitudinal cracks (in the case of thin slabs and
walls) or as a network of very fine, closely spaced random cracks (surface crazing).
• Steel corrosion – discussed in paragraph 2.2.1.
• Alkali-aggregate reactions – discussed in paragraph 2.2.2.
• Externally applied loads – these generate a system of internal compressive and tensile
stresses, in the members and components of the structure, as required to maintain static
equilibrium. For example, prestressing generates bursting effects at anchorage zones which
will cause tensile cracks if the member is inadequately reinforced as shown in Figure 2.2.3.2a.
Cracks resulting from externally applied loads initially appear as hairline cracks and are
harmless. However as the reinforcement is further stressed the initial cracks open up and
progressively spread into wider cracks (refer to Figure 2.2.3.2b and Figure 2.2.3.2c). Of
particular concern is the development of shear cracks in structural members adjacent to
supports which may be indicative of incipient brittle failure as shown in Figure 2.2.3.2d.
• External restraint forces - are generated if the free movement of the concrete in response to
the effects of temperature, creep and shrinkage is prevented from occurring due to restraint at
the member supports. The restraint may consist of friction at the bearings, bonding to already
hardened concrete, or by attachment to other components of the structure. Cracks resulting
from the actions of external restraint forces develop in a similar manner as those due to
externally applied loads.

Figure 2.2.3.2a – Bursting cracks in under- Figure 2.2.3.2b – Typical flexural cracks at mid-
reinforced anchorage zone of post-tensioned span of girder
girder
• Differential movement/settlement - differential movements or settlements result in the

redistribution of external reactions and internal forces in the structure. This may in turn result
in the introduction of additional tensile stresses and, therefore, cracking in the concrete
components of the structure. Movement cracks may be of any orientation and width, ranging
from fine cracks above the reinforcement due to formwork settlement, to wide cracks due to
foundation or support settlement.
Figure 2.2.3.2c – Crack/separation in abutment Figure 2.2.3.2d – Shear crack in girder adjacent to
wall due to differential settlement support
2.2.3.3 Significance of cracks
Crack type and widths provide some insight into how the cracks affect structure durability and
strength. The presence of cracks can provide access to moisture and oxygen and the exchange of
aggressive substances beyond cover concrete to embedded steel, promoting corrosion and further
deterioration through cracking, spalling and delamination.
The aggressiveness of exposure conditions will directly influence the likelihood of further deterioration
from cracks. For example, in a marine environment subject to wetting and drying, the presence of
cracks will likely result in severe deterioration over a relatively short period.

The location and orientation of cracks is usually a good indicator of the likely causes.
Another key factor in understanding the significance of cracks is whether they are passive or active.
Passive cracks will be dimensionally stable whereas active cracks continue to grow. This emphasises
the importance of measuring crack widths accurately. Over time, the concrete surface around a crack
deteriorates and spalling of the crack edges will occur. It is important to ensure that the actual crack
width, and not the spalled width is measured (refer Figure 2.2.3.3).
The severity of cracking is reported as a function of the crack width:
Hairline up to 0.1 mm
Minor 0.1 to 0.3 mm
Moderate 0.3 to 0.6 mm
Severe Greater than 0.6 mm.
Figure 2.2.3.3 – Accurate measurement of crack width
2.2.4 Spalling
A spall is a fragment of concrete which has been detached from a larger concrete mass. The causes
of spalling include:
• Corrosion - a continuation of the corrosion process whereby the actions of external loads or
pressure exerted by the corrosion of reinforcement and attendant expansion results in the
breaking off of the delaminated concrete. The spalled area left behind is characterised by
sharp edges.
• Impact - vehicular or other impact forces on exposed concrete edges, deck joints or
construction joints can result in the spalling or breaking off of pieces of concrete locally.
• Compression - overloading of concrete in compression can result in the breaking off of the
concrete cover to the depth of the outer layer of reinforcement. Spalling may also occur in
areas of localised high compressive load concentrations, such as at structure supports, or at
anchorage zones in prestressed concrete.
• External restraint/forces – e.g. restraint forces generated by seized bearings often cause
spalling of the bearing support area on the front face of the bearing shelf.

• Fire – spalling of concrete may result in concrete exposed to extreme temperatures such as
fire.
Examples of concrete spalling are shown in Figure 2.2.4a to Figure 2.2.4d.
Figure 2.2.4a – Spalling of concrete at ends of Figure 2.2.4b – Spalling to front face of headstock
deck units
Figure 2.2.4c – Spalling of slab soffit Figure 2.2.4d – Corner spalling of square pile
2.2.5 Delamination
Delamination is defined as a discontinuity in the surface concrete which is substantially separated but
not completely detached from concrete below or above it. Visibly, it may appear as a solid surface but
can be identified as a hollow sound by tapping. Delamination begins with the corrosion of
reinforcement and subsequent cracking of the concrete. However, in the case of closely spaced bars,
the cracking extends in the plane of the reinforcement parallel to the exterior surface of the concrete
(refer Figure 2.2.6a).

2.2.6 Surface defects
Surface defects are not necessarily serious in themselves however they are indicative of a potential
weakness in concrete. Surface defects include:
• Segregation - the differential concentration of the components of mixed concrete resulting in

non-uniform proportions in the mass. Segregation is caused by concrete falling from a height,
with coarse aggregates settling to the bottom and the fines on top. Another form of
segregation occurs where reinforcing bars prevent the uniform flow of concrete between them.
Segregation is more likely to occur in higher slump concrete.
• Cold joints – these are produced if there is a delay between placement of successive pours of
concrete, and if an incomplete bond develops at the joint due to the partial setting of concrete
in the first pour (refer Figure 2.2.6b).
Figure 2.2.6a – Delamination in culvert slab Figure 2.2.6b – Cold joints in abutment wall
• Deposits – staining/accumulation of material on concrete surfaces where water percolates

through the concrete and dissolves or leaches chemicals from it and deposits them on the
surface. Deposits may appear as:
 efflorescence – a deposit of salts, usually white. Over time can result in stalactites
forming (refer Figure 2.2.6c)
 exudation – a liquid or gel-like discharge through pores or cracks in the surface (refer
Figure 2.2.6d)
 encrustation - a hard crust or coating formed on the concrete surface.

Figure 2.2.6c – Efflorescence evident on concrete Figure 2.2.6d – Discharge through cracks in
headstock concrete surface
• Honeycombing – produced due to the improper or incomplete vibration of the concrete which
results in voids being left in the concrete where the mortar failed to completely fill the spaces
between the coarse aggregate particles (refer Figure 2.2.6e).
• Abrasion - the deterioration of concrete brought about by vehicles scraping against concrete
surfaces, such as decks, kerbs, barrier walls, piers or the result of dynamic and/or frictional
forces generated by vehicular traffic, coupled with abrasive influx of sand, dirt and debris. It
can also result from friction of waterborne particles against partly or completely submerged
members (refer Figure 2.2.6f). This phenomenon is also known as water wash.
• Polishing - a slippery surface may result from the polishing of the concrete deck surface by the
action of repetitive vehicular traffic where inadequate materials and processes have been
used.
Figure 2.2.6e – Concrete honeycombing Figure 2.2.6f – Abrasion of concrete
2.2.7 Scaling
Scaling is the local flaking or loss of the surface portion of concrete or mortar. Scaling is common in
non air-entrained concrete but can also occur in air-entrained concrete in the fully saturated condition.
Scaling occurs in poorly finished or overworked concrete where too many fines and not enough
entrained air is found near the surface. Scaling of concrete is shown in Figure 2.2.7a.

Figure 2.2.7a – Concrete scaling Figure 2.2.7b – Concrete disintegration
2.2.8 Disintegration
Disintegration is the physical deterioration or breaking down of the concrete into small fragments or
particles. The deterioration usually starts in the form of scaling and, if allowed to progress beyond the
level of very severe scaling, is considered as disintegration. Disintegration of concrete is illustrated in
Figure 2.2.7b.
2.2.9 Fire
Concrete structures can sustain damage when exposed to fire depending on the duration and
intensity. The effects of high temperature fires on concrete structures can include:
• reduction in compressive strength
• reduction in modulus of elasticity
• micro-cracking within concrete matrix
• spalling of concrete
• loss of bond between steel and concrete
• possible loss of residual strength of steel reinforcement and/or loss of tension in prestressing
tendons.
2.2.9.1 Effects on concrete
Common changes in concrete properties associated with various peak temperatures are summarised
below:
• Up to 120⁰C – no significant effects.
• Up to 250⁰C – localised cracking and dehydration of cementitious paste, complete loss of free
moisture. Commencement of strength reduction.
• 300 – 600⁰C – significant cracking of cementitious paste and aggregates due to expansion.
Colour of concrete changes to pink.
• 600⁰C – complete dehydration of cementitious paste with associated shrinkage cracking and
honey combing. Concrete becomes friable, very porous and easily broken down. Colour of
concrete changes to grey. Strength lost.

• 1200⁰C – constituent components start to melt.
• 1400⁰C – concrete melts completely.
2.2.9.2 Effects on reinforcing steel
Steel reinforcement can exhibit up to 50% loss in yield strength while at elevated temperatures of
around 600⁰C. Recovery of yield strength will typically occur for temperatures up to 450⁰C for cold
worked steel products and up to 600⁰C for hot rolled steel products. For temperatures beyond these
ranges the loss in yield strength is permanent. The modulus of elasticity is also reduced while the steel
is at elevated temperatures.
Pre-stressing steel is more susceptible to the effects of fire and elevated temperatures because loss of
strength in the order of 50% occurs at temperatures of about 400⁰C. Loss of tension in tendons occurs
due to a combination of the elevated temperature effects and loss of modulus of elasticity of the
concrete.
The bond between steel and concrete can be adversely affected at temperatures greater than 300⁰C
(because of the difference in thermal conductivity and thermal expansion properties between the steel
and cover concrete).
2.3 Steel
The use of steel has progressed from cast iron, wrought iron, rivet steel and plain carbon steel to
notch tough low temperature steel.
The following defects/issues with steel are described:
• corrosion
• protective coating systems
• permanent deformations
• cracking
• loose connections
• impact damage
• fire damage.
2.3.1 Corrosion
Corrosion is the deterioration of steel by chemical or electro-chemical reaction resulting from exposure
to air, moisture, industrial fumes and other chemicals and containments in the environment in which it
is placed. The terms rust and corrosion are used interchangeably in this sense. Corrosion, or rusting,
will only occur if the steel is not protected or if the protective coating wears or breaks down.

Figure 2.3.1a – Mild surface corrosion Figure 2.3.1b – Severe corrosion and loss of
section
All ferrous alloys are susceptible to corrosion deterioration. Unprotected steel, in the presence of
oxygen and moisture and in the absence of contaminants (clean atmospheric conditions) corrodes at
approximately 0.02 mm/year. The rate of deterioration is therefore very slow and it will be many years
before the integrity of a structure is compromised. However, corrosion is accelerated by continuous (or
even intermittent) wet conditions or by exposure to aggressive ions, such as chlorides in de-icing salts
or in a marine environment, and other atmospheric industrial contaminants. In these conditions, steel
becomes vulnerable to both pitting and general corrosion (refer Figure 2.3.1a and Figure 2.3.1b).
Pitting corrosion is a local large reduction in parent metal and can cause a serious reduction in load-
carrying capacity (refer Figure 2.3.1c). It can also lead to local high stresses, which may increase the
risk of fatigue failure.
Other causes of steel corrosion are the flux used in welding (if not neutralised), and direct contact with
dissimilar metals, but, with the exception of bi-metal contact, these are less likely to cause significant
structural deterioration.
Rust on carbon steel is initially fine grained, but as rusting progresses it becomes flaky and
delaminates exposing a pitted surface. The process thus continues with progressive loss of section.
Sulphate Reducing Bacteria (SRB) is a corrosion mechanism of galvanised steel components in

contact with soil water. The reduction of the sulphate content on the steel surface results in a highly
acidic environment within and under the affected area which causes steel corrosion (refer
Figure 2.3.1d). Favourable conditions for SRB growth include oxygen-depleted, marine or freshwater
pervious soils (sediments) containing sulphate at a neutral pH. Further information relating to this
phenomenon can be found in Technical Note 99 Sulphate Reducing Bacteria on Steel Structures.

