IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

ANALYSIS AND DESIGN OF VOIDED SLABBRIDGE

Noura Ismail Ahamed1, Ayona Nair S2

1
M.Tech (Structural Engineering), Department of Civil Engineering, MVJCE, Karnataka, India
2
Assistant Professor, Department of Civil Engineering, MVJCE, Karnataka, India

Abstract
Circular voids are often incorporated into concrete bridge decks to reduce their self-weight without greatly reducing their
flexural stiffness. Incorporating voids within the deck slab offers many advantages over a conventional solid concrete slab like
lower total cost of construction, reduced material use and increased structural efficiency. However the voids within the structure
complicate the analysis of the structure. In this thesis a manual analysis for both longitudinal and transverse direction of voided
slab bridge is done as per the industrial standards. For transverse analysis the bridge is idealized using STAAD pro software. The
detailing of the complicated structure is also included in order to understand how the reinforcement is placed in the structure.

Keywords — Voids, Longitudinal Analysis, Transverse Analysis, STAAD pro

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1. INTRODUCTION Materials for Void Formers

For spans greater than 15 m, the dead load of a solid slab Various types of void formers have been used, spirally
becomes more and in order to lighten the structure voids of wound sheet metal being an early form. The voids became
rectangular or circular cross sections are incorporated near full of water during construction which resulted in the
the neutral axis. If the depth and width of voids are less than overstressing of the deck. The use of expanded polystyrene
60% of the overall structural depth, their effect on stiffness overcomes the problem of water logging since the material
is small and the deck behaves effectively as a plate. Voided consists of series of small closed cells whose porosity is less
slab decks are usually constructed with cast in situ concrete when compared to the total volume. It also has an advantage
with permanent void formers or it can be precast prestressed of being readily cut using hot wire inbfactory or using hand
concrete box beams post tensioned transversely to ensure saw in site.
continuity in the transverse direction.

Fig. 1 Typical Voided Slab Bridge

If the voids are in excess of 60%,their behavior becomes

cellular .Incorporating voids in the deck increases the cost
due to the complexity involved in the reinforcement
designed to resist transverse bending. However, self weight Fig. 2Spirally wound metal sheet
and area to be prestressed is reduced without effecting the
second moment of area. Also shuttering costs are less when
compared to cast in situ T sections. If the designer wishes to
reduce the structural depth this can be adopted by providing
proper stays when the concrete is poured and to prevent
floatation.

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

when solar radiation and other effects cause a gain in heat

and reverse temperature differences which cause heat to be
lost from the top surface.

Positive and reverse temperature differences for design of

concrete bridge decks shall be assumed according to Fig. 10
(a) of IRC: 6-2014.

Reduction in Longitudinal Effect

According to IRC: 6-2014 Cl 205, reduction in the
longitudinal effect on bridges having more than two traffic
lanes due to the low probability that all lanes will not be
subjected to the characteristic loading simultaneously.

Live load Combination

The live load combination shall be as per Table 2 IRC: 6-
2014 based on the number of lanes and the carriageway
width.

For carriageway width of less than 13.1 m, the higher

among the two combinations is taken
i. 1 lane of 70R +1 lane of class A
Fig. 3 Expanded Polystyrene ii. 3 lanes of class A

Bridge Loading The maximum of the above two combination is taken for
final live load bending moment and shear force in
The following loads are to be considered in the design of a
longitudinal direction.
bridge superstructure
2. LITERATURE REVIEW
Dead Load andSuperimposed Dead Load
Nipa Chauhan et al (2016) [1]: A comparison between
For most of the bridges self weight is the dominant loading.
prestressed solid and voided slab is conducted. For this
purpose models with different span length but with same
Weight of footpath, kerb, crash barrier, hand rail, wearing
width are prepared using SAP 2000 software and for both
coat, permanent fittings like lamp posts and ducts are
type of decks the bending moment, shear forces are found
included under superimposed dead loads, which are in
out for different span length. From the results it is concluded
addition to the self weight of the structure.
that voided slabs are more convenient and efficient when
compared to solid slab for bridge design. A decrease in
Live Loads moments from solid to voided slabs is about 11%, 7% and
Bridge girders carry loads which roll over them from one 5.5% for 20 m, 30 m and 40 m spans.
end to other. The Indian Road Congress in its code of
practice for road bridges specifies different types of B.Vaignan, Dr S.R.K Prasad (2014) [2]: Here analysis of
vehicular loads to be considered by giving wheel loads. The voided deck slab and cellular deck slab using Midas civil
two IRC loading standards considered for the design are: software is done for various spans ranging from 7m to 15 m
i. 70R Wheeled loading 9for an interval of 0.2 m. A total of 82 models are analyzed
ii. Class A loading and their beam forces, reactions have been compared with
respect to span. A real model of voided slab is taken for
Impact Load study and is analyzed by changing the voids into circular
and rectangular. It is concluded that cellular deck slabs have
The impact load due to collision effect shall be taken by an lesser displacements so it can withstand more load than a
increment of live load as an impact factor expressed in terms voided slab.
of percentage of live load. Impact factors for different class
of loadings are specified in IRC: 6-2014. Rajan Sen et al (1994) [3]: Two quarter scale continuous
longitudinally and transversely post tensioned, two lane
Temperature Stresses voided slab bridge models one straight and the other curved
are tested to determine the response to service load by
Provisions shall be made for stresses or movements
symmetrical placement of AASHTO truck loading. The
resulting from variations in the temperature. Effect of
voided slab is idealized as an orthotropic plate and ANSYS
temperature difference within the superstructure shall be
is used to conduct the analysis. The results show that there is
derived from positive temperature difference which occurs
reasonable agreement for the straight model but not for the
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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

