D.SH Final Structure Report

Consultancy Service for Detailed Engineering Draft Structural Report
Design of Yabelo - Metagefersa- Shakiso

Design and Build Road Project Contract 3:
Dermi- Kenticha - Shakiso
Ethiopian Roads Authority Dec , 2021
Table of Contents
1 STRUCTURES DESIGN...................................................................................................7
1.1 General...........................................................................................................................7
2 SITE INVESTIGATION...................................................................................................8
2.1 Criteria of Assessment and Inventory........................................................................8
2.2 Drainage Structures Inventory...................................................................................9
2.3 Minor Drainage Structures Inventory......................................................................10
2.3.1 Observed Damages on Minor Structures.........................................................10
2.3.2 Recommendations on existing Minor Structures.............................................12
2.4 Drainage Major structures Inventory.......................................................................12
2.4.1 Details of Bridge..............................................................................................12
2.4.2 Recommendation on Existing Major Structures..............................................13
2.5 Strength Evaluation of existing structure.................................................................13
3 STRUCTURES DESIGN STANDARED AND CRITERIA..........................................14
3.1 Structure Design Standards......................................................................................14
3.2 Structure Type Selection..........................................................................................14
3.2.1 Major Drainage Structure Type Selection........................................................14
3.2.2 Minor Drainage Structure Type Selection.......................................................14
3.2.3 Pipe Class.........................................................................................................15
3.2.4 Pipe Bedding....................................................................................................15
3.3 Materials properties..................................................................................................15
3.3.1 Concrete...........................................................................................................15
3.3.2 Reinforcement..................................................................................................16
Walabu Construction Share Company as Contractor and
G and Y Engineering Consult plc. As a Design Partner. i

3.3.3 Stone Masonry.................................................................................................16
3.3.4 Gabions............................................................................................................17
4 DESIGN METHOD.........................................................................................................18
4.1 Superstructure Design..............................................................................................19
4.2 Substructure Design.................................................................................................19
5 CULVERT DESIGN........................................................................................................20
5.1 Culvert Design Standards.........................................................................................20
5.1.1 General.................................................................................................................20
5.1.2 Dead Loads.......................................................................................................20
5.1.3 Live Loads........................................................................................................20
5.1.4 Distribution of Wheel Loads through Fills......................................................21
5.1.5 Design Methodology of Culverts.....................................................................21
5.1.6 General Design Criteria and Loadings.............................................................21
5.1.7 Materials...........................................................................................................22
5.1.8 Concrete...........................................................................................................22
5.1.9 Reinforcement..................................................................................................23
5.1.10 Stone Masonry.................................................................................................23
5.1.11 Culvert Sizes Shape and Layout......................................................................23
5.1.12 Material Selection............................................................................................24
5.2 Proposed types of cross drainage structures.............................................................24
5.2.1 Reinforced Concrete Pipe Culverts..................................................................25
5.2.2 Selection Between Slab and Box Culverts.......................................................30
5.3 Components of Culverts...........................................................................................32
G and Y Engineering Consult plc. As a Design Partner. ii

5.3.1 Headwalls:........................................................................................................32
5.3.2 Inlet and Outlet Structure:................................................................................32
5.3.3 Aprons and cut-off walls at inlet and outlet:....................................................33
5.3.4 Erosion Protection:...........................................................................................33
5.3.5 Culvert Skewness:............................................................................................33
5.3.6 Construction Method and Materials.................................................................33
6 BRIDGE DESIGN...........................................................................................................34
6.1 Bridge Loading.........................................................................................................34
6.1.1 Permanent Loads..................................................................................................34
6.1.2 Transient Loads................................................................................................34
6.1.3 Dynamic Load Allowance................................................................................35
6.1.4 Secondary Live Loads......................................................................................35
6.1.5 Vehicular Live Loads (LL)..............................................................................35
6.1.6 Pedestrian Load................................................................................................36
6.1.7 Environmental Effects......................................................................................37
6.2 Materials...................................................................................................................37
6.2.1 Reinforced Concrete.........................................................................................37
6.3 Major Drainage Structures Design...........................................................................38
6.3.1 General.............................................................................................................38
6.3.2 Span Determination..........................................................................................39
6.3.3 Superstructure Design......................................................................................39
6.3.4 Sub structure Design........................................................................................40
6.4 Geotechnical Investigation.......................................................................................40
G and Y Engineering Consult plc. As a Design Partner. iii

6.5 Miscellaneous Design..............................................................................................41
6.5.1 Bridge Railing..................................................................................................41
6.5.2 Bridge Bearings................................................................................................41
6.5.3 Deck Drains......................................................................................................41
6.5.4 Deck Joint Seals...............................................................................................41
6.5.5 Approach Slabs................................................................................................41
List of Tables
G and Y Engineering Consult plc. As a Design Partner. iv

Table 3-1 :- Classes of concrete used for minor and major culverts.......................................16
Table 3-2 :- Classes of concrete used for minor and major culverts........................................16
Table 4-1 Loads for which a minimum value of i is appropriate............................................18
Table 4-2 Resistance Factors...................................................................................................19
Table 5-1:- Design criteria for Culverts...................................................................................21
Table 5-2Classes of concrete used for culvert design..............................................................22
Table 5-3: Grades of reinforcement steel for structure design.................................................23
Table 5-4: Summary of Minor Structures................................................................................24
Table 5-5: List of Proposed Pipe Culverts...............................................................................25
Table 5-6: List of Proposed box Culverts................................................................................30
Table 6-1 Structural Recommendation of bridge @ 174+950.................................................39
List of Figures
G and Y Engineering Consult plc. As a Design Partner. v

Figure 2-1 Silted Pipe Culvert at station 188+071...................................................................10
Figure 2-2 Silted Double Pipe Culvert at station 170+723......................................................11
Figure 2-3 Clogged Pipe Culvert @ Station 174+648............................................................11
Figure 2-4 Town Section Pipe Culvert @ Station 241+700..................................................12
Figure 2-5 Bailey bridge at station 174+980...........................................................................13
Figure 6-1 Design Truck Load.................................................................................................36
Figure 6-2 Design Tandem Load.............................................................................................36
LIST OF APPENDIX
Appendix A: Pipe and Box Drawings and schedules
Appendix B: Standard Drawings for Minor structures
Appendix C: Response to Comment
G and Y Engineering Consult plc. As a Design Partner. vi

