IRJET- Study of Static Analysis on Conventional and Oblique Prestressed Concrete Bridge Superstructure

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 06 | June 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 2830
STUDY OF STATIC ANALYSIS ON CONVENTIONAL AND OBLIQUE
PRESTRESSED CONCRETE BRIDGE SUPERSTRUCTURE
Thazneema CN1, Soumya Anand2
1M.Tech student, Structural Engineering & Construction Management, Amaljyothi College of Engineering, Kerala
2Assisstant Professor, Dept. of Civil Engineering, Amaljyothi College of Engineering, Kerala
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Abstract - Today the bridge construction has a worldwide
level of importance. Bridges are the key elements in any road
network, and use of prestress girder type bridges are most
popular in bridge engineering zone why because of its better
stability, serviceability, economy, aesthetic appearance and
structural efficiency. Theuseofprestressedconcretepavement
has some greater advantages and that can reduce slab
thickness, eliminate transverse joints and enhance durability
compared to traditional concrete pavement. Conventional
prestressing or precast prestressing in the longitudinal
direction requires additional space for anchorage and adds
more joints. This study proposes an oblique prestress concrete
bridge superstructure, in which prestressed tendons were
distributed with an angle (450) to the road direction so that
the prestress can be applied in the transverse direction. Also
compare the two methods of application of prestressing with
the help of software CSi Bridge. Analysis of sections was also
conducted. Oblique prestressing with 1m and 2m spacing is
modeled and analyzed for the purpose of study the effects of
increment in spacing.
Key Words: Conventional Prestressing, Oblique prestress,
tendons, transverse joints, CSi Bridge,
1. INTRODUCTION
Prestressed concrete combines high strength concrete with
high strength steel in an “active” manner. This can be
achieved by tensioning the steel and holding it against the
concrete, thus puttingconcreteintocompressionandisdone
to improve the performance of the concrete in service. The
most widely used prestressing approach is post-tensioning
in the longitudinal direction in the early stage. This
technique requires some space for the anchorage area atthe
two ends of the sections. In the oblique prestressingorcross
tensioned method, the prestressed tendons are distributed
obliquely with an angle in the road direction so that the
prestressing can be applied in transverse direction. By
adjusting the angle, the proportion of prestressing in the
transverse direction can be changed. The prestressinginthe
transverse direction provides lateral constraints to the slab
so that the transverse joints can be eliminated. The
anchorage area is on the side of the concrete slabs so that
long concrete slabs can be achieved without sacrificing the
prestressing. Finally the oblique prestressing on concrete
slabs can be used in achieving long span bridges without
providing prestressing on girders. [9]
1.1 Objectives
 To design the proposed bridge superstructure
including conventional prestressing
 Modeling the conventional and oblique prestressed
concrete bridge superstructure and analyze using
CSi Bridge software
 To study the effects of increasing tendon spacing in
oblique prestressing
 To compare the result of static analysis of 2 typesof
prestressing
1.2 Scope
This project is limited on designing and analyzing a
prestressed concrete bridge and the deck slab including
approach roads with the use of IRC code. And it doesn’t
cover hydraulic design and geotechnical design.
2. LITERATURE STUDY
Ling Yu et.al proposes an oblique prestressed concrete
pavement design criteria. Prestressed concrete pavement
can reduce slab thickness, eliminate transverse joints and
enhance durability compared to traditional concrete
pavement. Traditional prestressing or precast prestressing
in the longitudinal direction requires additional space for
anchorage and adds more joints. This study proposed an
oblique prestress concrete pavement, in which prestressed
tendons were distributed with an angle to theroaddirection
so that the prestress can be applied in both the transverse
and longitudinal directions. The detailed design of the
oblique prestress concretepavement,includingtheselection
of raw materials, design of cement concrete,anchoragearea,
size and distribution of prestressed tendons, stress analysis
within the concrete slab, sliding layer, side reinforcement,
and regular reinforcement at topandbottomareall included
in this study. The slab thickness, diameter, distribution
angle, and spacing of tendons were obtained based on the
stress analysis to meet the requirement of fracture criteria
and fatigue criteria. How the oblique prestressing is to be
provided in deck slab are as shown in figure 2.3. In addition,
the transverse prestress is beneficial to resist the traffic
related slab deformation, the tendon distribution angle is

varies from 25° to 45°. In terms of the spacing, tentative
values were used are: 0.5 m, 0.8 m, and 1.0 m.