Figure 2.3.1c – Pitting of steel Figure 2.3.1d – Corrosion of steel by SRB
2.3.2 Protective coating systems
Structural steelwork is normally protected against corrosion by a protective coating system (paint or
galvanising). Weathering steel, which does not require a protective coating, is the only exception.
Corrosion of steelwork is usually associated with the breakdown or inadequacy of the protective
system.
Paint systems suffer from various forms of deterioration such as cracking, flaking, chalking and
peeling. The life of a paint system is normally much less than that of the steel member it is protecting.
Early detection of breakdown is beneficial because it substantially reduces the amount of preparation
that is involved in repair and reapplication. Delays to the maintenance of paint systems can result in
rapidly accelerating increased costs.
Maintenance of steelwork protected by galvanising becomes extremely difficult if remedial action is

delayed until corrosion is well established.
The cause of any white deposit on the surface of paint over zinc metal spray should be investigated as
it may be zinc hydroxide (formed by reaction of zinc with water and air), which is the first sign of the
zinc coating breaking down. If left untreated corrosion of the zinc will become extensive (refer
Figure 2.3.2.a).
Aluminium metal spray is less easily attacked, breakdown usually occurs because the aluminium
spray has been badly applied.
Breakdown of paint over galvanising is often due to the poor adhesion of a wrongly selected paint
system (refer Figure 2.3.2b).

Figure 2.3.2a – White deposit on zinc metal spray Figure 2.3.2b – Failure of paint system over
galvanising
Common types of protective system failure are:
• Blistering - generally caused either by solvents which are trapped within or under the paint
film, or, by water which is drawn through the paint film by the osmotic forces exerted by
hygroscopic or water soluble salts at the paint/substrate interface. The gas or the liquid then
exerts a pressure stronger than the adhesion of the paint (refer Figure 2.3.2c).
Figure 2.3.2c – Blistering of paint system Figure 2.3.2d – Flaking of paint system
• Corrosion blistering - coatings generally fail by disruption of the paint film by expansive
corrosion products at the coating/metal interface. General failure can result from inadequate
paint film thickness. However, local or general deterioration can occur when corrosion is due
to water and aggressive ions being drawn through the film by the osmotic action of soluble
iron corrosion products, as the attack will start from corrosion pits.
• Flaking - flaking or loss of adhesion is generally visible as paint lifting from the underlying
surface in the form of flakes or scales (refer Figure 2.3.2d). If the adhesive strength of the film
is strong then the coating may form large shallow blisters. Causes include:
− Loose, friable or powdery materials on the surface before painting.
− Contamination preventing the paint from ‘wetting’ the surface, i.e. oil, grease, etc.
− Surface too smooth to provide mechanical bonding.
− Application of materials in excess of their pot life.

• Chalking - the formation of a friable, powdery coating on the surface of a paint film caused by
disintegration of the binder due to the effect of weathering, particularly exposure to sunlight
and condensation. This is generally considered the most acceptable form of failure since
maintenance surface preparation consists only of removing loose powdery material and it is
usually unnecessary to blast clean to substrate.
• Cracking - may be visible in increasing extent, ranging from fine cracks in the top-coat to
deeper and broader cracks.
• Pinholes - minute holes formed in a paint film during application and drying. They are caused
by air or gas bubbles (perhaps from a porous substrate such as metal spray coatings or zinc
silicates) which burst, forming small craters in the wet paint film which fail to flow out before
the paint has set.
2.3.2.1 Weathering steel
Weathering steel owes its corrosion protection to the formation of a stable protective oxide film, which
seals the surface against further corrosion. The film is dark brown with a lightly textured ‘rusty’ surface.
Unlike other types of structural steel, weathering steel has a carefully controlled non-ferrous content to
ensure that the oxide film adheres tightly to the substrate. Nevertheless, the surface oxide is slowly
worn away, and replaced by a new film, causing a very slow loss of section over the life of the
structure. The rate of loss depends on the alloy content, air quality and the frequency with which the
surface is wetted by dew and rainfall and dried by the wind and sun. Designs using weathering steels
typically allow for a 1 mm to 2 mm sacrificial loss to sections and fasteners. The location/environment
for the use of weathering steel must be carefully considered in terms of wet climate conditions. Special
attention needs to be paid to management of water run-off and drainage.
2.3.3 Permanent deformations
Permanent deformation or distortion of steel members can take the form of bending, buckling, twisting
or elongation, or any combination of these.
Permanent deformations may be caused by initial distortion, residual stresses, lack of fit, inadequate
design, overloading, impact damage, or inadequate or damaged intermediate lateral supports or
bracing (refer to Figure 2.3.3a and Figure 2.3.3b).
Permanent bending deformation may occur in the direction of the applied loads and are usually
associated with flexural members; however, vehicular impact may produce permanent deformations in
bending in any other member.

Figure 2.3.3a – Buckling of gusset plate Figure 2.3.3b – Impact damage to steel beam
Permanent buckling deformations normally occur in a direction perpendicular to the applied load and
are usually associated with compression members. Buckling may also produce local permanent
deformations of webs and flanges of beams, plate girders and box girders.
Permanent twisting deformations appear as a rotation of the member about its longitudinal axis and
are usually the result of eccentric transverse loads on the member. Permanent axial deformations
occur along the length of the member and are normally associated with applied tension loads.
Any distortion of a member out of plane in the form of waves, kinks or warping can significantly reduce
resistance to compressive load.
2.3.4 Cracking
A crack is a linear fracture of the steel component.
Cracks are potential causes of complete fracture and usually occur at connections and changes in
section. The most common causes are fatigue and poor detailing practices that produce high stress
concentrations. Elements that have been modified since initial construction are also potential problem
areas. Fracture of any member, bolt, rivet or weld is obviously serious and can have important
structural implications.
Fatigue failure is the most common cause of cracking and fracture of steelwork structures. Fatigue is
the process by which a structural member or element eventually fails after repeated applications of
cyclic stress. Failure may occur even though the maximum stress in any one cycle is considerately
less than the fracture stress of the material. Characteristically, a fatigue fractured surface displays two
distinct zones: a smooth portion indicating stages in the growth of the fatigue crack, and a rough
surface, which represents the final ductile tearing or cleaving. Typically, fatigue failures do not exhibit
any significant ductile ‘necking’ and occur without prior warning or plastic deformation (refer
Figure 2.3.4a and Figure 2.3.4b).

Figure 2.3.4a – Fatigue cracking in web Figure 2.3.4b – Cracking in welds
The risk of fatigue-induced failure may exist in bridges:
• not designed for fatigue
• not designed to adequate fatigue criteria
• where materials and manufacturing controls may not have been adequate
• where structural changes may have occurred, which may include the addition of new fixtures
or repair of damage using, for example, welded cleats or brackets, flame cut holes or
strengthening plates
• where operational changes have occurred, such as alterations to carriageway layouts and/or
increased vehicle loading
• where there is evidence of resonance occurring in any of the structural members.
Fatigue starts with fabrication flaws or at locations with high surface stress concentrations such as
weld toes, irregular cut edges and flame cut edges. It then proceeds through the growth of these flaws
until a final failure mode, such as brittle fracture or buckling, occurs. The initial fabrication flaws may
be large or small but in many cases are too small to be detected by eye.
Cracks may also be present in welds because of poor welding techniques or inappropriate materials. If
cracks are detected it is likely that they will be repeated in similar details within the structure.
Cracks may also be caused or aggravated by overloading, vehicular collision or loss of section
resistance due to corrosion. In addition, stress concentrations due to the poor quality of the fabricated
details and the fracture toughness of materials used are contributing factors. Material fracture
toughness will determine the size of the crack that can be tolerated before fracture occurs.
Welded details are more prone to cracking than bolted or riveted details. Grinding off the weld
reinforcement to be smooth or flush with the joined metal surfaces improves fatigue resistance. Once
the cracking occurs in a welded connection, it can extend into other components due to a continuous
path provided at the welded connection, and possibly lead to a brittle fracture.
Bolted or riveted connections may also develop fatigue cracking, but a crack in one component will
generally not pass through into the others. Bolted and riveted connections are also susceptible to
cracking or tearing resulting from prying action, and by a build-up of corrosion forces between parts of
the connection.

Common locations susceptible to cracking are illustrated in Figure 2.3.4c and Figure 2.3.4d. As cracks
may be concealed by rust, dirt or debris, the suspect surfaces should be cleaned prior to inspection.
Cracks that are perpendicular to the direction of stress are very serious, with those parallel to the
direction of stress less so. In either case, cracks in steel should generally be considered serious, as a
parallel crack may for a number of reasons turn into a perpendicular crack. Any crack should be
carefully noted and recorded as to its specific location in the member, and member structure. The
length, width (if possible) and direction of crack should also be recorded.
Figure 2.3.4c – Common crack locations in steel

Figure 2.3.4d – Common crack locations in steel
2.3.5 Loose connections
Loose connections can occur in bolted or riveted connections; and, may be caused by incorrect
installation, corrosion of the connector plates or fasteners, excessive vibration, overstressing, cracking
or the failure of individual fasteners.
Loose connections may sometimes not be detectable by visual inspection. Cracking or excessive
corrosion of the connector plates or fasteners, or permanent deformation of the connection or
members framing into it, may be indications of a loose connection. Tapping the connection with a
hammer is one method of determining if the connection is loose.

2.3.6 Fire damage
Steel progressively weakens with increasing temperature, e.g. the yield strength at room temperature
is reduced by about 50% at 550°C, and to about 10% at 1000°C. There is therefore a risk that steel
members may fail by buckling or deflecting if they are inadvertently heated during a traffic accident
fire. The extent of failure will depend on the loading that the member is carrying, its support conditions,
and the temperature gradient through the cross section.
Secondary effect damage can occur in bearings, movement joints and other structural members if they
are unable to accommodate the large expansions that may occur in a fire. It is unlikely that this will
have been allowed for in design.
In a severe fire unprotected steelwork will lose practically all its load bearing capacity, deform and
distort and will not be suitable for reuse. In a less severe fire, damage may be limited and it may be
possible to retain members after checking for straightness and distortion and the mechanical
properties. Bolted connections often fail through shear or tensile failure or thread stripping. Any
section yielding could have caused severe weakening of connections and it is important that these are
properly inspected.
Fire will also cause blistering and flaking of paintwork.
2.3.7 Impact damage
Impact damage to a steel structure is usually obvious and will vary in significance from abrasion of the
protective coating through to deformation of a component. In severe cases the load carrying capacity
of a component may be compromised.
2.4 Timber
Timber was extensively used for bridges constructed up until the middle 1900's and these constitute
10% of the structures on the State Declared Road network. The largest proportion of timber bridges
occurs on roads of lesser importance such as local roads, but many timber bridges are still in service
on higher class roads and are often required to carry heavy traffic loadings.
The major causes of deterioration in timber bridges are as follows:
i. fungi (rotting)
ii. termites
iii. marine organisms
iv. corrosion of fasteners
v. shrinkage and splitting
vi. fire damage
vii. weathering
viii. flood damage.
2.4.1 Fungi
Severe internal decay of timbers used for bridges is caused mainly by ‘white rot’ or ‘brown rot fungi.
External surface decay, especially in ground contact areas, is caused by ‘soft rot’ fungi. Other fungi
such as mould and sapstain fungi may produce superficial discolorations on timbers but are not
generally of structural significance.