Dermi- Kenticha - Shakiso (70+371km)
Ethiopian Roads Authority Aug, 2021
1 STRUCTURES DESIGN
1.1 GENERAL
Structures in road projects mainly consist of drainage structures and retaining walls for stability
of slopes. They are one of the most important elements of road construction. The serviceability
of a road is highly influenced by the absence of proper drainage structures and lack of properly
located stabilizing structures. They mainly include culverts, bridges, energy dissipation
structures and retaining walls. Highway Drainage facilities are designed to convey predetermined
discharges in order to avoid a significant flood hazard on the road. The hydrological and
hydraulic analysis for this project has been conducted through careful examination, review and
analysis of the relevant hydro-metrological data, topographical maps aerial photographs and
other imageries. Accordingly, there is 1 major structure and 124 minor structures in this road
project. Of these, there are 24 Box culverts and 100 reinforced concrete pipe culverts.
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alabu Construction Share Company as Contractor and
G and Y Engineering Consult plc. As a Design Partner 7
2 SITE INVESTIGATION
Field investigation was carried out on the project road and found that there are some minor
drainage crossings and one major structure is identified. The major purposes of this site visit are:
 To make an assessment of existing drainage structures,

 To collect data about physical characteristics of structures crossing site,
 To select safe and economical structure type
 To select safe and economical protection works (where it is required),
 To became familiar with the project site,
 To make discussion with the residents to collect appropriate information,
2.1 CRITERIA OF ASSESSMENT AND INVENTORY
The condition of existing structures has been assessed using the criteria outlined below.
 Geometrical Adequacy: The geometrical aspect of the drainage structure with respect to
horizontal and vertical alignments of the approach road as per ERA standard,
 Functional Adequacy: This deals with required carriage width, space provision of crash
barrier, foot path and railings.
 Structural Adequacy: This must deal with structural integrity of the existing structures,
(loading, distress, damage etc)
 Hydrology/Hydraulics Adequacy: This must deal with sufficiency of the existing opening
to allow the maximum design flood, scouring and any damage resulting there from.
In order to assess as per the criteria outlined above, inventory has been carried on each of the
major and minor structures as follows:
 Location and reference name,
 Structure Type and span,
 Relevant dimension such as overall opening length, clear span, overall width, size of
vent,
 Type of construction materials used,
 Alignment of structure straight or skew,
 Type of protection works provided if any for the embankment at the approach and at the
underside riverbed.
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Moreover, the inventory has also focused on the following:

 A detailed inspection of all structures
 The Concrete elements of the bridges were checked for deflection, cracks, rust staining,
exposed reinforcement etc.
 The Condition of the deck slab, T-beam, bearings are noted
 The abutments, wing walls and piers were inspected for settlement cracks, movement and
scour.
 Changes of river course and formation of eddies around the substructure were observed.
 The road alignment and the course of the river at the location of the bridge recorded.
 The span, width of carriageway and other dimensions of the structural elements were
recorded for assessment of load carrying capacity of the bridge.
2.2 DRAINAGE STRUCTURES INVENTORY

Site information was recorded for the existing bridge on the Yabelo - Metagefersa- Shakiso
Design and Build Road Project Contract 3: Dermi- Kenticha - Shakiso (70+371km) Road
upgrading project. The data comprises details of the structure types, construction materials,
major dimensions, clearances, height of substructure etc.
An appraisal of each structure was carried out to determine the condition of each structure with
respect to serviceability and user safety. A standard inspection format has been used in listing all
the elements of the structure and all the common defects encounter. A duly qualified inspector
experienced in structure design and maintenance and rehabilitation works has completed the
forms.
The inspection is being used as the basis for proposing the maintenance and rehabilitation
measures to be implemented during the construction phase. The following are the summarized
investigation of existing structures.
2.3 MINOR DRAINAGE STRUCTURES INVENTORY
2.3.1 OBSERVED DAMAGES ON MINOR STRUCTURES
Existing minor drainage structures of the project is composed of 9 pipe culverts and each culvert
was inspected for defects. The viability of retaining or replacing of existing culverts is being
considered. Based on site investigations, some of the typical problems and findings associated
with these culverts include:-
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 Most of the culverts are silt up

 Some of the culverts are covered by vegetation at outlet
 Embankment erosion at inlet and outlet
 Insufficient hydraulic capacity and overtopping,
 Deterioration due to ageing,
 Scouring on both outlet and inlet side of the structure,
 Structures not properly aligned with the flow line of the stream,
 Structures not satisfying the design standard of the projects,
The following photographs illustrate typical site conditions of existing minor drainage structures
Figure 2-1 Silted Pipe Culvert at station 188+071
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Figure 2-2 Silted Double Pipe Culvert at station 170+723
Figure 2-3 Clogged Pipe Culvert @ Station 174+648
Figure 2-4 Town Section Pipe Culvert @ Station 241+700
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2.3.2 RECOMMENDATIONS ON EXISTING MINOR STRUCTURES
From detailed investigation, the design team has made a recommendation to replace all existing
pipe culvert structures in due consideration of hydrology and hydraulic analysis result and
structural condition of existing structures.
2.4 DRAINAGE MAJOR STRUCTURES INVENTORY
2.4.1 DETAILS OF BRIDGE
There is one existing bridge along the project route and this bridge is a Bailey bridge with a
single span of 40m. The bridge is geometrically unfit, structurally unsound and therefore, it has
to be replaced with a new one.
Figure 2-5 Bailey bridge at station 174+980
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2.4.2 RECOMMENDATION ON EXISTING MAJOR STRUCTURES
From the investigation, it is advisable that the existing bridge should serve as traffic relief and
the new bridge which is adjacent to the existing one will be the main crossing of the rivers
because it is necessary for the bridge and each of its components to be safe, durable, reliable and
stable. In addition to this, the width requirement is not within the standard of this project.
2.5 STRENGTH EVALUATION OF EXISTING STRUCTURE