curved model. This suggests that the equivalent orthotropic (ii) To obtain the critical load positions that causes severe
plate parameters need to be modified for the curved distress in the structure.
structures. (iii)To get an overall idea of how the complicated bridge
structures are designed in the industry.
El-Behairy S.A et al (1989) [4]: The general deformational
behavior of reinforced concrete voided slabs under 4. PRELIMINARY DATA FOR ANALYSIS
symmetrical and unsymmetrical cases of loading is studied
in this paper. For this six reinforced concrete slab with 10 The voided slab bridge considered here is a RCC
voids are tested. The dimensions of the slab are 1.04 x1.80 cast in situ simply supported bridge of span 30 m.
m and thickness 12 cm. The slabs are tested under single  Carriageway width =12.1 m
concentrated load and eccentric loading also. It is concluded  Overall width = 13 m
that decreasing the void depth ratio zimproves the load  Width of crash barrier = 0.45 m
distribution across the voided slab. Also, the orthotropic  Thickness of wearing coat=75 mm
plate theory can be used for the analysis of circular voided  Cantilever portion of deck=1.5 m
slabs with the stiffness of the slab being defined  Thickness of cantilever deck slab=0.35 m
appropriately.  Depth of voided slab =2.1 m
 No of voids in the deck=4
3. OBJECTIVES  Length of solid section at both ends= 3 m
(i) To perform a manual analysis for different loading  Grade of concrete=M35
combinations as per IRC loading criteria.  Grade of steel =Fe 500

Fig. 4 Cross section details of voided slab

Fig. 5 Cross section details of end section

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

5. ANALYSIS OF VOIDED SLAB BRIDGE occupies different positionson the deck and the maximum
response can becalculated for each of the loading case.
The analysis is done separately for both longitudinal and Since it willbe tedious to manually calculate the response
transverse direction. atevery 0.1 m, computer analysis program such asSTAAD
can be used.
5.1 Longitudinal Analysis
In longitudinal analysis, the bending moment and shear To analyze the effect due to live loads, first unitload is run
force due to dead load and live load are found in the to obtain the influence ordinates. Then ateach position of
longitudinal direction. The effect due to impact, temperature loading and combination, effectivewidth and equivalent
stresses are also included and also a reduction is done in the concentrated load per metrerun is calculated. Effective
longitudinal effect as all the lanes will not be subjected to width for each locationof load is calculated and thus each
characteristic loading. wheel load isconverted to wheel load per unit width of the
slab.
5.2 Transverse Analysis
For transverse analysis of the mid section, the deckis
Different load positions for each type of loading arechecked idealized as 13 beam elements connected withnodes at the
and the maximum response has to be foundout. For this the ends.
wheel load of the vehicle is movedtransversely such that it

Fig.6 Idealized bridge deck for transverseanalysis

Transverse analysis is carried out for the two

casesseparately
i. When the wheel is in the simply supportedportion
ii. When the wheel is in cantilever portion

5.2.1 Transverse Analysis of Simply

SupportedPortion
In order to find the locations ofmaximum bending moment
along thetransverse direction, the deck is idealizedinto beam
elements. The deck is modeled using STAAD software and
a unit load isrun and the influence ordinates are obtained.For
example for beam 4 the influenceordinate at every 0.1 m is
obtained fromSTAAD as shown in the figure below.

Now at each location effective width iscalculated for four

combinations i.e., 1 laneA, 2 lane A, 3lane A and 1 laneA+1
lane 70R wheeled and the maximum value isselected.

According to IRC 21:2000 Pg 52, effectivewidth for a solid

slab spanning in onedirection for a single concentrated load
isgiven by

beff= α a[1-a/lo]+bt, where

lo is the effective span

a is the centre of gravity of the concentrated loadfrom the
nearer support.
bt is the breadth of tyre+ twice the thickness ofwearing coat.
α is a coefficient depending upon the value b/lo ,where b is
the width of the slab.

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

Fig. 7 Beam end forces for beam 4 from STAAD

Fig. 9 Wheel `position for maximum positivebending

moment for beam 4

Now this concentrated load is applied on the modeland is

analyzed to get the moments at each section.This procedure
is repeated for all the other beamsand the moments are
obtained at each section.
Fig. 8 Influence line diagram for moment beam 4node 4
Thus, for various positions of loading the maximummoment
The effective width at the position of maximumbending from the different combination aresummarized as shown
moment is calculated. Then load pereffective width is found below.
and it is checked whetherthe loads will overlap and if so the
load is modified.