Fungal growths will not develop unless there is a source of infection from which the plants can grow.
Fungi procreate by producing vast numbers of microscopic spores which may float through the air for
long periods and can be blown for considerable distances.
Although it is true to say that no timber components in service will be free from decay because of an
absence of infecting spores, these spores will not germinate and develop unless there is:
• an adequate supply of food (wood cells).
• an adequate supply of air or oxygen (prolonged immersion in water saturates timber and
inhibits fungal growth)
• a suitable range of temperatures (optimum temperatures are 20⁰C – 25⁰C for soft rots, while
their rate of growth declines above or below the optimum with a greater tolerance of lower
temperatures apparent)
• a continuing supply of moisture (wood with a moisture content below 20% is considered safe
from decay, while many fungi require a moisture content above 30%).
Figure 2.4.1a – Fungal fruiting body and decay of Figure 2.4.1b – Decay pocket in girder
girder
Once established, the decay fungi continue to grow at an accelerating rate as long as favourable
conditions prevail. Depriving the fungi of any one of these required conditions will effectively curtail the
spread of decay. Wood that is kept dry or saturated will not rot. Moisture change can affect decay
indirectly because drying often leads to surface checks, which may expose untreated parts of timber
or create water trapping pockets. Proper preservative treatment effectively provides a toxic barrier to
the fungi's food supply, thus preventing decay.
Figure 2.4.1a and Figure 2.4.1b show rotting of members. The most common rotting areas in timber
bridges are internally in log girders, corbels, headstocks and piles (piping), and in sawn decking at the
exposed ends and interface with kerbs. Decay is often more pronounced at the ends of members.
2.4.2 Termites
Australia has a large number of different species of termites (300) which are widely distributed.
Practically all termite damage to timber bridges occurs through subterranean termites (especially
Coptotermes acinaciformis and allied species) which require contact with the soil or some other

constant source of moisture. Some dry wood termite species are found in coastal areas of
Queensland, but minimal damage is attributable to these types in bridges.
Termites live in colonies or nests which may be located below ground in the soil, or above ground in a
tree stump, hollowed out bridge member or an earth mound. Each colony contains a queen, workers,
soldiers and reproductives or alates. The workers, who usually constitute the highest portion of the
population, are white bodied, blind insects some 3 mm in length which have well developed jaws for
eating timber. However, in North Queensland, termites growing to 20 mm or more in length
(Mastotermes darwiniensis) are found and these are capable of causing significant damage in a short
time compared to the most commonly distributed species.
Attack by subterranean termites originates from the nest, but may spread well above ground level,
either inside the wood or via mud walled tubes called galleries which are constructed on the outside of
bridge members (refer Figure 2.4.2a and Figure 2.4.2b). These galleries are essential for termites as
they require an absence of light, a humid atmosphere and a source of moisture to survive. At least
once a year the alates develop eyes and wings and leave the nest under favourable weather
conditions to migrate up to 200 m from the original nest. After migration, their wings fall off and a few
of these may pair to start new colonies.
Figure 2.4.2a – Termite nest on bridge Figure 2.4.2b – Termite gallery on pier headstock
pile
Termite attack, once established, usually degrades timber much more quickly than fungi, but termite
attacks in durable hardwoods normally used in bridge construction is usually associated with some
pre-existing fungal decay. This decay accelerates as the termites extend their galleries through the
structure, moving fungal spores and moisture about with their bodies. Hence, although some of the

material removed by termites has already lost structural strength because of decay, the control of
termites remains an extremely important consideration.
Basically, there are two main strategies in termite control:
• eradication of the nest (by either direct chemical treatment or by separation of the colony from
its sustaining moisture)
• installation of chemical and physical barriers to prevent termites from entering a bridge or
attacking timber in contact with the ground.
In practice it may be difficult to eradicate the nest because of the problem of locating it.
2.4.3 Marine organisms
Damage to underwater timber in the sea or tidal inlets is usually caused by marine borers, and is more
severe in tropical and sub-tropical waters than in colder waters.
The two main groups of animal involved are:
• Molluscs (teredinindae) - this group includes various species of Teredo, Nausitora and bankia.
They are commonly known in Australia as teredo or "shipworm". They start life as minute,
free-swimming organisms and after lodging on timber they quickly develop into a new form
and commence tunnelling. A pair of boring shells on the head grow rapidly in size as the
boring progresses, while the tail with its two water circulating syphons remains at the original
entrance. The teredine borers destroy timber at all levels from the mudline to high water level,
but the greatest intensity of the attack seems to occur in the zone between 300 mm above and
600 mm below tide level. A serious feature of their attack is that while the interior of the pile
may be eaten away, only a few small holes may be visible on the surface (refer Figure 2.4.3a).
• Crustaceans - this group includes species of Sphaeroma (pill bugs), Limnoria (gribbles), and
Chelura. They attack the wood on its surface, making many narrower and shorter tunnels than
those made by the teredines. The timber so affected is steadily eroded from the outside by
wave action and the piles assume a wasted appearance or "hourglass effect" (refer
Figure 2.4.3b). Attack by Sphaemora is limited to the zone between tidal limits, with the
greatest damage close to half-tide level. They cannot survive in water containing less than
1.0 - 1.5 percent salinity, but can grow at lower temperatures than the teredines.

Figure 2.4.3a – External damage to timber Figure 2.4.3b – Timber piles subject to
pile from shipworm Sphaemora attack
Many strategies have been developed for the control of marine borers but, assuming that the piles
have sufficient remaining strength, the most effective work by reducing the oxygen content of water
around the borers.
2.4.4 Corrosion of fasteners
Corrosion of steel fasteners can cause serious strength reductions for two related reasons. Firstly, the
steel fastener reduces in size and weakens, and secondly a chemical reaction involving iron salts from
the rusting process can significantly reduce the strength of the surrounding wood (this is not fungal
decay but may enhance corrosion of the fastener because of water ingress in the softened timber).
Galvanised fasteners in contact with timber which has been freshly treated with CCA preservative may
exhibit enhanced corrosion. However, for CCA treated timber that has been cured for six weeks,
normal corrosion rates for fasteners will apply.
2.4.4.1 Shrinkage and splitting
Moisture can exist in wood as water or water vapour in the cell cavities and as chemically bound water
within the cell walls. As green timber loses moisture to the surrounding atmosphere, a point is reached
when the cell cavities no longer contain moisture, but the cell walls are still completely saturated with
chemically bound water. This point is called the ‘fibre saturation point’. Wood is dimensionally stable
while its moisture content remains above the fibre saturation point, which is typically around 30% for
most timbers. Bridges are normally constructed from green timber which gradually dries below its fibre
saturation point until it reaches equilibrium with the surrounding atmosphere. As it does so, the wood
shrinks but because it is anisotropic, it does not shrink equally in all directions. Maximum shrinkage
occurs parallel to the annular rings, about half as much occurs perpendicular to the annular rings and
a small amount along the grain.

Figure 2.4.4.1a – Splitting in timber pile Figure 2.4.4.1b – Splitting in timber headstock
The relatively large cross section timbers used in bridges lose their moisture through their exterior
surfaces so that the interior of the member remains above the fibre saturation point while the outer
layers fall below and attempt to shrink. This sets up tensile stresses perpendicular to the grain and
when these exceed the tensile strength of the wood, a check or split develops, which deepens as the
moisture content continues to drop. As timber dries more rapidly through the ends of the member than
through the sides, more serious splitting occurs at the ends. Deep checks provide a convenient site for
the start of fungal decay. Figure 2.4.4.1a and Figure 2.4.4.1b show longitudinal splitting of timber
headstocks and piles.
Shrinkage also causes splitting where the timber is restrained by a bolted steel plate or other type of
fastening. This splitting can be avoided by allowing the timber to shrink freely by using slotted holes.
As timber shrinks, it tends to lose contact with steel washers or plates, so the connection is no longer
tight. Checking the tightness of nuts in bolted connections is therefore a standard item of routine
maintenance for timber bridges.
2.4.5 Fire
Wood itself does not burn. The effect of heat is firstly to decompose the wood (a process known as
'pyrolysis') and it is some of the products of this decomposition that burn if conditions are suitable. This
concept is important in discussions on the action of retardants.
In theory, wood decomposes even at temperatures as low as 20⁰C (at the rate of 1% per century). At
93⁰C the wood will become charred in about five years.

When wood is heated, several zones of pyrolysis occur which are well delineated due to the excellent
insulating properties of wood (thermal conductivity roughly 1/300 that of steel). These zones can be
described generally as follows:
• Zone A: 95⁰C – 200⁰C.
• Water vapour is given off and wood eventually becomes charred.
• Zone B: 200⁰C – 280⁰C.
• Water vapour, formic and acetic acids and glyoxal are given off, ignition is possible but
difficult.
• Zone C: 280⁰C – 500⁰C.
Combustible gases (carbon monoxide, methane, formaldehyde, formic and acetic acids, methanol,
hydrogen) diluted with carbon dioxide and water vapour are given off. Residue is black fibrous char.
Normally vigorous flaming occurs. If, however, the temperature is held below 500⁰C, a thick layer of
char builds up and because the thermal conductivity of char is only 1/4 that of wood, it retards the
penetration of heat and thus reduces the flaming.
• Zone D: 500⁰C – 1000⁰C
In this zone the char develops the crystalline structure of graphite, glowing occurs and the char is
gradually consumed.
• Zone E: above 1000⁰C
At these temperatures the char is consumed as fast as it is formed.
As the temperature of the wood is lowered, the above mentioned behaviour still holds, e.g.,
combustion normally ceases below 280⁰C.
Large section round timbers, as used in bridge construction, have good resistance to fire, and, except
during a severe bush fire, usually survive quite successfully.
2.4.6 Weathering
Weathering is the gradual deterioration of sawn or log timber due to its exposure to sun, wind and rain.
Weathering can be a serious problem especially to the exposed end grain of untreated or unprotected
wood, where severe rotting can occur around the connections. The exposed ends of transverse deck
planks are susceptible to this defect.
2.4.7 Floods
Floods can have a disastrous affect particularly on timber structures. This is due to:
• extra pressure from the flood waters and debris
• log impact on the substructure. If the flood is high enough, the super-structure can also be
damaged by the flood waters.
2.5 Masonry
Masonry construction comprises individual stones, bricks or blocks bonded together by mortar.
Although not a common construction material today, masonry has been used in retaining walls,
abutments, piers and arches. Types of masonry construction are Ashlar masonry, squared stone
masonry and rubble masonry.

The following defects commonly occurring in masonry are described:
i. cracking
ii. splitting, spalling and disintegration
iii. loss of mortar and stones.
2.5.1 Cracking
A crack is an incomplete separation into one or more parts with or without space in between. Cracks
develop in masonry as a result on non-uniform settlement of the structure, thermal restraint and
overloads.
Cracks develop either at the interface between the stone and mortar, following a zigzag pattern, when
the bond between them is weak; or, go through the joint and stone in a straight line, when the mortar
is stronger than the stone.
2.5.2 Splitting, spalling and disintegration
Splitting is the opening of seams or cracks in the stone leading to the breaking of the stone into large
fragments.
Spalling is the breaking or chipping away of pieces of the stone from a larger stone.
Disintegration is the gradual breakdown of the stone into small fragments, pieces or particles.
The splitting, spalling and disintegration of masonry is caused by the actions of weathering and
abrasion; or, by the actions of acids, sulphates or chlorides, which cause deterioration in certain types
of stones, such as limestone.
2.5.3 Loss of mortar and stones
Loss of mortar is the result of the destructive actions of water wash, plant growth or softening by water
containing dissolved sulphates or chlorides. Once the mortar has disintegrated it may lead to loss of
stones. Excessive loss of mortar will also reduce the load-carrying capacity of a structure.
2.5.4 Arch stones dropping
Adopted from VicRoads Road Structures Inspection Manual (Ref. 12):
Ground or foundation movement or severe vibration can cause stone blocks to displace and
drop relative to other stones in an arch. This can also be exacerbated if the quality of the
stones or mortar is poor and failing.
2.5.5 Deformation
Adopted from VicRoads Road Structures Inspection Manual (Ref. 12):
Arches are either semi-circular, segmental (i.e. part of a semi-circle) or elliptical in shape. The
regular curvature may become deformed if the arch is overloaded or if there is differential
settlement of the foundations. Deformation may be accompanied by cracking and dropped
stones. The position and degree of deformation should be recorded.