Detailed condition survey has been carried first for structures of the road project in view of
checking structural adequacy. Following the condition survey, it is difficult to get the detail as
built drawings for the existing bridges to obtain useful details such as reinforcement detail,
Dimensions of the structure for checking against site measurement, material specification data
and other information to determine the capacity of existing structures.
3 STRUCTURES DESIGN STANDARED AND CRITERIA
3.1 STRUCTURE DESIGN STANDARDS

In accordance with the requirement of Employer’s requirement of the contract agreement, the
detailed engineering design of minor drainage structures of the project is carried out by
employing the following standards.
 ERA 2013 Bridge Design Manual
 ERA 2013 Standard Drawings
 ERA 2013 Drainage Design Manual
 ERA 2013Standard Technical specifications
 AASHTO Bridge Design Specification 2014
 AASHTO Standard Specification for Transportation Materials and Method for Sampling
and Testing, recent edition
3.2 STRUCTURE TYPE SELECTION
3.2.1 MAJOR DRAINAGE STRUCTURE TYPE SELECTION
Selection of bridge type in general is related to economy, Safety, Ease of maintenance and
aesthetics. Depending on the defined channel opening and discharge requirements, the span of
the cross drainage structures are determined on the basis of which are classified as:
 6m-10m Slab Bridge
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 11m-25m Reinforced Concrete Desk Girder Bridge

 25m-45m Box Girder Bridge
For multiple span bridges we can use the combination of the above bridge type and select the
most suitable span configuration among different possible alternatives based on selection of
bridge type criteria.
3.2.2 MINOR DRAINAGE STRUCTURE TYPE SELECTION
Based on the hydrological and hydraulic analyses of the catchments, contributing flow to the
crossing and the site configuration, the types and sizes of the drainage structures have been fixed.
The culverts are either reinforced concrete slab/box or reinforced Concrete pipe culverts of
different sizes .In addition to the culverts required for the streams and other well-defined water
outlets, culverts are provided to discharge the side drains where they cannot be discharged
through turn out ditches.to reduce siltation and facilitate clearing and maintenance of pipes, the
minimum pipe size adopted is 1.22m in diameter. When the inlet level is much higher than outlet
level, cascaded end walls with masonry apron is provided on the outlet side to reduce erosion.
The total width of the road including shoulders, fill height, fill slope and flow gradient is
considered to determine the length of barrels of all culverts.
3.2.3 PIPE CLASS
The class of pipes is adopted from ERA’s 2013 standard detail drawings with minor modification
made to the reinforcement details.
3.2.4 PIPE BEDDING
Selection of pipe bedding is made in accordance with ERA’s 2013 standard drawing, ERA’s
Drainage Design Manual and ERA’s Standard Specification requirements. Accordingly,
 Class “A” bedding type is recommended for culverts located on rock, shale or other hard
material sections.
 Class “B” bedding type is recommended when soft or other objectionable founding
material as encountered as per during our site investigation findings,
 Class “C” bedding type is recommended when firm and good foundation material is
found
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3.3 MATERIALS PROPERTIES

Structural materials considered for design and recommended for the construction of minor and
major culverts of the project are described as follows.
3.3.1 CONCRETE
The classes of concrete used for the different component of minor and major culverts are taken in
accordance to ERA’s 2002 Standard Technical specification requirement. The recommended
grades of concrete and specified strengths are given in the table below: -
Table 3-1 :- Classes of concrete used for minor and major culverts
Concrete fck (MPa)
Recommended uses
Grade (150mm cube)
C25/20 25 Box/ Slab Culverts
C35/20 35 Precast RC Pipes
C20/30 20 Plain concrete footing and lined drains
C15/20 15 Blinding for box /slab culverts
Class “A” bedding for pipes
Grade 1:4:8 Blinding for pipe culvert end walls
3.3.2 REINFORCEMENT
ERA’s 2013 Standard Technical Specification is considered while selected grades of

reinforcement bars to be used for design and construction of minor and major culverts.
Reinforcing bars considered for the design are stated as below,
Table 3-2 :- Classes of concrete used for minor and major culverts
Diameter of Min. yield Modulus of
Grade of
Reinforcement bar Strength, fy Elasticity, Es Recommend for
Steel
(mm) (MPa) (MPa)
Precast RC Pipe
Less than 10mm Grade 40 300 200000
Culvert
Greater than or
equal to 10mm
Grade 40 300 200000 Slab culvert
and less than
20mm
Greater than or
Grade 60 420 200000 Slab culvert
equal to 20mm
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Minimum concrete cover indicated in table 9-5 of ERA bridge design manual is considered for
the design except that the absolute minimum value is 35mm.
3.3.3 STONE MASONRY
According to ERA Standard Technical Specification - 2013, stone masonry is divided into three
classes. For this project implementation, it is recommended to use Class “B” masonry grades for
pipe culvert end structures, substructures of slab culvert and retaining walls.
3.3.4 GABIONS
As per the requirement of the contract agreement, gabion box are used as erosion protection
work for culverts located at mountainous terrain and erodible/weak foundation material. The
procurement of materials for gabions cages is recommended to comply with the requirement
stated in section 9102 and 9103 of ERA’s 2002 standard technical specifications.
All wires used in the fabrication of gabions shall be galvanized in accordance with the provisions
of section 9102(c) of ERA’s 2002 Standard Technical Specifications. The geo-textile filter fabric
which is to be used along with the gabions shall meet the requirements of section 9102(e) of the
same specification.
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4 DESIGN METHOD
Drainage structure shall be designed for specified limit states to achieve the objectives of
constructability, safety, and serviceability, with due regard to issues of inspect-ability, economy,
and aesthetics.
Equation 1 below is the basis of the LRFD methodology, and it shall be satisfied for all specified
force effects and combinations thereof. Each component and connection shall satisfy Equation 1
for each limit state.
 i i Qi   Rn = Rf
Where:
For loads for which a maximum value of i is appropriate:
i = D R I  0.95(ERA Bridge Design Manual Chapter two, article 2.2)
Table 4-3 Loads for which a minimum value of i is appropriate
Ductility, Redundancy, Importance,  = D * R

D R I *I
Strength 1 0.95 1 0.95
Service 1 1 N/A 1
Fatigue 1 1 N/A 1
i = 1  1.0 (ERA Bridge Design Manual Chapter two, article 2.3)
D R I
i = load modifier: a factor relating to ductility, redundancy, and