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

Table 1:Transverse Moment Summary

5.2.2 Transverse Analysis of Cantilever Portion 6. DESIGN OF VOIDED SLAB BRIDGE

Thecantilever portion of the voided slab bridge consistsof 6.1 Longitudinal Moments
the crash barrier and wearing coat.
The reinforcement details for the longitudinalmoments at
The dead load on the cantilever portion includes theweight midspan, l/3 and at a distance„d‟from the face of support are
from crash barrier, wearing coat and the selfweight of the summarized asshown below.
slab. For live load cantilever portionhas to be checked
individually for 70R loading andclass A loading.

Minimum clearance required in the case of 70Rloading is

greater than the length of the cantilever.Hence no live load
will be acting in 70R loading.Thus live load due to classA
loading is considered.The impact load is also added to get
the final liveload bending moment.

Table 2:Summary of Transverse Moments of Cantilever

Portion

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

Table 3:Area of Steel in Longitudinal Direction

Minimum steel in longitudinal direction at solidportion as 500mm2 /m or 0.35% of minimumflange area. The
per clause 305.19 of RC: 21-2000, reinforcement details in thetransverse direction are
= 0.15% of total cross sectional area=1650 mm2So provide summarized below. Crossreinforcement of 12 dia bars at
16 mm dia bar at 120 mm c/c. 150 mm c/c areprovided in order to keep the voids intact.

6.2 Transverse Moments Table 4:Area of Steel in Transverse Direction

As per clause 5.2.2.of IRC: SP: 64-2005,

Area of steel reinforcement

where he= c/c distance of compression and

tension flange, d=diameter of voids

Minimum transverse reinforcement in the bottom,as per

clause 8 of IRC: SP: 64-2005, In top andbottom of bottom
flange is 750mm2 /m or 0.5% ofminimum flange area.

Minimum transverse reinforcement in the top, asper clause 8

of IRC: SP: 64-2005, In top and bottomof top flange is
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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

7. DETAILING

Fig.10 Plan of the bridge

Fig.11 Detailing of Section A-A of the bridge

Fig.12 Detailing of Section 1-1

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IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308

Fig.13 Detailing of Section 2-2

8. CONCLUSION PostTensioned Voided Slab Bridge”, Journal of

StructuralEngineering ASCE, 1994.
The conclusions arrived after the analysis anddesign of the [4] El-Behairy S.A, Fouad N.A , Soliman M.I
voided slab bridge can be summarizedas follows: (1989),“Behaviour and Analysis of Voided concrete
 The design of the bridge superstructure is awork that slabs”,1989.
requires great expertise and alsoknowledge to foresee [5] Damien L Keogh, Eugine O Brien, “Bridge
unexpected situationsthat may come during the DeckAnalysis”, 1999.
constructionstage. [6] E C Hambly, “Bridge Deck Behaviour”,
 The longitudinal moments are the governingmoments SecondEdition, 1991.
and if the main bending has tosuffice it should not fail [7] S Ponnuswamy, “Bridge Engineering”,
in transversedirection. Secondedition, 2015.
 Transverse analysis makes the wholestructure as a [8] S SBhavikatti, “Structural Analysis- Volume
single unit thereby taking careof the stresses due to 1”,Fourth Edition, 2010.
individual loadings. [9] Indian Standard Codes
 Detailed analysis for the various IRCloadings have  Standard Specifications and Code of Practice
helped in understanding thecritical load position and forRoad Bridges, Section: ⅡLoads and Stresses-
combinations thatgovern the entire design. IRC:6-2014.
 If the void ratio is less than 40 %, the voidedslab can be  Standard Specifications and Code of Practice
analyzed using the same methodas that of solid slab in forRoad Bridges, Section: ⅢCement Concrete-
longitudinal direction. IRC:21-2000.
 Guidelines for the Analysis and design of Cast
ACKNOWLEDGEMENT inplace Voided Slab Superstructure-IRC: SP: 64-
The authors sincerely thank The Principal, Dr.Gunasekaran 2005.
N, the Head of the department,Prof. RavikanthTalluri,
Department of CivilEngineering, MVJCE, Bangalore for
theirguidance and support in completion of theproject.

REFERENCES
[1] Nipa Chauhan, Prof .Farhan A Vahora,“Comparative
Study and Design of PrestressedConcrete Solid and
Voided Slab Bridges”,International Journal for
Technological Research inEngineering, Volume 4,
Issue 2, 2016.
[2] B.Vaignan, Dr S.R.K Prasad, “Analysis of
Voideddeck slab and Cellular deck slab using
MIDASCivil”, International Journal of Engineering
Researchand Technology, Vol-3, Issue 9, September
2014.
[3] Rajan Sen, Mohsen Issa, X Sun, Antoine
Gergess,“Finite Element Modelling of Continuous

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