Advantages of prestressing are, High-strength concrete and
high-tensile steel, besides being economical, make for
slender sections, which are aesthetically superior.
Prestressed concrete bridges can be designed as class I type
structures without any tensile stresses under service loads,
thus resulting in a crack-free structure. Prestressed
concrete is ideally suited for composite bridge construction
in which precast prestressed girders support the cast in
situ slab deck. This type of construction is very popular
since it involves minimum disruption of traffic. Post-
tensioned prestressed concrete finds extensive applications
in long-span continuous girder bridges of variable cross-
section. Not only does it make for sleek. Structures, but it
also effects considerable saving in the overall cost of
construction. [1]
3. METHODOLOGY
For the purpose of study an established details of a new
bridges at Kozhancherry area are to be selected.
Kozhencherry is a census town in Pathanamthitta
district of Central Travancore region (South Central Kerala)
in Kerala state, South India. It isonthebanksofriverPampa.
As per the part of eliminating the traffic congestion in
Kozhencherry bridge a new bridge layout has to be
proposed. As per the new proposed bridge, that has 207.2
meters long and 7.5 meterswideand1.125m widewalkway.
The bridge is made up of five spans in length 32 meters and
two 23.6 meters long end spans. 600mm wide kerbs are to
be provided on each side. Thickness of wearing coat is
80mm. IRC Class AA tracked vehicle loading is to be
considered for the design. For deck slab and prestressed
girders adopt, M45 grade concrete forconstruction.Analysis
of the bridge sections were done with the use of CSi Bridge
software. Again the oblique prestressing is applied to the
same model and also reduces the bridge section dimension.
Then analyze the model and ensurethatthesectionprovided
was satisfied or not.
Table –1: Dimensions of conventionally prestressed
concrete bridge superstructure
Bridge components Description Dimensions(mm)
Deck slab Thickness 200
Girder
Flange 500 x 400
Web 1320 x 200
As part of the study firstly, the conventionally prestressed
bridge superstructure were modeled and then analyzed.
Conventional prestressing means that prestressing tendons
were placed in longitudinal direction and follows the
parabolic path. And the superstructure consists of 4 girders
(2 internal and 2 external) to support thedeck slab.Thelight
green portion in the below figures indicatestheprestressing
tendon profiles.
Fig -1: Front view model of conventional prestressed
bridge superstructure
Table –2: Properties of materials used
Material Grade Poisson’s ratio Density (N/mm2)
Concrete M-45 33.5 x 103 2.4 x 10-6
Steel M-45 2 x 105 7.85 x 10-6
Table- 3: Mechanical properties of prestressing strands
Dimensions 15.2 mm dia. 7- ply high tensile strands
Class I type
Area (Ap) 139.4 mm2
Weight 1.094 kg/m
Ultimate tensile
strength (fp)
1723 N/mm2

3.1 Boundary Conditions
Displacement boundary conditions are needed to constrain
the model to get a unique solution. To ensure that the model
acts as the same way as the experimental bridge, boundary
conditions needed to be applied at points of symmetry and
where the supports and loading exist. In traditional
construction, the bearings are typically the controlling
feature of a seismic design and the piers or abutments are
assumed to be fixed.
3.2 Loading and Analysis
Live load is taken as IRC class AA tracked type loading.
According to IRC Class AA tracked loading the total load is
700 kN. In CSi Bridge software there is an option for
programme defined vehicular classes of different codes.
Vehicles are used to define the moving loads in CSiBridge
and are most often defined to act on the traffic lanes. There
are standard types of vehicles in the program, or users can
design unique vehicles using the general vehicle
specification. Vehicle classes are sets of oneormorevehicles
that can be assigned to act on lanes in a moving-load case.
Railing load are distributed as point loads on the left and
right edges. Load due to wearing coat are distributedasarea
load over the entire deck slab section. The definition of
moving vehicular load is shown in the figure below. And the
critical combinations of loads are (1.5dead load + 2.5 live
loads).