Operational importance
i = load factor: a statistically based multiplier applied to force effects
Qi = force effect
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 = resistance factor: a statistically based multiplier applied to nominal resistance
Rn = nominal resistance
D = a factor relating to ductility
R = a factor relating to redundancy
I = a factor relating to operational importance
Rf = factored resistance: Rn
Table 4-4 Resistance Factors
Strength Limit States  (Factor)
Flexure and Tension 0.90
Shear and Torsion 0.90
For Compression in anchorage zones 0.80
4.1 SUPERSTRUCTURE DESIGN

The superstructure shall be designed for applicable strength, service; extreme event and fatigue
limit states as defined by the load groups in the LRFD specifications.
4.2 SUBSTRUCTURE DESIGN

Foundation elements shall be designed for applicable strength; service and extreme event limit
states as defined by the load groups in the LRFD specifications.
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5 CULVERT DESIGN
5.1 CULVERT DESIGN STANDARDS
5.1.1 GENERAL
Minor culvert structure is reinforced concrete pipe culverts and Major culvert structures are
concrete box culvert and Slab Culvert. Basically, standardization of design has to be adopted for
minor drainage structures. The standard drawings used for this project are prepared based on the
standard drawings provided in ERASDD 2013. The length of the barrels of culverts shall be
enough to provide at least the full roadway formation width at the top plus the width
corresponding to the fill slope ratio. To facilitate inspection and carry out repairs the minimum
vent dimension of the culvert shall normally be 1220mm. ERA Standards is adopted where
applicable and supplemented with specific designs as necessary.
5.1.2 DEAD LOADS
Self-weight of the structural and non-structural components such as wearing surface and utilities
are considered in the design. In addition, vertical and horizontal earth pressure on culverts shall
be based on the principles of soil structure interaction and design pressures shall be calculated as
being the result of an equivalent fluid weight. The dead load factors used in the design are as per
ERA 2013 manual for each strength or service limit state considered.
5.1.3 LIVE LOADS
All culverts shall be designed to carry traffic live load of HL-93 (that includes HS20-44 or
Tandem and Lane Loading) by employing ERA’s Bridge Design Manual 2013. Live loads shall
be distributed through the earth cover as specified AASHTO LRFD Bridge Design Specification.
For Standard Reinforced Pipe Culvert Installations, the live load on the pipe shall be assumed to
have a uniform vertical distribution across the top of the pipe and the same distribution across the
bottom of the pipe.
The Critical loading effect of live loads used in the design by applying influence line diagrams
for different loading locations along the structure span.
5.1.4 DISTRIBUTION OF WHEEL LOADS THROUGH FILLS
The height of fill over reinforced concrete pipe and slab culverts before allowing any traffic
loading to pass shall be at least be 0.6m or more. Where the depth of fill is less than 0.6m, the
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effect of the fill on the distribution of live load shall be neglected. Live load distribution for
culvert tops may be based on provisions for deck slab spanning parallel to traffic. Where the
depth of fill exceeds 0.6m, wheel loads may be considered to be uniformly distributed over a
rectangular area with sides equal to the dimension of the tire contact area and increased by either
1.15 times the depth of fill in select granular backfill, or the depth of the fill in other cases.
Where such areas from several wheels overlap, the total load shall be uniformly distributed over
the area. For single span culverts, the effects of live load may be neglected where the depth of fill
is more than 2.4m and exceeds the span length; for multiple span culverts, live load effects may
be neglected where the depth of fill exceeds the distance between faces of end walls.
5.1.5 DESIGN METHODOLOGY OF CULVERTS
The methodology of design is the basic principle of structural engineering that the available
capacity of a structure must exceed the required capacity to support the applied loadings. The
methodology utilizes Load and Resistance Factor Design (LRFD) based on limit state as per
ERA’s bridge design manual 2013/ Latest AASHTO LRFD.
5.1.6 GENERAL DESIGN CRITERIA AND LOADINGS
The basic design criteria and loadings pertaining to the design of culverts have been summarized
in the table below:
Table 5-5:- Design criteria for Culverts
Criteria Value
Dead Loading Dead weight of the structure including the overlying material.
Live Loading Design vehicular live load as per ERA’s Bridge Design Manual
2013, HL-93 which comprises: design truck with design lane, and
design tandem with design lane.
Impact Factor Dynamic load allowance as per the Manual.
Exposure Condition Moderate
Railing/ Parapets For at grade culverts, concrete parapets shown in ERA’s Standard
Drawing will be used.
Abutment and Wing Cement-mortared stone masonry will be used for slab culvert
wall
Culvert width (At grade As per the cross section of the road
culverts)
Earth Pressure of Rankin’s theory, Equivalent fluid weight of fill material is taken as:
backfill -19KN/m3
-Live load surcharge pressure equivalent depends on the height of
substructure.
Material strength As per ERA’s Standard Technical Specification 2013.
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5.1.7 MATERIALS
Structural materials considered for design of minor drainage structures (Culverts) on the project
are reinforced concrete and stone masonry.
5.1.8 CONCRETE
The recommended grades of concrete and specified strengths are given below:
Table 5-6Classes of concrete used for culvert design

Minimum cube Minimum
Classes of (150mm) cylinder Applicable structural
concrete compressive compressive components
strength at 28 Strength at 28
days, fc’ [MPa] days, fc’ [MPa]
Class C35/20 35 28 Pipe

- Slab culvert superstructures
Class C30/20 30 24 - Box culvert, wing walls, apron slab,
and cutoff wall
Class C25/20 25 20
Slab culvert footings
Class C15/20 15 12 Lean concrete in blinding
Modulus of Elasticity of Concrete, Ec = 4800√fc’, for normal weight concrete
Design properties of concrete for other uses are as stated on ERA Bridge Design Manual - 2013
(Chapter-7: Reinforced Concrete)
5.1.9 REINFORCEMENT
Reinforcing bars shall be deformed except for spirals, hoops and wire fabric. The minimum
nominal yield strengths of deformed bars are as described in the table below,
Table 5-7: Grades of reinforcement steel for structure design