2.6 Fibre Reinforced Polymers (FRP)
2.6.1 FRP strengthening
Fibre Reinforced Polymer (FRP) composites are used to strengthen reinforced and prestressed
concrete members which are deficient in moment, shear or bursting capacity. The fibres can be
Carbon, Aramid or Glass. The FRP material can be used in the form of flexible sheets to wrap around
the member or in the form of plates. Plates comprise one of the three fibre types, typically in a resin or
epoxy matrix. The system relies on the high tensile capacity of FRP and the bond between the FRP
and the steel or concrete beam.
FRP strengthening can be detrimentally affected by overloading of the structures, extreme

temperature, moisture absorption and high UV exposure. The effects are exacerbated by defects
introduced in the materials during manufacture, handling and installation. The strengthening method
relies entirely on the anchorage and bond of the FRP material to the base component.
The following areas should be inspected and recorded:
• The ends of the strengthened area for signs of the FRP strips debonding from the epoxy resin
or the resin debonding from the concrete base.
• The visible concrete surface at the edge of the strengthening for signs of cracking or spalling
which could affect bonding between the FRP and the member.
• The whole of FRP surface for signs of delamination from the concrete or any irregularities in
the material such as blistering or folding.
• Tears, cuts or crazing of the FRP material.
If any area is classified as being in condition states 3 or 4, pull-off testing should be conducted in the
surrounding FRP to ensure the full extent of the problem is identified. Repair should not be instigated
until the whole area of the defect has been identified.
2.6.2 FRP components
In addition to strengthening of existing components, FRP girders are increasingly being used to
replace hardwood timber components at end of life and have also been trialled for construction of new
superstructures.
Two systems currently in use on the network for component replacement are the Wagners fibre
composite girder (Wagners FC) and the Loc Composites developed fibre composite hybrid girder.
The Wagners FC girder comprises FRP pultrusions, steel reinforcement and exterior flow coat (refer
Figure 2.6.2a and Figure 2.6.2c).
Loc Composites’ fibre composite girder comprises chemically treated plantation softwood Laminated
Veneer Lumber (LVL) with several glass pultrusions/steel modules incorporated into the section (refer
Figure 2.6.2b and Figure 2.6.2d).

Figure 2.6.2a – Wagners FC girder (1st Figure 2.6.2b – Loc Composite Hybrid girder (1st
generation) generation)
Figure 2.6.2c – Wagners FC girder (2nd Figure 2.6.2d – Loc Composite Hybrid girder (2nd
generation – WCFT S1, S2 & S3) generation -LOC 400 & LOC 420))
Areas of concern relating to durability/deterioration of FRP components align with the constituent
materials. For example:
• delamination/debonding of FRP elements
• decay/insect attack of timber/LVL elements
• corrosion of steel components
• corrosion/tightness of fixings.
In addition, cracking of components, distortion/displacement, crushing, excessive deflection along with

impact and fire damage are all indicators of deterioration/distress.

3 Common defects observed in existing structures

3.1 Concrete bridges
The following section lists the various types of reinforced and prestressed concrete bridges and
generally lists the main problems associated with each type.
3.1.1 Monolithic and simply-supported T-beams
Most monolithic structures are T-beam bridges with the whole structure cast insitu. Spans tend to be
small but groups of as many as five continuous spans may be built this way in a bridge. This puts
strains on the columns of the piers and at the abutments due to temperature movements, and it is not
uncommon to see a crack and signs of movement around the beam/wall joint at the abutment. There
may also be signs of tension cracking in the face of the columns of the furthest pier from the centre of
the span group, due to movements and temperature. These structures are often overstressed in
negative moment with cracking and staining observed at the underside of deck at the beam/deck/pier
diaphragm joints.
The T-beam bridges often have sufficient shear reinforcement near the supports and diagonal shear
cracking may be observed as far away as one third of the span from the support. The abutments and
wings were usually cast as one and heavy cracking, spalling and movements may be observed at the
wing joint especially where high abutment walls were built.
The simply-supported precast T-beam structures tended to be a later design with improved shear
reinforcement of the beams and hence shear cracking is not normally seen. Some flexural cracking of
the beams will normally be seen at midspan especially on structures which carry a reasonable number
of heavy loads. Some beams had a locating dowel at one end of span which made that end of beam
fixed with the other end free to move. The allowance for movement was often lost, with the
consequence that the beam moved relative to the dowel, cracking and sometimes spalling the ends of
the beams. The support directly under the beams also tended to spall due to friction, as a layer of
malthoid was all that often separated the beam and substructure.
3.1.2 Precast ‘I’ beams
Precast ‘I’ beam construction began in the early 1960's, using precast high strength prestressed
concrete beams with spans up to 22 metres approximately. These beams have generally performed
well over the years.
The National Association of Australian State Road Authorities (NAASRA) beam sections came into
use in 1970 and Type 3 and Type 4 girders have been used extensively for spans up to
25 m and 31 m respectively. Longer spans have been accomplished by casting load bearing
diaphragms at the piers which encased the ends of the beams to create continuous spans. The beams
were also connected on the bottom flange by heavy steel bars welded together. In recent years a ‘bulb
tee’ section has been used in place of the Type 4 NAASRA beam for spans up to 36.5 metres.
The biggest problem associated with prestressed beams for large spans is the amount of hog of the
beam, especially as they continue to hog further after delivery until loaded by the weight of the bridge
deck. The beams can also crack towards the ends due to stressing if insufficient end steel in provided.
3.1.3 Precast prestressed inverted ‘T’ beams
These beams were used during the 1970's to produce a flat soffits to bridges crossing the highways.
This was done for aesthetic reasons as the flat soffit is more appealing to the driver than the

interrupted underside of an ‘I’ beam bridge. Spans were usually in the region of 10 metres. These
beams were not an efficient section and lost favour with designers. No problems have been
encountered with these types of structures to date. Top slab construction or concrete infill between
beams have both been used.
3.1.4 Box girder bridges
Box girder bridges have been used extensively on or over freeways in Queensland. They are
generally cast-in-place and then post-tensioned. Some box girders have been precast in segments
and post tensioned when erected in place. Problems can regularly occur during construction and at
post-tensioning.
The major maintenance concern for these bridges is where grouting around the post tensioning is
incomplete and does not adequately protect the steel tendons. Serious concerns have been identified
in some overseas countries where de-icing salts are used on the deck but to date no evidence of
tendon corrosion has been observed in Queensland bridges.
3.1.5 Prestressed voided flat slab bridges
A number of cast-in-place prestressed voided flat slab bridges have been built on or over freeways
and highways and these provide an attractive shallow depth superstructure, ideal for very wide bridges
and with spans to approximately 34 metres. Problems with flotation and distortion of the void formers
have been experienced during construction, but these structures are relatively cheap, aesthetically
pleasing, and have performed well up to now.
3.1.6 Reinforced concrete flat slabs
These structures are monolithic cast-in-place and have performed very well with the slab providing
considerable lateral load distribution. Structures can be continuous over a number of spans, hence
there is a possibility of cracking of the columns due to movement.
The slabs themselves often have a shrinkage crack which runs almost directly down the centreline of
the slab. Provided this remains dry it is of no concern.
3.1.7 Precast prestressed deck units
Introduced in 1954 these units are held together by transverse tensioning rods in cored holes.
This has been the principal form of bridge superstructure constructed over the last thirty years. These
596 mm wide, rectangular section, voided planks cover the span range from 8.0 to 27.0 m varying in
depth from 300 to 900 mm respectively.
Typically these elements are erected with a 20 mm gap between adjacent units which is subsequently
filled with poured mortar. The mortar acts both as a shear key and a means of providing an even
bearing surface between units for the transverse prestressing forces. The latter is applied by way of
transverse stressing bars slotted through cored holes in the units. Following the application of
prestress force the gaps around the bars and joints at the ends of units, at piers and abutments, are
also filled with mortar.
The mortar in the joints inevitably cracks as a consequence of shrinkage and girder deflections and
rotations. This permits water to penetrate from the surface to the unit soffits and substructure
elements. Recently there have been failures of the transverse stressing bars which have corroded as
a consequence of this. Additionally, in regions where Alkali-Silica Reaction (ASR) is a problem that
reaction is exacerbated by water leaking through the deck. The extent and severity of cracking and the

production of reaction products are more pronounced in the wetter areas of the bridge. That is,
adjacent to the joints between units and spans and around the kerb unit. It is imperative that deck
drainage is efficient on those structures and that any cracking of the surfacing around deck joints is
sealed. Current designs detail waterproofing of the longitudinal joints between units to avoid the
problems discussed above.
The anchor plate and ends of transverse stressing bars are usually exposed. In an aggressive
environment, these components may be heavily corroded. In addition, the threaded ends of the
transverse stressing bars may not have sufficient length. In some instances these components are
installed in the formed voids on the external concrete plank which are filled with mortar to protect them
from corrosion.
Generally, the deck units alone comprise the superstructure however a reinforced concrete deck slab
acting compositely with the units is often adopted in lieu of the transverse prestressing. Currently the
slab is made continuous at fixed pier joints to improve ride and minimise the number of pier joints.
Erection of deck units on elastomeric bearings, especially at expansion joints, can be compromised by
excessively hogged units or lateral shearing on headstocks with crossfall unless the unit is supported
and braced adequately until the levelling layer of epoxy has cured.
3.1.8 Precast prestressed voided ‘T’ beams
These standard beams were originally developed in 1986 by VicRoads and subsequently introduced
in Queensland. With initial spans from 8 to 19 m, the original design has evolved to include Super-T
and T-roff beams with span ranges up to 35 m and beam depths up to 1.8 m.
The potential problems identified with these beams include high neoprene bearings placed on sloping
headstocks beneath the T-beams and loss of cover due to void formers floating during fabrication.
3.1.9 Decks and overlays
Reinforced concrete decks are usually cast-in-place over beams. For high structures or bridges over
highways and railway lines, thin precast prestressed concrete formwork slabs or sacrificial formwork is
usually used to negate the need for stripping after casting the deck.
The concrete beams have ligature bars which project into the deck for composite action, whilst steel
beams and girders have welded stud or other anchors at their top to provide composite action. On
some older bridges a bevelled concrete cap was cast between the deck and beams. Cracking of the
cap can occur along the fillet line at the deck, or cracking coinciding with the location of the shear
connectors may be visible. Unless severe, this cracking is not cause for concern.
A 50 mm or larger thickness of bituminous wearing surface is generally laid over concrete decks
however earlier concrete decks were increased in depth by 12 mm to provide an unsealed wearing
surface. This practice has now been discontinued due to temperature cracking of the surface which
allowed moisture to penetrate into the deck concrete.
3.1.10 Diaphragms
At the ends of the deck a stiffening beam will be noticed joining the ends of the beams. This
diaphragm (cross-girder) may be the full depth of the beams, but on some structures it will only be in
the order of 200 to 250 mm in depth.
Diaphragms may also be found at midspan or at the third points to provide web stiffening against
debris loads and impact forces and aid in load distribution between beams.