3.3 Modeling of Oblique prestressed bridge super
structure
In the normal prestressing the prestressing tendons are
provided in the longitudinal direction while in oblique
prestressing the tendons were provided obliquely with an
angle in the direction of road. As name indicates thetendons
are distributed in the deck slab of the bridge. In this type of
tendon profile pattern numerous numbers of strands were
placed, that behaves like a mesh. As part of the study the 2
models were created and analyzed. First model consist of
tendons with 1m spacing and second model consists of
tendons with 2m spacing. According to literatures the
tendon spacing varies from 0.5m to 1m. And the tendon
distribution angle from 25° to 45°.But for studying the
effects of increment in spacing the model with 2m spacing
and 450 distribution angle is created. In this model, the 2
interior girders were eliminated and theslabthicknesswere
reduced, that is only 150mm thickness of slab is provided.
And then analysis was done. Straight tendon profile is
followed in this model. And Material properties and
mechanical properties are same as in normal prestressing.
The elimination of girder and reduction in slab thickness is
done with respect to the literatures available. Finally check
the section provided is safe or not.
Fig -2: Plan of oblique tendons in each span
Fig -3: Front view of oblique prestressed bridge
superstructure
3.3.1 Varification of Section Provided in Oblique
Prestressing
Fig -4: Cross section of main girder
A = (2500 x 150) + (200 x 1320) + (400 x 500)
= 83.9 x 104 mm2
yt =
= 686.48 mm
yb = 1870-686.48 = 1183.52 mm
h1= 686.48 - ; h2 = 686.48 – 810= -123.52
mm and h3 = 686.48– 1670 = -983.52 mm
Ixx1 =

Ixx2 =
Ixx3 =
I = + +
= 2.504 1011 mm4
Zt = = 364.759 x 106 mm3
Zb = = 211.57 x 106 mm3
Results taken from software;
Mg = 3170.0842 kNm and Mq = 1144.2184 kNm
η = 0.85
fbr = 17 N/mm2
Zb (required) ;
= 95.27 x 106 mm3 < 211.57 x 106 mm3
Zb (required) < Zb (provided)
Hence the section provided is safe for the design.
4. RESULT AND DISCUSSION
Static analysis was carried out for the conventional
prestressed and obliquely prestressed concrete bridge
superstructure with 1 meter and 2 meter spacing.
Displacement, shear and moment values were obtained for
the respective bridges for comparison.
4.1 Conventional prestressed bridge
4.1.1 Maximum shear
Fig- 5: Bridge response plot for maximum shear value
4.1.2 Maximum moment
Fig-6: Bridge response plot for maximum moment
4.1.3 Maximum displacement
Fig-7: Bridge response plot for maximum displacement
4.2 Oblique prestressed bridge with 1m spacing
4.2.1 Maximum shear
Fig -8: Bridge response plot for maximum shear value
Fig -9: Bridge response plot for maximum moment value

Fig -10: Bridge response plot for maximum displacement
4.3 Oblique prestressed bridge with 2m spacing
4.3.1 Maximum shear
Fig -11: Bridge response plot for maximum shear value
Fig -12: Bridge response plot for maximum moment value
Fig -13: Bridge response plot for maximum displacement
Table -4: Comparison of results
Parameter Conventional
prestressing
Oblique with
1m spacing
Oblique with
2m spacing
Shear force
(kN)
1029.6846 836.7898 1012.671
Moment
(kNm)
6914.9616 5065.9544 5553.0544
Displacement
(m)
1.97 x 10-4 1.174 x 10-4 1.444 x 10-4
From the above data, the total shear force and bending
moment forconventional prestressingare1029.6846kN and
6914.9616 kNm respectively. While in oblique prestressing
the shear and bending moment will reduces. In oblique
prestressing with 1metre spacing the shear and momentare
836.7898 kN and 5065.9544 kNmrespectively.Therewill be
a greater reduction in shear and bending moment value
while comparing with conventional prestressing. This effect
is due to improved stiffnessinthetransversearrangementof
tendons in oblique prestressing. In oblique prestressing the
dead weight imparted by prestressing tendons will increase
than from conventional prestressing. But the dead weight
due to concrete sections such as, slab and interior girders
will reduce. Why because the 200mm thick slab will be
reduced into 150mm thick slab and 4 numbers of girders
will be reduced into 2 numbers of interior girders. There is
another advantage in case of oblique prestressingisthat,the
total cost of the structure can also be reduces. Why because
while providing oblique prestressing the number of girders
can be eliminated and also the slab thicknesswill bereduced
in a great extent. So that the cost of construction will
decreases as compared to conventional prestressing.