Diameter of bar,, Grade of Min. yield Modulus of Elasticity,
[mm] strength, fy [MPa] Es [MPa]
Steel
< 20mm Grade 300 300 200x103
≥ 20mm Grade 420 420 200x103
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5.1.10 STONE MASONRY
For implementation of this project, it is recommended using Class B masonry grades for culvert
end-walls and other protection works in compliance with the requirements of material properties
Stated in ERA’s Standard Technical Specifications 2013.
5.1.11 CULVERT SIZES SHAPE AND LAYOUT
The culvert size and shape selected is to be based on Hydraulic and economic criteria related to
site conditions. Absolute minimum sizes of 1220 millimeters for cross culverts are used to avoid
maintenance problems and clogging:
End walls or wing walls are used to retain the roadway embankment to avoid a projecting culvert
barrel. They are also used where the side slopes of the channel are unstable, and where the
culvert is skewed to the normal channel flow.
The selection of end structure for pipe culverts is generally dependent on factors such as the
condition of the approaching channel, slope and stability of the outlet channel. The culvert inlet
type is selected from standard details from the Standard drawing prepared by the consultant
based on ERA’s Standard Detail Drawings.
Aprons are used to reduce scour from high headwater depths or from approach velocity in the
channel. They should extend at least 2m at inlet and 3m at outlet side and should not protrude
above the normal streambed elevation. Outlet protection (dissipaters) for the selected culvert
design flood is provided where the outlet scour is anticipated:
 The Scour hole will undermine the culvert outlet,

 The expected scour hole may cause costly property damage,
 The Scour hole causes a nuisance effect (most common in urban areas)
5.1.12 MATERIAL SELECTION
Concrete and masonry are the preferred material for construction of culverts. In evaluating the
suitability of alternate materials, the selection process is based on a comparison of the total cost
of alternate materials over the design life of the structure that is dependent upon the following:
 Durability (service life),

 Cost
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 Availability
 Construction and maintenance ease
 Structural strength
 Traffic delays and
 Water tightness requirements.
5.2 PROPOSED TYPES OF CROSS DRAINAGE STRUCTURES

According to the final hydrology and hydraulic study result and detail site investigation findings,
a total of 100 pipe culverts, 24 box culverts and 1 bridge are recommended to be constructed.
The summary and the list of the proposed cross drainage structures are shown in the tables
below:
Table 5-8: Summary of Minor Structures