On precast prestressed 'I' beam bridges continuous for live load, a wide heavily reinforced load
bearing diaphragm can be found at the piers. This diaphragm is required to support the full
superstructure loads and transfer that load back to a pier or to isolated columns which form the pier.
All these diaphragms should be checked for cracking.
3.1.11 Kerbs, footways, posts and railing
Most early concrete bridges used either narrow kerbs (sometimes tapered in cross section) or wider
kerbs tapered (in plan) at the ends. These kerbs had a barrier facing which was stepped back from the
kerb face. This caused a dangerous situation whereby errant vehicles could ‘take-off’ and land on top
of the barrier rather than be redirected by it.
Where footways are constructed on bridges they should be inspected for pedestrian safety, i.e. ensure
level of precast or cast-in-place footway slabs is good with no depressions or rises which could trip
pedestrians. Moisture will penetrate the footway slabs and adequate drainage of the area under the
footway is required. If drainage is not adequate weed growth will form and the underside of deck will
form efflorescence with the dampness penetrating the deck.
Many different forms of post and railing have been used on concrete bridges ranging from guideposts,
timber posts and rails, reinforced concrete posts with precast reinforced concrete rails, reinforced
concrete posts with steel tube rails, steel channel posts with steel guardrail, rectangular rolled hollow
steel posts and rails, and reinforced concrete new jersey barriers with steel posts and rail on top.
Pedestrian grating is usually associated with footways, or on pedestrian bridges, and should be
inspected for damage and tightness of the attachment bolts.
For all bridges it is important for the steel guardrail on the approaches to attach to the bridge endposts
or to continue over the bridge. This will prevent the possibility of a vehicle hitting the approach rail and
being redirected directly into the endposts or striking an unprotected endpost.
3.1.12 Abutments
Abutment types vary but will generally be one of the following types:
• spill through abutments using a reinforced concrete headstock supported on driven precast
concrete piles or of a frame type with reinforced concrete columns supported by a footing
below ground
• wall type abutments either reinforced or mass concrete
• wall type consisting of straight columns and a headstock with infill wall panels between the
columns
• masonry walls
• spread footing
• sill beams behind a reinforced earth wall.
Spill through abutments are possibly the most common type to be found and usually have little or no
cracking of the headstock, except for shrinkage cracks. Frame type headstocks are more highly
stressed and some flexural cracking may be found at midspan between the columns, or over the
columns. Loss of retaining fill in front, beneath and behind the headstocks is also a common problem
which requires correcting to retain the embankment fill behind the abutment.

The columns or piles are not usually a problem although cracking of the front face of piles has been
noticed where the superstructure has propped the abutment against large movements of the
embankment fill. This is only a problem if the cracking becomes severe. The ballast walls will often
crack if beams bear hard against them or if an overhanging deck puts pressure of the top of the wall.
This cracking is not considered very important provided excess moisture is not allowed through the
walls.
Wall abutments are usually in good condition with differential movement between panels the only area
of concern. Mass concrete walls are usually small in height and have only movement problems or in
some instances scour problems of fill in front of, and beneath, the footing. Wall abutments consisting
of columns with headstocks and thin infill panels can have cracking from the effects of earth pressure
and shrinkage.
The side wings on the high abutment walls often move relative to the abutment walls due to earth
pressure. The wings are not normally self-supporting and rely on a concrete key or few bars of light
reinforcement to hold them in place. Cracking and differential movement between the wing and the
abutment wall are quite common and can be a problem if severe.
Highway and freeway structures are designed to have reinforced concrete approach slabs which rest
on top of the ballast walls. These are installed to eliminate live load earth pressures behind the
abutments and to provide a smooth transition onto and off the bridge for fast moving and heavy traffic,
thus reducing the impact loads on the structure.
Stone masonry abutment walls have been constructed on older structures. Care should be taken in
assessing these walls for possible signs of settlement of the blocks, settlement cracking or cracking of
the wall especially under heavily loaded areas. Where loadings on the wall are at isolated points such
as girders rather than a distributed load, a reinforced concrete cap may be cast on top of the wall to
distribute the stress.
If this cap overhangs the masonry for a bridge widening, particular attention should be noted of the
edge loading occurring on the masonry.
3.1.13 Piers
Piers of various types include headstocks supported on piles or columns, wall type piers some of
which consist of columns with a headstock and thin in full panels, straight walls of constant or variable
thickness, box type concrete piers and masonry piers.
Cracking of these pier types will be similar to the cracking mentioned above for the abutments. With
the higher wall piers horizontal cracking may occur around the construction joints.
With continuous superstructures and large movements occurring at the abutments, horizontal cracking
of the pier wall or column face can occur as bending pressure is exerted on the wall.
Bending pressure can also be put on high slender columns or piles if the bridge is on a large skew or a
sharp circular curve, causing lateral cracking of the piers low down.
Long monolithic T-beam bridges often have split piers at the deck expansion joints. Cracking and
spalling is a problem with these piers due to the high moments on the slender sections.
Portal frame and cantilevered headstocks have, in some instances, been found to have theoretically
insufficient bending or shear capacity. This could lead to the development of structural cracking in the
headstock.

Many of the older structures have poor quality sandy concrete which can suffer severely from the
action of water, sand, pebbles and grit as they wash past. This can significantly reduce the amount of
cover concrete to the steel reinforcement and guniting may have been used to reinstate the concrete
surface.
3.2 Steel bridges
Composite steel beams with reinforced concrete decks were used in the past for longer span
structures but are seldom used today. The reasons for this were cost, (fabricated plate girders are
much more expensive than prestressed concrete beams) and future maintenance problems with
repainting.
These superstructures also tend to deflect substantially and continuous steel girders vibrate with
loading of adjacent spans. Because of this movement under load, the reinforced concrete deck will
often crack through at approximately the third points of the spans. Moisture, corrosion and
efflorescence at the cracks will normally be seen on these type of structures.
Steel beams should be checked for signs of corrosion and the condition of the paintwork noted. Simply
supported beams should have steel angle cross-frames or concrete diaphragms at midspan to prevent
lateral buckling and aid in stiffening the beams. Continuous beams should have these at the supports
and at midspan. Splice plates on the web, top and bottom flanges should be inspected to ensure no
weld cracking or separation has occurred. All welded connections, splices and stiffeners should be
closely inspected for any signs of cracking of the weld or metal immediately adjacent to it.
Bolted and riveted connections require inspection to check whether all connections are tight, intact
and the protective cover is in good order. Loose bolting can sometimes be detected by cracks in the
coating system, movement of the bracing or by associated noises as transient loads cross the deck.
Any signs of excessive wear at pinned joints in trusses or other movement joints should be observed
and recorded.
Areas around the junction of members should be inspected for straightness as these can be the first
sign of permanent deformation resulting from buckling of compression flange or member or a sign of
inadequate bracing.
The thin steel sections are also susceptible to permanent deformation caused by vehicle impact and if
severe can significantly reduce the load carrying capacity of the structure. This can be caused by
impact from a high vehicle travelling under bridge damaging the bottom flange or chord member, or by
vehicles at deck level causing damage to through girders and trusses.
3.3 Timber bridges
The following section is a general description of common defects found in timber bridges. For a
detailed description of element-specific defects, refer to Parts One and Two of the Timber Bridge
Maintenance Manual.
3.3.1 Timber girders
Timber girders may be either round, hewn or sawn. Hewn or sawn girders will generally not have any
outer sapwood except in the case where CCA preservative treatment has been applied.
Timber girders should be inspected for pipe or external rot at their maximum stress location at
midspan. Inspection at the girder ends should also be carried out as pipe rotting is generally more

severe at these locations. Girder ends are prone to crushing failure when excessive loss of section
has occurred.
The girders should also be checked at their ends for splitting (some timber girders may have anti-split
bolts at their ends to control any splitting), they should have full bearing on corbels and they should be
checked for end rot especially at abutments where moisture or wet fill is prevalent.
Splitting of timber girders can affect their performance and working life considerably. Much of the
splitting will be along the grain and, unless severe, is not of significance unless it allows considerable
moisture into the splits. Spiking of the decking to the timber girders can cause splitting at the top, and,
with the presence of moisture and vibration of the spikes under traffic, spike rot of the girders occurs.
For this reason spiking of decking directly to girders should be avoided. Generally, decking will be
spiked to a sacrificial spiking plank on the outer girders with no spike connection to inner girders.
Longitudinal cracking of girder ends, when combined with large pipe size, will lead to the girder section
being split into a number of discrete segments which will reduce shear and crushing strength at the
support ends.
If the girder is severely split in the vertical plane loading can tend to widen the splits causing
premature failure. By far the most dangerous splits are the fracture of the timber due to overloading,
and the split which starts from the bearing area and travels diagonally across the timber grains
towards the top of the girder. In both cases the girders will require relieving or replacing, though steel
banding could control the diagonal splitting if load limits are placed on the structure.
Other problems which may occur with timber girders are the presence of rotting knot holes (especially
if at midspan), sagging of the girder at midspan, or excessive deflection of the girder under live load
due to poor lateral distribution of the decking, or the member being too small for the span.
Loss of section due to termite attack can seriously affect the performance of timber girders and care
should be taken in searching for any evidence of their presence.
3.3.2 Corbels
Corbels should be checked for splitting and pipe rot at their ends. If piping or splitting is severe then
crushing of the corbel can occur with subsequent excessive vertical movement of the timber girder at
the end. Many corbels have anti-splitting bolts through their ends in an attempt to prevent crushing
from occurring.
3.3.3 Decking (timber and steel trough)
3.3.3.1 Transverse planks
The most common form of decking consists of transverse planks spiked to the outer girder spiking
plank with no mechanical connection to the internal girders. The ends are also restrained by the
bolting down of the kerbs and jacking of internal girders (cambering) is used to provide tightness to the
whole superstructure. However, this type of structure will always work loose due to shrinkage and
creep in the members and will require continual tightening of bolts and recambering. Timber running
planks are often used with transverse deck planks and these planks aid in load distribution to the deck
planks. The running planks are usually of a thin section (about 50 mm thick) and being usually spiked
down, tend to work loose quite easily. They tend to split quite easily, requiring constant replacement
and form a moisture trap which hastens rot of the decking beneath. Longitudinal timber distributor
planks are often bolted to the bottom of the decking to reduce differential movement between the
transverse deck planks under the action of wheel loads. Though distributors may help with load

support in deteriorated decking, they are of no benefit in improving the distributing of loads to the
girders. Most bridges have an asphalt or penetration macadam wearing surface over the transverse
decking, but the surface becomes quite bumpy and cracked due to movement of the decking below,
although it does offer improved load distribution. It also tends to build up a reservoir of moisture which
rots out the timber at a quicker rate.
Transverse deck planks should be inspected for end and top rot (particularly in the kerb region)
bulging on top due to ingress of water, sagging at midspan due to excessive span length, fracture and
severe splitting. Severe splitting and top rot can often be caused by spiking of decking and the
practice should be discouraged except at the outer edge connection.
The inspector must always be alert for signs of termite damage as the consequence on these small
sections can be severe.
3.3.3.2 Plywood decking
CCA treated plywood is often used for deck replacement on timber bridges.
Differential movement of sheets under traffic loads and inadequate sealing of joints can cause
damage to the roadway surface. As well, the long term performance of the ply in wet tropical areas, or
where submergence is common should be monitored to check for delamination of the plys. The
exposed outer ends of the sheets should also be examined for evidence of delamination.
Common defects of plywood decking and the root causes include the following:
• Loss of cross sectional area in the bottom layer of due to abrasion between the girder and
plywood panel.
• Abrasion between sheet joints caused by material from the deteriorated deck wearing surface
working their way between the sheets.
• Deck wearing surface had been lost over significant areas resulting in the top scarf jointed
layer being worn away due to traffic abrasion in places (refer Figure 3.3.3.2a).
• Deck bolt washers are less than the specified size causing localised crushing of wood fibre
around the bolts. This has contributed to loose panels which are able to ‘grind’ and flog on the
girders.
• Broken pieces of deck wearing surface work their way down between the sheets contributing
to the grinding action of plywood sheets on the girder seating.
• Plywood panels are loose, evidenced by the pronounced transverse cracking in the deck
wearing surface over every panel joint and by the total loss of the bottom outer layer of the
plywood - girder interface.
• The underside of the bridge has been subjected to severe fire damage resulting in the loss of
the bottom layer and spongy material above the fire damaged section. The latter could be
indicative of changes to the wood structure due to the heat of the fire.
Figure 3.3.3.2b illustrates failure of a plywood panel within the wheel track.