In addition, the transverse prestressisbeneficial toresistthe
traffic related slab deformation. In oblique prestressing the
anchorage to prestressing tendons were provided on
transverse direction that is on the either sides of the slabs
where as in conventional prestressing that was provided in
the longitudinal direction at each segmented sections. So
that in normal prestressing the space in between each
segmental sectionprovided will behigherwhy becausethere
should be enough space for anchorage. That will increases
the prestressing loss in case of long span bridges and also it
limits the length of the bridge section. In oblique
prestressing only conventional expanded joints were
provided in order to reduce the deformation of slabs. In
oblique prestressing the anchorage to tendons were
imparted through the sideways of the slab sectionand not in
longitudinal direction. And also the mesh arrangement will
obtained and this improves the strength and reduces the
moment in a great extent. Also that will reduce the depth of
the slab; it will also decrease the total dead weight.
According to Indian standards, the allowable deflection in
bridge structure should not be greaterthan (Span/1000).So
the allowable deflection is to be, (32/1000 = 0.032m). Here

the maximum deflection is 1.97x10-4m.Hencethedeflection
is within the allowable limit. The displacement in
conventional prestressed bridge is 1.97 x 10-4 m. And in
oblique prestressing with 1meter spacing is 1.17 x 10-4m. In
oblique with 2 meter spacing the displacement is 1.44 x 10-4
m. From these results, the displacement value of the oblique
prestressing will be lesser as compared to conventional
prestressing. The oblique prestressing with 2 meter spacing
shows slightly higher displacement than from oblique
prestressing with 1meter spacing. Hence the spacing of
tendons in oblique prestressing beyond 1meter increases
not only the shear force and bending moment but also the
displacement. But it never cross the displacement due to
conventional prestressing.
According to literatures, the tendondistributionanglevaries
from 250 to 450. The tendon distributionanglegreatlyaffects
the ratio of longitudinal stress and transverse stress. A
higher tendon distribution angle is expected to bring higher
longitudinal stress and lower transverse stress. Typically, a
higher longitudinal stress is desirable because it demands a
smaller tendon distribution angle. A low tendondistribution
angle would be more challenging to designandconstruct the
anchorage area. So thatdistributionangleof450 waschooses
for the modeling. From literatures, an increaseinspacefrom
0.5 m to 1.0 m would result in lower longitudinal and
transverse stresses. For study the effect what will occur
when the spacing is increased beyond 1m a parallel study
was conducted, so the oblique with 2m is taken into
consideration. And from the results, the oblique with 2m
spacing posses larger shear and moment as compared to
oblique with 1m spacing. Finally concluded that, when the
spacing increases beyond 1m the effects will have reverse
effect, that means the moment and shear force will gradually
increases. In terms of the effect of tendon spacing on the
stress level in the concrete slab, it can be realized that an
increase in space from 1.0 m to 2.0 m would result in higher
longitudinal and transverse stresses. This is paralleled with
expectation since a larger spacing (from 0.5m to 1m) results
in a lower reinforcement rate and therefore, lower load on
the concrete slab and the spacing from 1.0 m to 2.0 m the
loads become higher.