Type Dimensions (m) Number
Reinforced Concrete Pipes 1.22 100
Box Culvert All Sizes 24
Total Culvert along the 124
alignment
ERA’S Standard design drawings are adopted with relevant modifications for drainage structures
with a span of less than 6m. Where required, as recommended by the hydraulic study and
structure site condition, the required design is made as per ERA-Bridge-Design Manual-2013.
5.2.1 REINFORCED CONCRETE PIPE CULVERTS
Standard detail of prefabricated reinforced concrete pipes are adopted from ERA’s 2013
Standard detail drawings with minor review/modifications made to the original drawing so as to
avoid self-discrepancy between the details and descriptions. The standard detail for end walls of
pipe culverts are designed to be constructed from class “B” cement-mortared stone masonry as
per ERA’s 2013 Standard detail drawings provisions. Some modification is made to the standard
provision so that it can comply with the actual site condition and road way typical cross section.
Joints between the pipes shall be sealed with reinforced concrete capping to prevent infiltration
of water and fine soils. Depending on the foundation material three different types of pipe
bedding have been designed to provide uniform support for the entire length of pipe.to prevent
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scouring at the inlet and outlet level masonry paved water way and cut-off walls have been
provide.
The design list of pipe culverts for the station 170+600- station 242+300 is shown on the
following table. The detailed pipe culvert schedule is also attached in Appendix B.
Table 5-9: List of Proposed Pipe Culverts
OID Station Type Proposed Cross Drainage Structures Size
1 172+005 Pipe 1 1220
2 173+667 Pipe 1 1220
3 174+800 Pipe 1 1220
4 175+599 Pipe 2 1220
5 176+576 Pipe 1 1220
6 177+023 Pipe 1 1220
7 177+732 Pipe 1 1220
8 178+120 Pipe 1 1220
9 178+204 Pipe 1 1220
10 178+664 Pipe 1 1220
11 178+995 Pipe 1 1220
12 179+317 Pipe 1 1220
13 180+184 Pipe 1 1220
14 180+400 Pipe 1 1220
15 180+978 Pipe 1 1220
16 183+113 Pipe 1 1220
17 183+447 Pipe 1 1220
18 184+098 Pipe 1 1220
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19 184+555 Pipe 1 1220
20 184+722 Pipe 1 1220
21 184+804 Pipe 1 1220
22 184+954 Pipe 1 1220
23 185+088 Pipe 1 1220
24 185+388 Pipe 1 1220
25 185+637 Pipe 1 1220
26 185+897 Pipe 1 1220
27 186+200 Pipe 1 1220
28 186+701 Pipe 2 1220
29 186+955 Pipe 1 1220
30 187+499 Pipe 1 1220
31 188+163 Pipe 1 1220
32 188+699 Pipe 1 1220
33 189+590 Pipe 1 1220
34 189+738 Pipe 1 1220
35 190+191 Pipe 1 1220
36 190+326 Pipe 1 1220
37 190+475 Pipe 1 1220
38 190+707 Pipe 1 1220
39 191+282 Pipe 1 1220
40 191+453 Pipe 1 1220
41 191+653 Pipe 1 1220
42 191+751 Pipe 1 1220
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43 192+075 Pipe 1 1220
44 192+805 Pipe 1 1220
45 193+326 Pipe 1 1220
46 193+586 Pipe 1 1220
47 193+931 Pipe 1 1220
48 194+891 Pipe 1 1220
49 195+439 Pipe 1 1220
50 195+755 Pipe 1 1220
51 196+156 Pipe 1 1220
52 196+379 Pipe 1 1220
53 197+760 Pipe 1 1220
54 199+700 Pipe 2 1220
55 200+290 Pipe 1 1220
56 200+940 Pipe 1 1220
57 201+550 Pipe 1 1220
58 203+880 Pipe 1 1220
59 205+720 Pipe 2 1220
60 206+140 Pipe 1 1220
61 208+680 Pipe 2 1220
62 209+180 Pipe 1 1220
63 210+200 Pipe 1 1220
64 211+100 Pipe 1 1220
65 211+820 Pipe 1 1220
66 212+220 Pipe 1 1220
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67 212+625 Pipe 1 1220
68 214+400 Pipe 2 1220
69 214+720 Pipe 1 1220
70 216+945 Pipe 1 1220
71 217+100 Pipe 1 1220
72 219+533 Pipe 1 1220
73 219+956 Pipe 1 1220
74 220+920 Pipe 1 1220
75 221+980 Pipe 1 1220
76 223+960 Pipe 1 1220
77 226+480 Pipe 2 1220
78 226+708 Pipe 1 1220
79 227+100 Pipe 2 1220
80 227+960 Pipe 1 1220
81 228+415 Pipe 1 1220
82 228+795 Pipe 2 1220
83 233+483 Pipe 1 1220
84 234+140 Pipe 1 1220
85 234+660 Pipe 1 1220
86 235+000 Pipe 1 1220
87 235+880 Pipe 1 1220
88 236+736 Pipe 1 1220
89 237+430 Pipe 1 1220
90 237+735 Pipe 1 1220
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91 237+820 Pipe 1 1220
92 239+430 Pipe 2 1220
93 240+020 Pipe 1 1220
94 240+030 Pipe 1 1220
95 240+280 Pipe 1 1220
96 240+380 Pipe 1 1220
97 241+015 Pipe 1 1220
98 241+280 Pipe 1 1220
99 241+290 Pipe 1 1220
100 241+700 Pipe 2 1220
5.2.2 SELECTION BETWEEN SLAB AND BOX CULVERTS
According to the Final Hydrology/Hydraulics report of the section from station 170+000 –
242+300 there are 24 box culverts with spans and heights as shown in the table below have been
recommended.
Table 5-10: List of Proposed box Culverts
OID Station Type Proposed Cross Drainage Structures Size
No. cells Span (m) Height (m)
1 170+698 Box 1 3 2
2 170+975 Box 1 3 2
3 171+441 Box 1 4 3
4 171+626 Box 1 3 2
5 172+854 Box 2 4 4
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6 173+795 Box 1 3 3
7 176++355 Box 1 4 3
8 176+712 Box 2 4 4
9 182+585 Box 2 4 3
10 187+278 Box 1 3 2.5
11 187+741 Box 1 4 3
12 189+072 Box 2 4 3
13 190+019 Box 1 3 2
14 192+006 Box 1 3 3
15 192+420 Box 1 4 3
16 196+747 Box 1 3 3
17 213+500 Box 1 3 2.5
18 215+989 Box 1 4 3
19 222+630 Box 1 4 3
20 224++857 Box 2 4 3
21 231+300 Box 1 4 3
22 231+600 Box 2 4 3
23 232+138 Box 1 3 2
24 228+020 Box 2 6 3
5.2.2.1 FOUNDATION INVESTIGATION
The foundation conditions of each major culvert crossing sites will be carryout in the future and
structure type selection report will be submitted separately.
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5.3 COMPONENTS OF CULVERTS
5.3.1 HEADWALLS:
For prefabricated reinforced concrete pipe culverts, Class B stone masonry headwalls &
wing wall shall be provided. These retain and protect the embankment at the ends of the
culvert and help to counteract the dislocation of concrete pipes due to lateral earth fill
forces at base of embankment.
5.3.2 INLET AND OUTLET STRUCTURE:
The culverts’ inlet and outlet type and configuration has been selected based on
 Invert level of pipe (to determine type of end wall and inlet)
 The longitudinal ditch slope and level (type of inlet)
 Steepness of ground cross sectional slope (necessity of energy dissipater)
 Type of culvert (pipe or slab/box)
To prevent scouring at the inlet and outlet proper measures have been taken. For inlets paved
water way and cut-off walls have been provided. Whereas for outlets two cases of outlet
conditions are encountered during determination of type of structure. The first case is where
there is no significant elevation difference between the outlet level of the culvert and the
surrounding ground. In this case normal outlet paved waterway was provided. Moreover, the
outlet velocity was controlled by adopting mild slope for the culvert. The second case is where
there is marked difference between the outlet level of the pipe and the surrounding ground. In
this case energy dissipating structures including cascades, retaining walls in conjunction with
paved waterway have been used. Details of these structures, their respective locations and
measurements will be delivered on the working drawing stage.
5.3.3 APRONS AND CUT-OFF WALLS AT INLET AND OUTLET:
Aprons are provided to reduce scouring from high headwater depths or from approaching
velocity in the channel. They have extended 2m to the inlet and 3m to the outlet side and
should not protrude above the normal streambed level. Outlet protection (dissipaters) and
check dams for the selected culvert design flood is provided where the outlet scour is
anticipated.
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5.3.4 EROSION PROTECTION:
Scour control measures at culvert inlet and outlet shall be designed which includes, outlet
channeling & Stone pitching at the inlet and outlet with cut-off walls of each pipe culvert.
5.3.5 CULVERT SKEWNESS:
In accordance with the ERA DDM angle of skew limits, skew culvert shall be provided for
culverts with the reference of Centre line of the culvert and roadway profile.
The selection shall be based on:
 Proper catchment of the flow