Figure 3.3.3.2a – Abrasion of wearing surface Figure 3.3.3.2b – Failure of plywood deck panel
3.3.3.3 Longitudinal decking
A relatively uncommon form of timber decking consisting of transoms and longitudinal decking has
been used in the past.
The transoms should extend across a minimum of three beams unless designed especially for simple
spans. They should be firmly bolted to the beams and all bolts should be regularly checked.
Longitudinal decking should be laid in long lengths and should be securely bolted to the cross beams
at their ends and at alternate intermediate transoms. This is done to stop flexing of the longitudinal
decking under load, and reducing the pulling motion that shears the bolts through the ends of the
longitudinal decking planks, which is a commonly occurring problem.
Longitudinal decking should be laid with the heartwood down to prevent it rotting and splitting at the
centre, or possibly curling up at the edges.
As the timber shrinks and dries out gaps will form between the planks and jacking of the deck may be
required to close up the gaps with insertions of thin sections. This is especially important on bridges
used by cyclists, and timber bridges should be signed to warn cyclists of the possible dangers when
crossing the bridge.
3.3.3.4 Steel trough decking
Many timber bridges now have steel trough decking replacing the timber decking. The troughs were
initially filled with premix asphalt or mass concrete to a level of approximately 50 mm above the top of
the trough sections. Neither of these infills has performed well as both are porous, permitting water
entry to the trough decking. Compaction of bituminous infill under traffic loads occurs and
approximately two to five years after opening (depending on traffic volumes and loads), the infill
should be resurfaced to regain both longitudinal grade and lateral crossfalls. It is vital with this type of
decking to maintain a crack free surface with good drainage to remove all surface water from the deck,
so that it will not seep through the infill and lay in the steel trough causing corrosion to occur. Some
trough sections were tack welded along their joints whilst others have been bolted or screwed
together. A check should be made of the joining arrangements in case the trough sections are tending
to spread under load. If this problem is occurring, it will normally be reflected in the road surface above
as an area of heaving, dips or even pot holes in the infill or areas of heavy cracking. They are signs

that the trough sections are deflecting excessively under load or are not being effectively held down to
the girders. Refer to Figure 3.3.3.4a and Figure 3.3.3.4b for commonly visible defects.
Concrete infill with mesh reinforcing over the trough decking has been the most successful infill
material used. In addition, where trough decking is in very poor condition, a number of bridges have
had a structurally reinforced deck poured, using the trough profile as permanent formwork.
Figure 3.3.3.4a – Corrosion of joints between Figure 3.3.3.4b – Cracking and perforation of steel
trough sections trough decking
3.3.4 Kerbs, posts and railing
Visual inspection should be conducted of the kerb condition and bolting to the decking or beams. The
kerbs should be firmly held in place as the barrier posts rely on this for strength of support.
The endposts may be round timber and suffer from settlement, splitting, sap rot, base rot, piping, and
top rot due to weathering. If the post can be moved by hand it is usually a sign that replacement is
required, though in some cases this can be caused simply by a lack of embedment in the fill.
Inspection usually consists of visually inspecting the bolting, paintwork and damage caused by
glancing blows from vehicles.
Standard timber rails are mainly used on timber bridges but steel guardrail is also reasonably
common. Connections need to be inspected for rigidity, and paintwork inspected for traffic safety
reasons. With timber rails, rot and splitting may require early replacement of some sections.
3.3.5 Piles
Piles can be classified into two main groups; those which take vertical loads and support headstocks,
and those which take moments such as wingwall piles or stream fender piles. Abutment piles are
required to take both vertical loads and horizontal earth pressure loads.
Areas where rot is most likely to occur are at ground level, normal water level (usually 300 to 600 mm
below waling’s) or around areas of numerous bolt holes such as waling’s and crossbracing.
Piles which take moments are particularly susceptible at ground or normal water level where
maximum stress and suspected rot areas coincide. If pipe rot has been detected in these critical areas
the extent of decay needs to be defined so the length of repair or replacement of the pile can be
determined (refer Figure 3.3.5a).

Care also needs to be taken in determining natural ground level as scour, filling or siltation may have
occurred. If filling or siltation has occurred, the pile may have substantial pipe rot well below the
current ground level. If the pile has rotted out below ground and moving under load, a void will be seen
around the pile. Under load the pile will be seen to visually move. If this occurs in water, ripples will be
seen to emanate from the moving pile. In scoured areas the pile will need to be inspected higher up at
what was originally the ground level.
Piles should be visually checked for areas of rot or splitting in the loaded areas at the top, especially
splits originating beneath the headstocks (refer Figure 3.3.5b).
Where the bridge is submersible, the adequacy of the headstock/pile bolted connection should be
checked. Weakening of the piles above this section due to pile rot may allow the superstructure to
float off. The presence of the top pile strap bolt should also be confirmed.
Termites are a continual problems with timber piles in all areas of the state. The termites can enter the
piles as low as 300 mm below ground, but usually enter via splits in the timber. Their presence can be
seen with dirt galleries in the splits or along the outside of the pile. They may also be encountered
stuck to the probe when testing the pile for rot. The termites eat out runways within the timber and
when probing the test hole it feels as if you are scraping over a lot of thin timber sections.
Piles can often wear away at ground level or at bed level due to the action of abrasive gravels or
sands and this should be checked. The abrasive gravels occur in the mountainous regions and the
wear can usually be seen, but abrasion by sands usually occurs at the mouth of the rivers and is due
to sand movement with the tides. Structures in these locations should have the pile diameters at bed
level checked by divers to ascertain the loss of section.
Figure 3.3.5a – Decay of pile below ground Figure 3.3.5b – Splitting of pile beneath
level headstock

Timber piles in marine situations can also suffer attack from teredo. This attack can occur anywhere
between bed level and mean low tide level. Presence of teredo can be judged from either sacrificial
Oregon timber attached to the pile group, or by smooth runways along the hardwood timber in the
mean low tide area (they may often only attack the softwood) or by small 5 to 10 mm diameter holes in
the piles below water. Teredo will consume the interior of timber piles with damage going completely
unnoticed until failure of the pile below water occurs, hence the importance of early detection.
3.3.6 Waling’s and crossbraces
Waling’s and cross bracing should be visually checked to ensure that the members are adequately
stiffening the piles and providing a rigid frame against the action of the stream and possible debris and
log impact forces. Waling’s are usually encountered 300 to 600 mm above normal water level and give
a good guide as to the relative water level at the time of inspection, i.e. if the water level is too high
then the timber piles should be reinspected when the level drops to normal water level. Waling’s can
also be good guide as to whether scour or silting is occurring at the pier.
3.3.7 Headstocks
Most headstocks on timber bridges consist of sawn timber, approximately 300 mm x 180 mm in a
section. Headstocks consisting of solid hewn sections also exist, but are much less common.
Inspection of headstocks should include the following areas:
• check for presence of termites
• check for top rot due to the presence of wet fill
• check for weathering or end rot
• check for splitting
• check for any rot or separation of headstocks that are spliced at an inner pile
• if the beams are not directly over the piles then the headstocks should be checked for
sagging, indicating they are being overloaded
• check for any settlement of piles causing a sag in the headstocks
• be especially wary of loaded timber overhangs
• check that the headstocks have mechanical support on the piles and are not purely relying on
bolting to transfer their loads (headstock seating may have been removed to allow placement
of pile bracing)
• check all bolting is tight and in place. Severely corroded bolts are to be replaced
• check for loss of section due to excessive cuts in headstock (typically in the vicinity of the
bracing).
3.3.8 Abutments and piers
3.3.8.1 Bed logs and props
Some timber bridges have bed-logs stacked on top of each other to form abutments, whilst others
have props resting on a bed-log to form a relieving abutment in front of the original abutment.
Items to check include:
• pipe rot in main load bearing areas

• load bearing of the timber girders or props on the bed-logs
• check for severe crushing of the bed-logs under loaded areas
• check for excessive splitting or end rot of the bed-logs
• check for leaning of the bed-logs.
Sometimes a timber bed-log may be placed in front of the other bed logs to support the fill on which
the bed-logs bear. These bed-logs do not support the girders but are still important in retaining the fill
and preventing scour beneath the bearing bed-logs.
Props are used to transfer vertical load from suspect piles or suspect abutments and usually bear on
bed-logs or heavy sawn timbers. The props should be inspected for rot if they consist of round or
hewn timber which still has the heartwood within. If the prop is of sawn timber there can be no pipe rot,
but its condition such as end bearing support, connection to bed-log, splitting etc. should be noted.
The prop must be securely attached to the girder or relieving headstock, and capable of taking the
direct load. Stability of the props is also important and any leaning prop must be listed for repair.
3.3.8.2 Headstock on piles
The majority of timber abutments and piers will be of this form. Refer to paragraphs 3.3.5 and 3.3.7.
3.3.8.3 Abutment sheeting, ballast boards and wing sheeting
The abutment and wing sheeting and ballast boards are structural elements. Abutment and wing
sheeting may consist of timber planks or precast reinforced concrete units, placed behind the piles to
hold the embankment fill in place. The inspector should check for rot, cracking, bulging and
undermining by the stream.
Ballast boards can consist of timber sheeting or precast reinforced concrete units. The inspector
should again look for rot, cracking, bulging or breaking out of concrete. Once again, the function of the
member is to adequately retain the embankment fill, and, provided the rot, cracking or bulging is not
too extreme, these members are usually adequate.
3.4 Other structure types
3.4.1 Box culverts
The early type box culverts were cast-in-place and many suffer from cracking and spalling due to lack
of concrete cover or ingress of moisture. Once repairs are required to these structures they tend to be
ongoing problems as the other areas fail due to general dampness through the porous concrete.
A common form of construction in the 1950’s – 1960’s comprised in situ walls supporting reinforced
concrete slabs dowelled into the piers. Failure of these dowels resulting in movement of the deck slab
under load has been observed in a number of these structures.
Precast concrete crown units have been used extensively and have generally been found to perform
satisfactorily. However, in many structures fabricated in the 1960's, where calcium chloride was used
as an accelerator, the reinforcement has corroded severely leading to extensive spalling of the cover
concrete.
Link slabs have been used on multi cell culverts to reduce construction costs and time. The link slabs
take the place of the intermediate row of precast crown units by spanning across the gap between
alternate rows of crown units. The link slabs may be either precast in a casting yard, or cast on top of

the culvert base slab and simply lifted into position as required. No service problems have been noted
with these slabs at present.
Proprietary modular culvert systems have also been adopted on the network. These comprise discrete
wall and roof sections that are designed to be connected through a combination of dowels and a
series of fabricated bolted connections.
Construction tolerances have proven to be a problem and the jointing system should be inspected for
completeness, fit and tightness of bolts. In addition, the panel alignment has also been compromised
in some areas and the structure should be checked for consequential damage such as cracking or
spalling caused by bolts or panels bearing excessively on the panel faces.
3.4.2 Pipe culverts
Early pipe culverts were predominantly of masonry construction, formed from engineering ‘red’ bricks
or similar materials. Where conditions were found to be suitable, the pipe was carved through solid
rock.
The majority of these structures were built around the early 1900’s, and the ones inspected to date
appear to be performing satisfactorily, with no major defects found. However, a number of minor
defects have been identified, such as perished mortar, groundwater infiltration (resulting in limescale
leaching and the passing of fines through the culvert lining) and spalled brickwork, which are
attributable to general deterioration over the life of the structure.
Modern pipe culverts are typically constructed from precast concrete segments or corrugated steel
sections, and may be circular or elliptical in shape.
Pipe culverts should be inspected for the presence of corrosion (metal culverts and reinforcement),
cracks, spalls, line, level and stability of headwalls and wingwalls.
3.4.2.1 Precast reinforced concrete culverts
Precast concrete pipe culverts have been used in Queensland for over 50 years. Currently there are
some 25,000 concrete pipe structures recorded in the Structures Information System (approx. 150
major culverts, remainder are minor culverts).
Potential defects of most concern relate to cracking of the pipes. Cracking in pipes can compromise
the strength, durability and function of the pipe over the design life. Cracked concrete allows water/air
through the cracks and will trigger or speed up deterioration processes such as carbonation of the
protective concrete cover and actual corrosion of the reinforcing steel. Once the steel starts to
corrode, spalling of the surrounding concrete occurs resulting in a weakening and eventually
collapsing pipe. Depending on the size of pipe, major defects can cause loss of the road function and
can pose significant safety hazards to road users.
Cracking may be initiated by any number of reasons such as:
• incorrect design
• inadequacies in manufacture
• incorrect handling/stacking or transportation
• incorrect installation
• overloading during construction.