4. CONCLUSIONS
In this project, the static analysis of the conventional
prestressed, oblique prestressed with 1m spacing and
oblique prestressed with 2 m spacing were modeled and
analyzed. The static analysis was carried out to find the
shear force, moment and displacement of thecorresponding
structure. The structural modeling and analysis was done
using the software CSi Bridge. Only the superstructure
contains deck slab and girders were modeled. For the
supports of structure simply provided the abutments as
fixed supports. In this work the comparison of static
performance of the above mentioned 3 type bridge
superstructure were taken. The resultoftheanalysisreveals
that the oblique prestressed bridge performs well during
their life period as compared to the other two. Thefollowing
major conclusions were drawn based on the studies carried
out under this study;
* In conventional prestressing, the prestressing tendons
were provided in longitudinal direction. Most probably the
tendons were placed along girders. In case of long span
bridges, the prestressing will be done by using end blocks
and anchorage were provided on the ends of each segment.
So large space will needed in between each segments. This
will increases the prestress loss and also it limits the length
of the bridge section.
* While in oblique prestressing the tendons were
provided in transverse direction. Oblique prestressing can
be provided only along the slab section. In this case the end
blocks are located at certain intervals on either side of the
slab section. So the spacing in between segments can
eliminate.
* In oblique prestressing the prestressing tendons were
placed at an angle along the road direction at certain
intervals. A mesh like arrangement of tendons were
obtained, that will impart high pretension force through the
slab section
* Through oblique prestressing the depth of slab can be
reduced. And also it eliminates the requirement of large
number of interior girders. The design bending moment
value from the analyzed model is taken, and the section
provided is checked which is safe or not.
* The shear force and bending moment value of oblique
prestressing is decreased in a greater extent (around 18 %)
as compared to the conventional prestressing
* When the spacing of prestressing tendons in oblique
prestressing increased beyond 1.0 meter, the moment and
shear value will shows a declining effect.
* A low tendon distribution angle would be more
challenging to design and construct the anchorage area. So
that distribution angle of 450 provides the better result.
* The displacement value of the oblique prestressing will
be lesser as compared to conventional prestressing.
* The oblique prestressing with 2 meter spacing shows
slightly higher displacement than from oblique prestressing
with 1meter spacing. Hence the spacing of tendons in
oblique prestressing beyond 1meter increases not only the
shear force and bending moment but also the displacement.
But it never crosses the displacement due to conventional
prestressing.
* Hence finally concluded that, the oblique prestressing
with 1.0 m tendon spacing has better prestressing effects as
compared with conventional prestressing.
REFERENCES
[1] Amer F. Izzet, Ali A. Abdul hameed “Prestressed
Concrete: A Fundamental Approach, ACI 318‐11 Code
Philosophy & Stresses Limitations” published on
Research gate, April 2017

[2] Cleo Batocail, Julie Mae Clarabal, Glennie Lumampao,
Jethrine Claire Madarang and Edgardo Vargas Jr.(2013)
“Analysis and Design of a Prestressed Concrete Bridge”
Department of Civil Engineering Central Mindanao
University
[3] https://www.researchgate.net/publication/316494450
[4] “Introduction to CSiBridge” ISO BRG102816M1, United
States of America October 2016
[5] IRC 6-2016 “Standardspecificationsandcodeof practice
for road bridges” (seventh revision) December 2016
[6] IRC 18-2000 “Design criteria for prestressed concrete
road bridges- post tensioned concrete” (Third revision)
October 2000
[7] IRC 21-2000 “ Standard specifications and code of
practice for road bridges- section III –Cement concrete
(plain and reinforced)” (Third revision) October 2000
[8] IRC: SP-71-2006 “Guidelines fordesignandconstruction
of precast pre-tensioned girders for bridges” May 2006
[9] Ling Yu , Xu Yang, Xiaohui Yan, Xiaowei Zhang, Ting
Zhao, Cong Duan and Julian Mills-Beale (2018) “Design
And Construction f Oblique Prestressed concrete
Pavement: A Case Study In China” Journal of Applied
Science, 8, 607
[10] Lecture notes on “Prestressed Concrete Structures” by
Dr. Amlan K Sengupta and Prof. Devdas Menon, Indian
Institute of Technology Madras
[11] N. Krishna Raju, “Design of bridges”, fourth edition,
Oxford and IBH publishing Co. Pvt .Ltd. New delhi, 2010
[12] N.krishna Raju, “prestressed concrete bridges”, CBS
Publishers and distributors Pvt Ltd, 2012.

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