 Standard requirement,
 Experience and appropriate engineering judgment.
5.3.6 CONSTRUCTION METHOD AND MATERIALS
The design consideration has assumed to make use of all available construction materials and
labor input. In this line, the structures are mainly to be constructed using reinforced concrete and
masonry. Accordingly, all super structural elements are to be of reinforced concrete, while the
substructures are to be made using stone masonry of class B, with or without Reinforced
concrete pad.
6 BRIDGE DESIGN
6.1 BRIDGE LOADING
Based on the reinforcement of the ERA bridge design Manual-2013, the following
permanent and transient loads and forces are considered in the design of highway
structures.
6.1.1 PERMANENT LOADS
6.1.1.1 Dead load of structural components and non - structural attachments (DC)
AS the structures are reinforced concrete, this load is dead load of concrete (Unit Weight
=24.5KN/m3
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6.1.1.2 Dead load of wearing surfaces and utilities (DW)
Bituminous Wearing surfaces have been assumed on deck surfaces as a wearing surface
(Unit Weight 225KN/m3) for future provisions.
6.1.1.3 Vertical pressure from dead load of earth pressure (EV)
Rolled Gravel or Hand Laid Rock Ballast as earth fill material is assumed (unit weight
taken is 19.5 KN/m3)
6.1.1.4 Horizontal Earth pressure Load (EH)
Lateral earth pressure is assumed for walls backfilled with earth. The walls are reviewed
and designed assuming that they can move from the soil mass. The coefficient of lateral
earth pressure will be determined from the permitted backfill materials.
6.1.2 TRANSIENT LOADS
AS per ERA BDM-2013, and ASHTO LRFD 2004 the design vehicle load for the design of new
bridges shall be HL-93. The new Vehicular load, HL-93, consists of “Design Truck” or “Design
Tandem” simultaneously loaded with a lane load. Whichever design loadings creating the
maximum effect have considered in the design of the bridges. Consideration should be given to
site-specific modifications to the design truck, design tandem, and/or the design lane load under
the following conditions:
The roadway is expected to carry unusually high percentages of truck traffic flow control, such
as a stop sign, traffic signal, or control both, causes trucks to collect on certain areas of a bridge
or to not be interrupted by light traffic or special industrial loads are common due to the location
of the bridge.
6.1.3 DYNAMIC LOAD ALLOWANCE
The static effects of the design truck or tandem, other than centrifugal and braking forces, shall
be increased for dynamic load allowance. The factor to be applied to the static load shall be taken
as (1+IM/100), where IM is the Dynamic load allowance.
6.1.4 SECONDARY LIVE LOADS
Load due to vehicle collision with bridge parapets have been taken from the AASHTO Standard
Highway Loadings for barriers.
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6.1.5 VEHICULAR LIVE LOADS (LL)
6.1.5.1 Design Truck Load
Total of design truck is 325KN distributed between 3 axles. Front axle loading is 35KN and two
rear axles loading is 145 KN each. Distance between front and first rear axle is 4.3m. The
distance between two rear axles varies from 4.3m to 9m to produce extreme
Force effects. These weights and spacing for axles are as specified in Figure 3-4 of ERA Bridge
Design Manual-2013.
Figure 6-6 Design Truck Load
6.1.5.2 Design Tandem Load
Design tandem load is exceptional loading and shall be applied for military vehicle loading and
for strategic bridges. Design tandem comprised of a pair of 110KN axles spaced at1.2m.Each
axle comprised of two wheels spaced at 1.8m transversely.
Figure 6-7 Design Tandem Load
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6.1.5.3 Design Lane Load
Design lane load consist of 9.3 KN/uniformly distributed longitudinally. Transversely, the load is
assumed to occupy a 3.0m width
6.1.6 PEDESTRIAN LOAD
A pedestrian load of 4KN/m2 is applied to all walkways wider than 0.6m. They are considered to
act simultaneously with the vehicular design live load.
6.1.7 ENVIRONMENTAL EFFECTS
Environmental effects are those resulting from natural effects such as wind, temperature and
seismic events.
6.1.7.1 Wind Load
It has been assumed that the base wind speed for structure (VB) is 145KM/h.
6.1.7.2 TEMPERATURE LOAD
A temperature range from 5 degree to 35 degree has been assumed in the design of critical
elements. For the calculation of effects due to temperature gradients through superstructures the
appropriate values are:
T1=35 degree, T2=10 degree, T3=5 degree
6.2 MATERIALS
The structural materials generally used for design of highway structures are reinforced concrete
and stone masonry
6.2.1 REINFORCED CONCRETE
Design of concrete materials is based on the properties given below.
6.2.1.1 Concrete
Adopted grade of concrete and corresponding specified strength are shown below
Grade of Concrete: -C30, Fck (150mmcubes) =30mpa at 28 days.
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: -C25, Fck (150mmcubes) =25mpa at 28 days.
: -C15, Fck (150mmcubes) =15mpa at 28 days.
Other design properties of concrete are used as stated on ERA bridge design Manual-2013
(chapter-9 reinforced concrete)
6.2.1.2 Reinforcement Steel
Reinforcing bars shall be deformed except for spiral, hoops and wire fabric. The minimum
nominal yield strength of deformed bars is as stated below,
AASHTO M31 M Grade 300:-300 Mpa
AASHTO M31 M Grade 420:-420 Mpa
6.2.1.3 Stone Masonry
According to ERA standard technical specification-2013, stone masonry is divided into three
classes. However, the consultant has used Class B stone masonry for the construction of major
watercourse crossing structures (Bridges) and minor watercourse crossing structures (culverts).
This grade of stone masonry shall conform to the requirement of ERA standard technical
specification-2013
6.3 MAJOR DRAINAGE STRUCTURES DESIGN
6.3.1 GENERAL
According to the hydrological and hydraulic analysis one bridge is required in this road project.
The bridge is located at station km 174+950.
Bridge Site Selection
Economical and safe bridge-crossing site has been selected for the bridge as far as site conditions
permit. In selecting the crossings, it has been targeted to achieve the following:
 Straight reach of the rivers.

 Well defined and stable banks.
 Short span feasible.
 Good foundation material.
 better horizontal and vertical alignments along the road
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 location beyond disturbing influence of tributaries
6.3.2 SPAN DETERMINATION
In addition to the hydraulically recommended spans, economic, safety, stability and ease and
time construction have been considered in the structural recommendations of the spans of the
bridge. The following table illustrates the type and span arrangement of the proposed bridge.
Table 6-11 Structural Recommendation of bridge @ 174+950
OID Station Proposed Cross Drainage Structure
Type Span/Dia.(m) Height (m) No. cells
1 174+950 Bridge 60 HWM=1310.9 1