Figure 3.4.2.1a and Figure 3.4.2.1b illustrate examples of cracking and spalling in precast concrete
pipe culverts.
Figure 3.4.2.1a – Cracking of pipe walls Figure 3.4.2.1b – Loss of cover/spalling concrete in
pipe crown
3.4.2.2 Buried corrugated metal culverts
Buried corrugated metal (BCM) culvert structures are recognised worldwide as a high risk structure,
comprising a thin wall section of steel or aluminium that is prone to corrode longitudinally at the top of
the wetted area or in the invert. If left unattended the corrosion can lead to perforation of the
corrugations. Figure 3.4.2.2a and Figure 3.4.2.2b illustrate the typical location of corrosion while
Figure 3.4.2.2c and Figure 3.4.2.2d show examples of perforated culverts.
Aluminium culverts are known to have greater corrosion resistance than steel culverts but
performance is sensitive to surrounding soil conditions. Aluminium culverts are more susceptible to
abrasion effects than steel culverts unless suitable protection is provided.
Figure 3.4.2.2a – Typical location of wall corrosion Figure 3.4.2.2b – BCM culvert wall corrosion above
in BCM culvert invert protection

Once a metal pipe has perforated, two failure modes are possible:
• In dry conditions, the soil pressure eventually causes the culvert to shear through and the tube
folds in on itself. The soil above arches and supports the embankment and traffic loads but
gradually settles, creating a dip in the road surface. This gradually increases until it becomes
dangerous, particularly to small vehicles (such as motorbikes) and high speed traffic.
• Heavy rain and associated heavy stream flows in a corroded culvert can rapidly erode the
compacted soil embankment causing voids around the culvert and eventual piping failure.
Where the embankment height is greater than the pipe diameter, soil arching is maintained
until it is destabilised by the formation of a void in the embankment, resulting in the sudden
collapse of the road and the consequential risk of vehicles dropping into the open barrel of a
fast flowing stream.
Figure 3.4.2.2c – Perforation of BCM culvert invert Figure 3.4.2.2d – Perforation of BCM culvert wall
3.4.3 Large traffic management signs
Large cantilever signs, butterfly signs and sign gantries are increasingly prevalent on the network and
constitute major structures in their own right.
Sign and signal gantries either span or cantilever over part of the carriageway.
The consequences of any failure or partial failure of one of these structures has the potential to cause
significant disruption to the network and potential loss of life.
High wind forces on signs and other attachments will produce large twisting forces on supports,
connections, columns and base connections. Furthermore they are also susceptible to wind induced
vibrations with associated potential fatigue related defects (particularly in hold-down bolts and welded
connections) which could lead to collapse of the structure onto trafficked lanes.
Key areas for inspection include:
• missing, loose or damaged nuts/bolts
• cracked welds
• butt welds at structural connections
• corrosion

• splits or ruptures in columns and stiffeners
• impact damage
• tilting columns
• crushed/missing mortar beneath base plates
• exposed levelling nuts beneath base plate (levelling nuts should not be engaged in carrying
load after mortar has been placed)
• base plates or other steelwork which has been incorrectly (i.e. not in accordance with the
drawings) encased in grout or concrete (any affected components will need to be exposed to
determine the extent of any corrosion)
• cracking/spalling of concrete around base plates.
Nuts on hold-down bolts should have been checked at installation for tension and marked. The
inspector should check the marks and note if there has been any movement or loosening of the nuts.
3.4.4 Retaining walls
Retaining walls are any structure where the dominant function is to act as a retaining structure for
embankments or fill slopes be they above, below or either side of the carriageway.
A variety of structural forms are employed across the network including:
• Gravity wall – resist earth pressures through own self weight. Examples of gravity walls
include:
− mass concrete monolithic walls
− unreinforced masonry walls
− gabion baskets (i.e. woven steel wire baskets filled with stone)
− crib walls (reinforced concrete or timber crib units filled with free draining material)
− reinforced soil/mechanically stabilised earth walls (soil nailing or anchoring using steel or
geotextile reinforcement to stabilise retained material).
• Cantilever on foundation wall – comprise a vertical wall rigidly fixed to a horizontal foundation
slab. Horizontal earth pressures are transferred to the foundation (primarily in bending). These
types of wall are typically constructed of reinforced concrete.
• Embedded retaining wall – these types of wall are similar to cantilever on foundation walls with
the exception that there is no horizontal foundation. Retention of fill is achieved through depth
of embedment. Examples of embedded retaining walls include:
− sheet piles. driven steel, concrete or timber piles
− insitu concrete bored pile walls. Can be contiguous or secant piled walls.
• Diaphragm walls – insitu or precast reinforced concrete walls placed into a narrow trench
stabilised with bentonite slurry. The bentonite slurry is displaced during construction.
• Soldier pile walls – comprise driven (steel, timber or precast concrete) or insitu concrete
vertical piles installed at regular centres with sheeting spanning between the piles. Sheeting
may be steel, precast concrete or timber.

Defects/deterioration associated with the various wall types described above can be attributed to the
construction material (s) or stability of the retained (or founding) material.
Material related defects will typically be as described in Section 2. Any connections/fixings utilised in
the wall construction type must also be considered, with particular attention paid to tightness,
corrosion and missing or incorrectly installed fixings. Embedded materials not accessible for
inspection (e.g. soil nails, anchors, etc.) may require specialist inspection to evaluate condition unless
consideration was given at time of design/construction (e.g. inclusion of additional ‘sacrificial’ nails
able to be removed for inspection or installation of load cells to monitor tension in embedded
components).
Indicators of potential issues with stability of retained or founding material can include:
• cracking/slumping of carriageway or shoulder parallel to the retained face may indicate

settlement, outward movement or loss of retained material
• change in alignment of the top face of the retaining wall or guardrail/barrier
• change in angle of the retaining wall indicating rotation of wall
• erosion or removal of material to front face of the retaining wall
• blocked/inadequate drainage (weep) holes to relieve pore pressure behind walls.
In addition to the above, the impact of any proposed change in land use adjacent to a retaining
structure (e.g. widening or realignment of carriageway (even temporarily to facilitate maintenance)
must be carefully considered as the effects may not have been considered at the design stage.
3.5 Causes of deterioration not related to construction materials
A number of components need to be inspected which are not related to defects in construction
materials used in a structure but which, if not observed or maintained, could be a cause of future
deterioration.
3.5.1.1 Deck joints
Various types of expansion joints have been used in the past to cater for movements of bridge
superstructures. Early bridges had small simply supported spans and hence only small movements
needed to be catered for.
These joints included materials with small compressions such as cork, bituminous impregnated
fibreboard, butyl impregnated polyurethane foam, styrene and foam strips. Asphalt, rubberised
bitumen or polyurethane were often poured over the top in an effort to seal the joint from moisture
penetration. Many of these joints failed to seal due to the joint material debonding or being inelastic. If
the sealant was placed too high in the groove, traffic tended to crack the sealant and rip it out.
For small expansion joints a repair being used at present is to pour a polymer modified bitumen
(Mobil N345 or ‘megaprene’) into the joint with a thickness of approximately 20 mm. Care must be
taken to ensure overfilling does not occur and a 6 to 10 mm depth from the top is required so that
traffic will not rip the material out when expansion of the deck occurs. This product has better elastic
properties than the previously used rubberised bitumen. Reasonable performance has been found
though it tends to expand greatly when heated, and a slightly stiffer and less elastic product would be
a better option.

As spans increased, so did the width of expansion joint, and compression seals were introduced to
cater for the increased range of movements expected. The earliest seal used was the neoprene hose
but this product proved to be inelastic and often fell through the joint leaving it completely open.
‘Wabo’ compression seals were then used firstly between steel angle nosings, and currently between
fibre reinforced concrete nosings. One problem with this seal is that it can tend to debond from the
concrete deck or steel and gradually work its way to the top of the joint where traffic damages the seal
or, in some cases, rips the seal completely out. Steel angle nosings are also susceptible to damage
through high impact loads imposed by vehicle tyres, especially where dry packed mortar has been
rammed beneath the angle. This mortar breaks up under impact and the resulting loss of support
leads to failure of the bars anchoring the plates into the concrete deck. The angles then start rattling
and moving under load which cracks the bitumen at the edge of the angle.
‘Alustrip’ expansion joints are now commonly used and these consist of a thin neoprene sheet
anchored into aluminium blocks which in turn are bolted down to the deck. These blocks can break
loose if bolting was provided via cored holes rather than bolts cast into the deck. The seals also can
become damaged and require resealing.
On large span bridges steel finger plates and steel sliding plate joints have been used. These joints
have never offered a seal to moisture penetration and the sliding plates continually vibrate loose
causing a danger to traffic. They have been superseded by heavy duty rubber joints such as
‘Transflex’, ‘Waboflex’ and ‘Felspan’. A problem with these joints is possible debonding of the metal
and rubber sections.
Epoxy mortar nosings were used in the past to support the joints but these thin sections, cast after the
deck, only broke up under repeated impact loads.
On bridge decks with small movements and a large asphalt cover a product called ‘ThormaJoint’ has
been used. This joint consists of a hot mix of selected stone and an elastomer modified bitumen
binder, and looks like a strip (approximately 500 mm wide) of very dark asphalt. Performance is
generally very good where it has been used, and provides improved ride over the joint.
3.5.2 Bearings
A large number of different bearing systems have been used in the past and only the more common
types will be discussed here. The first precast and cast insitu beams usually sat on the headstocks
with the only form of bond breakers between the two being a layer of clear grease, a sheet of malthoid
or in some cases a sheet of lead. Locating dowels from the headstock were used but these have
simply tended to break out the ends of the concrete beams, or in some instances, break out the top of
the crosshead beneath the beam due to movement and edge loadings.
Mortar pads have had considerable use in the past and are generally found in good condition, though
some rammed mortar pads beneath the beams tend to crack badly and spall the mortar.
Also to be found on many bridges are steel base plates on which rest the smaller steel bearing plates
of the beams. Sometimes a phosphor bronze sliding plate may be inserted between the steel plates to
aid in longitudinal movement between them.
Cast iron bearing blocks with sliding plates or pins, mild steel rollers and rocker bearings have also
been used where large steel beam spans are present. Dirt, grit and corrosion due to moisture are a
continual problem with these bearing types, with many rollers and rockers being completely seized up
by corrosion.

Large span, heavy concrete bridges such as box girders can be supported on pot bearings or bearings
with a P.T.F.E. (teflon) sliding disc. These are specialised high load bearings but the position of the
P.T.F.E. strip should be noted, especially as it can tend to be squeezed out by vibration. Excessive
rotations of the bearings should also be noted.
The most common bearing in use today is the elastomeric bearing in two different forms; as a 25 mm
thick neoprene pad, or as a larger depth bearing with metal shim plates between elastomeric layers.
The thinner bearing strips usually support small span beams and have few problems although if the
bearing pedestals are poorly constructed then some areas of the pads may not carry load. The larger
bearings can suffer from irregular bulging and shearing of the elastomeric/metal shim surface if poorly
designed or manufactured. Rotation and shear of the bearings can occur with bridge movement, and
this can cause lift-off of the bearings at the edge, and hence over-stressing at the opposite edge.
A common problem associated with large bearings is poor uneven pedestal construction resulting in
significant areas of the bearing pads being unstressed.
Creep, shrinkage and elastic shortening due to post-tensioning in some structures cause shear
stresses on the bearings. These bearings should be reset by jacking the structure, but this is rarely
done unless shear is excessive. Slippage of the bearings can also occur in girder structures where
retainers on the sole plates were not provided, with bearings working their way forward from the
support area.
3.5.3 Damage due to accidents
The most common components affected by vehicular impact are barriers, kerbs, footpath slabs and
end posts which can be severely abraded, spalled or damaged. Damage is usually self-evident.
Other areas that can be affected are columns, outer beams or soffits of overpass structures. Steel
beams are particularly susceptible to damage from over-height vehicles which can cause severe
deformations to the bottom flange or web of the member.
Bridges over navigable waterways may also have damage to pier columns and pile caps due to impact
of vessels. The damage may be sufficient to cause major structural damage or movement of the
column requiring an assessment of the structural adequacy of the bridge, or cause abrasion and
spalling of concrete which can result in eventual corrosion of reinforcement.
3.5.4 Drainage
Ineffective drainage may affect a structure in several ways:
• Standing water in the carriageway which may create a serious traffic hazard.
• Debris carried by drainage flows will build up in areas, retain moisture, and promote corrosion.
• Leakage through deck joints and cracks will cause unsightly staining of beams, piers and
abutments.
• Water flowing uncontrolled over concrete or steel surfaces or bearings below deck level may
result in corrosion or unsatisfactory performance of bearings.
• Inadequate collection of drainage from decks and approaches can cause erosion, piping and
washout or scour of the approach embankment and batter slopes along with undermining of
foundations, particularly in areas where flows are concentrated at the end of the bridge around
the end post and at ends of kerbs or service ducts. These areas should be inspected
particularly after heavy rain or flooding.