8
6.3.3 SUPERSTRUCTURE DESIGN
The span of 40m superstructure has been designed for bridges. The superstructure is designed
using Load Factor Design Method. The proposed RCDG superstructure is composed of
reinforced concrete deck girders and 0.22m thick reinforced concrete deck.
In the design of the superstructure, the following loads are considered.
 Dead Load.
 Live Load HL-93 load Design Truck and Lane Loading, and Design Tandem and
Lane Loading
 Impact or dynamic effect of Live Load.
 Wind Loads.
 Longitudinal Forces and Horizontal Forces at Bearing Level etc.
Load combinations are also applied according to ERA BDM 2013. Accordingly, the design
Loads and resulting stresses (shear forces and bending moments) are calculated at different
section and the sections are designed to carry these loads and stresses. Finally, Dead Load and
Live Load deflections are checked for the allowable limits and camber is provided at mid span
for the calculated dead load deflection. The statical calculations for the design of the
superstructures are annexed in this draft Structure Design report.
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6.3.4 SUB STRUCTURE DESIGN
The substructures of the two bridges in the section of the project road are designed to be
composed of masonry abutments and wing walls and column bent piers. The following loads are
considered in the design of substructure of the subject bridges.
 Maximum reactions of dead and live loads of superstructures

 Substructure Dead Load.
 Wind load on structure
 Wind load on substructure
 Wind load on live loads
 Surcharge load,
 Braking load,
 Earth pressure loads
The substructures are designed as gravity retaining walls to resist overturning, sliding and
bearing failures due to their own weight and loads imposed on them.
The loads and the load combinations are applied in the Stability Analysis of the substructure. The
stability of the Abutments is checked against Overturning, Bearing Pressure and Sliding. The
statical calculations for the design of the substructures are annexed in this draft Structure design
report.
As the geotechnical investigations of the bridge sites are preliminary as described in the next
section, the substructure design may have to be revised on the bases of the detail geotechnical
investigation results.
6.4 GEOTECHNICAL INVESTIGATION
The foundation conditions for major crossing sites will be carryout and geotechnical
investigation report will be submitted separately.
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6.5 MISCELLANEOUS DESIGN
6.5.1 BRIDGE RAILING
Railings shall be provided along the edges of structures for protection of the traffic and
pedestrians. Reinforced concrete posts and railings are provided. The concrete used for the posts
and railings is class “Y”.
6.5.2 BRIDGE BEARINGS
Elastomeric Bearings have been provided to transmit loads from superstructure to the
substructure and accommodate movements between the bridge and its supporting structure.
6.5.3 DECK DRAINS
To avoid accumulation of rainwater on the bridge surface, deck drains are provided at quarter
points of the deck of the superstructure.
6.5.4 DECK JOINT SEALS
Where significant movements due to temperature variation is expected, joint seals are required to
prevent the intrusion of material and water through the joint system in addition to
accommodating these movements. The type of joint seal used here is a pre-molded expansion
joint filler type and is provided at the ends of the superstructure and approach slabs.
6.5.5 APPROACH SLABS
Approach slabs are required to provide a safe ramp on to the deck in case of settling of approach
embankment. Reinforced concrete approach slabs, at both ends of the bridge structures, have
been provided with a thickness of 0.3m and length not less than 5.0m.
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Appendix A
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Consultancy Service for Detailed Engineering Draft Structural Report

Design of Yabelo - Metagefersa- Shakiso

2.1 Criteria of Assessment and Inventory........................................................................8

2.2 Drainage Structures Inventory...................................................................................9

2.3 Minor Drainage Structures Inventory......................................................................10

2.3.1 Observed Damages on Minor Structures.........................................................10

2.3.2 Recommendations on existing Minor Structures.............................................12

2.4 Drainage Major structures Inventory.......................................................................12

2.4.1 Details of Bridge..............................................................................................12

2.4.2 Recommendation on Existing Major Structures..............................................13

2.5 Strength Evaluation of existing structure.................................................................13

3 STRUCTURES DESIGN STANDARED AND CRITERIA..........................................14

3.1 Structure Design Standards......................................................................................14

3.2 Structure Type Selection..........................................................................................14

3.2.1 Major Drainage Structure Type Selection........................................................14

3.2.2 Minor Drainage Structure Type Selection.......................................................14

3.2.3 Pipe Class.........................................................................................................15

3.2.4 Pipe Bedding....................................................................................................15

3.3 Materials properties..................................................................................................15

Walabu Construction Share Company as Contractor and

G and Y Engineering Consult plc. As a Design Partner. i

3.3.3 Stone Masonry.................................................................................................16

4.1 Superstructure Design..............................................................................................19

4.2 Substructure Design.................................................................................................19

5.1 Culvert Design Standards.........................................................................................20

5.1.2 Dead Loads.......................................................................................................20

5.1.3 Live Loads........................................................................................................20

5.1.4 Distribution of Wheel Loads through Fills......................................................21

5.1.5 Design Methodology of Culverts.....................................................................21

5.1.6 General Design Criteria and Loadings.............................................................21

5.1.10 Stone Masonry.................................................................................................23

5.1.11 Culvert Sizes Shape and Layout......................................................................23

5.1.12 Material Selection............................................................................................24

5.2 Proposed types of cross drainage structures.............................................................24

5.2.1 Reinforced Concrete Pipe Culverts..................................................................25

5.2.2 Selection Between Slab and Box Culverts.......................................................30

5.3 Components of Culverts...........................................................................................32

Walabu Construction Share Company as Contractor and

G and Y Engineering Consult plc. As a Design Partner. ii

5.3.2 Inlet and Outlet Structure:................................................................................32

5.3.3 Aprons and cut-off walls at inlet and outlet:....................................................33

5.3.4 Erosion Protection:...........................................................................................33

5.3.5 Culvert Skewness:............................................................................................33

5.3.6 Construction Method and Materials.................................................................33

6.1 Bridge Loading.........................................................................................................34

6.1.1 Permanent Loads..................................................................................................34

6.1.2 Transient Loads................................................................................................34

6.1.3 Dynamic Load Allowance................................................................................35

6.1.4 Secondary Live Loads......................................................................................35

6.1.5 Vehicular Live Loads (LL)..............................................................................35

6.1.6 Pedestrian Load................................................................................................36

6.1.7 Environmental Effects......................................................................................37

6.2.1 Reinforced Concrete.........................................................................................37

6.3 Major Drainage Structures Design...........................................................................38

6.3.2 Span Determination..........................................................................................39

6.3.3 Superstructure Design......................................................................................39

6.3.4 Sub structure Design........................................................................................40

6.4 Geotechnical Investigation.......................................................................................40