• Inadequate or blocked weepholes in retaining structures can result in a build-up of pore water
pressure, increasing lateral pressures on the wall.
3.5.5 Debris
The build-up of debris on the upstream side of structures can cause the following adverse effects:
• Impose lateral loads on a bridge superstructure during flooding for which it was not designed.
• Cause blockage of the waterway during flooding which can exacerbate problems of scour,
undermining of foundations, flooding and in extreme cases total blockage and diversions of
the watercourse.
• Development of permanent ‘obstructions developing within the waterway.
Build-up of debris is dependent on upstream catchment conditions/use and its impact is usually most
severe in structures with small openings or low freeboard.
Additionally, the build-up of debris below a structure may become a fire hazard, increasing the risk of
fire damage to piles and headstocks.
3.5.6 Vegetation
Uncontrolled and excessive growth of vegetation beneath, adjacent to or on a structure can have both
positive and negative consequences. In the case of bridges and culverts, the presence of vegetation is
typically negative as it can result in:
• fire hazard
• blockage of waterway
• retention of moisture around key components (bearings, girders, headstocks, etc.)
• build-up of leaf litter across decks will block scuppers and promote decay
• root ingress and growth can displace and damage components
• limited access to and poor visibility of structure components
• limited sight distances across structures
• overhanging limbs pose a hazard to road users.
For retaining structures, the presence of vegetation on the up and down slope will typically contribute
to slope stability as well as improving resistance to erosion however large trees can become unstable
and cause substantial damage if they fail. Vegetation growth on retaining structures limits access and
visibility of components and, as for bridges and culverts, root ingress and growth can displace/damage
components.
3.5.7 Waterway scour
Scour in watercourses and drainage paths has the potential to cause significant damage to the
environment and engineering infrastructure.
Scour is the erosive action of flowing water, resulting in the removal, and subsequent deposition, of
material from the bed and banks of streams and from around the piers and abutments of bridges.
Scour can result in a general lowering (degradation) or raising (aggradation) of the river bed, lateral
erosion of river banks or the development of localised scour holes around piers/piles and abutments.

It is a requirement of Level two inspections to capture the waterway profile for bridges and culverts
crossing waterways. This allows for the monitoring of general waterway behaviour over time.
Indications of recent ‘fresh’ scour activity include:
• loss of vegetation/exposed roots on waterway bank (refer Figure 3.5.7a)
• exposed piles (refer Figure 3.5.7b and Figure 3.5.7c).
• undermining/voiding to toe of bank or provided batter protection
• evidence of batter protection settlement such as cracking in rigid protection or slumping in

flexible/semi-rigid protection (refer Figure 3.5.7d)
• loss of abutment batter protection
• undermining/voiding beneath abutment/piers
• accumulation of loose sediment adjacent river banks around piers (the latter may be indicative
of localised scour holes being backfilled with loose material as water levels recede).
Degradation and localised scour can result in progressive settlement or movement of abutments,
piers, culverts and any other structure in or adjacent to the waterway which, if not rectified can lead to
total failure of the structure.
Figure 3.5.7a – Example of recent bank erosion Figure 3.5.7b – Localised scour around pier
pile cap and piles
Figure 3.5.7c – Localised scour around pier Figure 3.5.7d – Settlement of rigid batter
piles and debris build-up protection

3.5.8 Movement of the structure
Unanticipated movement of structures may result from:
• general scour of the stream bed in the vicinity of the structure
• local scour of the stream bed at piers or abutments
• movement of the ground due to land slips at or around the structure
• excessive earth pressure caused by movements or settlements of retained fill
• founding of structures on expansive clays
• collisions, in the case of bridges over navigable waterways, roads, or railways
• ‘freezing’ up of bearings or expansion joints.
Movements can usually be detected by observing:
• total closure or excessive opening of deck expansion joints
• bearing or jamming up between the end of the superstructure and abutment ballast wall with
associated cracking and spalling
• cracking or excessive settlement of the approach embankments or heaving at toe
• undermining of foundations
• rotation of columns, piles, walls or adjacent poles, fences, etc.
It is important to report any of the above defects if they are observed as any movement could continue
over a period of time and comparisons with past and future inspections is important to assess whether
it is continuing, seasonal or has ceased.
3.5.9 Condition of approaches
The purpose of the approach embankment is to provide a stable transition between the bridge and
adjacent pavement. Often it is also required to provide horizontal, and sometimes vertical support for
the abutment foundation.
The most common defect of approach embankments is usually excessive settlement adjacent to the
bridge abutment which causes unsatisfactory riding quality and possible damage to deck and
expansion joints.
This can be caused by poorly compacted embankment, and or continuing settlement of the underlying
ground. Instability of ground and embankment can also be observed in its early stages by excessive
settlement or movement of the embankment.
It should be noted that while the subsidence behind bridge abutments is often attributed to settlement
of embankment fill the defect may often be caused by other factors including:
• settlement or rotation of walls which allows loss of embankment material generally as a result
of leaching of fines
• settlement of infill panels or backing slabs, which generally occurs as a result of softening of
moisture susceptible founding material or following scouring of the footing
• erosion, piping, washout and scour of the embankment, particularly after heavy rain or
flooding, or due to inadequate or blocked drainage.

4 References
1. Ministry of Transportation, Ontario (1989). Ontario Structure Inspection Manual. Highway
Engineering Division
2. Austroads (1991). Bridge Management Practice
3. Transit New Zealand (1991). Bridge Inspection and Maintenance Manual
4. Austroads (1991). Guide to Bridge Construction Practice
5. Austroads (2009). Guide to Bridge Technology Part 2: Materials
6. Austroads (2009). Guide to Bridge Technology Part 4: Design Procurement and Concept
Design
7. Austroads (2009). Guide to Bridge Technology Part 6: Bridge Construction
8. Austroads (2009). Guide to Bridge Technology Part 7: Maintenance and Management of

Existing Bridges
9. Bootle, K. R. (1983). Wood in Australia, Types, Properties and Uses. McGraw Hill: Sydney
10. CSIRO, Division of Building (1975). Effect of fire on Timber Engineering. Melbourne, Lectures
given by Officers of CSIRO Div. of Building Research Highett
11. McGregor, K. (1991). Guidelines for Timber Bridge Inspection, Maintenance & Repair.
VicRoads
12. VicRoads (2014). Road Structures Inspection Manual, Principal Bridge Engineer’s section,
VicRoads Technical Services, VicRoads
13. VicRoads (2011). Technical Note 102 Fire Damaged Reinforced Concrete – Investigation,
Assessment and Repair, VicRoads Technical Services, VicRoads

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Structures Inspection Manual, Transport and Main Roads, September 2016

Structures Inspection Manual, Transport and Main Roads, September 2016 i

Figure 2.2.2a – Example ASR crack pattern in pier column ................................................................... 5

Figure 2.2.2b – Example ASR crack pattern in abutment wall ................................................................ 5

Figure 2.2.2c – Example ASR crack pattern in pier headstock ............................................................... 5

Figure 2.2.3.1b – Plastic shrinkage cracking in bridge deck ................................................................... 8

Figure 2.2.3.1c – Plastic settlement crack in slab ................................................................................... 8

Figure 2.2.3.2b – Typical flexural cracks at mid-span of girder............................................................... 9

Figure 2.2.3.2c – Crack/separation in abutment wall due to differential settlement................................ 9

Figure 2.2.3.2d – Shear crack in girder adjacent to support ................................................................... 9

Figure 2.2.3.3 – Accurate measurement of crack width ........................................................................ 10

Figure 2.2.4a – Spalling of concrete at ends of deck units ................................................................... 11

Figure 2.2.4b – Spalling to front face of headstock ............................................................................... 11

Figure 2.2.4c – Spalling of slab soffit .................................................................................................... 11

Figure 2.2.4d – Corner spalling of square pile ...................................................................................... 11

Structures Inspection Manual, Transport and Main Roads, September 2016 ii

Figure 2.2.6d – Discharge through cracks in concrete surface ............................................................. 13

Figure 2.2.6e – Concrete honeycombing .............................................................................................. 13

Figure 2.2.6f – Abrasion of concrete ..................................................................................................... 13

Figure 2.2.7a – Concrete scaling .......................................................................................................... 14

Figure 2.2.7b – Concrete disintegration ................................................................................................ 14

Figure 2.3.1a – Mild surface corrosion .................................................................................................. 16

Figure 2.3.1b – Severe corrosion and loss of section ........................................................................... 16

Figure 2.3.1c – Pitting of steel ............................................................................................................... 17

Figure 2.3.1d – Corrosion of steel by SRB ............................................................................................ 17

Figure 2.3.2a – White deposit on zinc metal spray ............................................................................... 18

Figure 2.3.2b – Failure of paint system over galvanising ...................................................................... 18

Figure 2.3.2c – Blistering of paint system ............................................................................................. 18

Figure 2.3.2d – Flaking of paint system ................................................................................................ 18

Figure 2.3.3a – Buckling of gusset plate ............................................................................................... 20

Figure 2.3.3b – Impact damage to steel beam ...................................................................................... 20

Figure 2.3.4a – Fatigue cracking in web ............................................................................................... 21

Figure 2.3.4b – Cracking in welds ......................................................................................................... 21

Figure 2.4.1a – Fungal fruiting body and decay of girder ...................................................................... 25

Figure 2.4.1b – Decay pocket in girder ................................................................................................. 25

Figure 2.4.2a – Termite nest on bridge pile........................................................................................... 26

Figure 2.4.2b – Termite gallery on pier headstock ................................................................................ 26

Figure 2.4.3a – External damage to timber pile from shipworm............................................................ 28

Figure 2.4.3b – Timber piles subject to Sphaemora attack ................................................................... 28

Figure 2.4.4.1a – Splitting in timber pile ................................................................................................ 29

Figure 2.4.4.1b – Splitting in timber headstock ..................................................................................... 29

Figure 3.3.3.2a – Abrasion of wearing surface...................................................................................... 42

Figure 3.3.3.2b – Failure of plywood deck panel .................................................................................. 42

Figure 3.3.3.4a – Corrosion of joints between trough sections ............................................................. 43

Figure 3.3.3.4b – Cracking and perforation of steel trough decking ..................................................... 43

Figure 3.3.5a – Decay of pile below ground level ................................................................................. 44

Figure 3.3.5b – Splitting of pile beneath headstock .............................................................................. 44

Figure 3.4.2.1a – Cracking of pipe walls ............................................................................................... 48

Figure 3.4.2.2a – Typical location of wall corrosion in BCM culvert ...................................................... 48

Figure 3.5.7a – Example of recent bank erosion .................................................................................. 55

Figure 3.5.7d – Settlement of rigid batter protection ............................................................................. 55

Structures Inspection Manual, Transport and Main Roads, September 2016 iv

• Settlement of embankments may affect the substructure, appearing as depressions in the

Based on concrete defects described in Ontario Ministry of Transportation, Ontario Structure

Structures Inspection Manual, Transport and Main Roads, September 2016 1