Parametric Study on Curved Bridges Subjected to Seismic Loading

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1883
Parametric Study on Curved Bridges Subjected to Seismic Loading
Anurag Deshpande1, H M Jagadisha2, Aravind Galagali3
1Mtech student, Manipal Institute of Technology, Karnataka, India
2Assistant Professor, Dept of Civil Engineering, Manipal Institute of Technology, Karnataka, India
3Professor, Dept. of Civil Engineering, BVBCET( KLE Technological University), Karnataka, India
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Abstract - As India is developing, the infrastructure is
gaining a lot of importance. This project aims at
infrastructure development such as bridges. The curvature
in the bridges is usually introduced to eliminate the support
irregularities or presence of important structures which
cannot be demolished. Due to the curvature in the bridge
there will be large centrifugal reactions on the vehicles.
Apart from the reaction a large torsional moment will be
induced on the supporting girders. The column’s location
and orientation is also a major design criteria in bridges.
When the columns are tilted from the normal angle the
column is said to be skewed. Skewed column decreases the
stability of structures as seen in the previous literatures.
Skewed columns along with some degree of horizontal
curvature to the bridges create a lot of instability. In this
project bridges subjected to seismic loads and its behavior
when the bridge is curved horizontally at deck section and
skewed at column or pier section is dealt.
The bridge model considered for the project
consisted of 2 spans each of 50m, with abutments at both
ends and piers at mid section. 2 columns of 1.5m diameter
were considered at mid section. In this project Box girder
bridge and I girder bridge are compared with horizontal
curvature being (R= inf, 150m, 250m) and columnskewness
with (0, 15, 25 degrees) variation. The results of the study
such as modal results and pushover results were tabulated
and compared with other bridge models. The software used
for the study is CSI Bridge 2016 v18 subjected to seismic
load subjected to code of 1893 2002 and IRC 6 for vehicle
loading.
Key Words: Box girder Bridge, I girder Bridge, Radius of
Curvature, Column Skewness
1. INTRODUCTION
From past few decades the infrastructurehasseena
great boom in the world. To access any inaccessible areas
bridges were built. Hence building bridges became
mandatory for infrastructure development. During the
ancient time natural bridges were created by nature as in
tree trunks extended to the inaccessibleareas.Thenhumans
started building their artificial bridges to travel tootherside
of the valley or non transportable point. The bridges built by
humans were usually made of wood or bamboo thatch. As
the population increased the need for bigger and sturdier
bridge was more. This led for innovation in bridge building
techniques thus many types of bridges were formed.
There are many classifications of bridges. The
bridge which is under study is girder bridges subjected to
some radius of curvature that is also known as curved
bridge. The curvature in the bridges is usually introduced to
eliminate the support irregularitiesorpresenceofimportant
structures which cannot bedemolished.Duetothecurvature
in the bridge there will be large centrifugal reactions on the
vehicles. Apart from the reaction a large torsional moment
will be induced on the supporting girders. Box girders
greatly reduce the torsional moment giving greater stability
to the structure. The columns locationandorientationisalso
a major design category in bridges. When the columns are
tilted from the normal angle the column issaidtobeskewed.
Skewed column decreases the stability of structures as seen
in the previous literatures.Skewedcolumns alongwithsome
degree of horizontal curvature to the bridges create a lot of
instability. The design of such bridges is always governed by
code books and designed verycarefully.Thestudydealswith
bridges subjected to seismic loads and itsbehavior whenthe
bridge is curved horizontally at deck section and skewed at
column or pier section.
The bridge will be subjected to many kinds of loads
such as earthquake, wind and vibration loads created by the
live load on the bridge.
1.1 Seismic loads
Seismic loads create a large impact onthestructure.
Ground motions are typically measured and quantified in
three primary directional components. Two of these
components are orthogonal and in the horizontal plane,
while the third component is in the vertical direction. The
vertical component of ground motion is known to attenuate
faster than its horizontal counterparts.Therefore,theimpact
of vertical ground motion on a bridge structure is typically
minimal for bridges located at distances approaching 100
km from active fault. For structures in moderate-to-high
seismic regions and close proximity to active faults (<25
km), the vertical component of ground motion is muchmore
prominent, and may be damaging in parallel with horizontal
components.
1.2 Vehicle loads
For live load purposes vehicular load is taken asthe
live load on the bridge. The load of vehicles is taken
according to the IRC 6. There are 3 types of standards types

 IRC class AA
 IRC class A
 IRC class B
Class AA – This type of class is a tacked vehiclewith70tonne
weight or a wheeled vehicle with 40 tonne weight as shown
in the figure.
Class A – wheel load train composed of a driving vehicle and
two trailers of specified axle spacing’s.
Class B is loading of temporary structure and for bridge in
some special cases.
Figure 1 - Class 70 R wheel load
Figure 2 - Class A wheel load
Figure 3 - Class B wheel load
2. OBJECTIVE OF THE PROJECT
 To study the behavior of Box girder bridge
subjected to various parameters such as radius of
curvature (inf, 250m, 150m) and skewness of
column (0, 15, 30) when it is subjected to seismic
loading.
 To study the behavior of I girder bridgesubjectedto
various parameters such as radius of curvature (inf,
250m, 150m) and skewness of column (0, 15, 30)
when it is subjected to seismic loading.
 Comparison between both the bridge I girder
Bridge and Box girder bridge.
3. METHODOLOGY
3.1 General
This chapter emphasizes on the method used to
study the behavior of curved bridges. The detailsofsoftware
used and the steps followed for analysis is dealt in this
chapter.
3.2 Methodology adopted
 The models of the bridge are createdinthesoftware
for analysis. Loads are applied to structure
including self weight, vehicle load and seismic load.
 Linear static analysis is carried out on the structure
and results are noted.
 Then the parameters of study are changed and
model is prepared again.
 Analysis is done and results are tabulated.
 The process is repeated for all the models.
 Comparison of the results is done and safe
combination is determined.
3.3 Description of model
The software used for modeling and analysis is CSI
BRIDGE. The components of bridge are
 Foundation
 Abutments
 Columns
 Column cap
 Bearings
 Support structure
 Deck
 Spans
 Lanes
Inputs given in the software for the components are
1. Foundation – The foundation will be considered as
spread footing fixed. No changes will be made in
this part of the bridge.
2. Abutments – Abutments are constructed near the
solid surface or a rough definition would be corner
columns. The dimensions given are 1.2m in width
and 2.5 in depth.
3. Columns – Columns will be made up of concrete
M30 grade. Will be circular in shape. Fe 500 steel
will be used for reinforcement. The diameter of the
columns considered is 1.5m.
4. Column Cap – A beam which connects the columns
and supports bridge support structure is column
cap. The width cap is equal to the diameter of
columns which is 1.5m and depth of 1.5m equal to
bridge support girder.

5. Bearing- All the translational degree of freedomare
fixed and not allowed to move where as the
rotational degree of freedom is kept free.
6. Support structure – 2 types of bridge support
girders will be analyzed. First with multi frame box
girder and second with I girder. The depth of each
will be kept constant equal to 1.5m. width is box
girder will be equal to that of deck.
7. Deck – Deck will be made up of concrete M30 and a
depth of 300mm.
8. Spans – 2 spans of 50m each will be analyzed for
vehicle and seismic loads.
9. Lanes – 2 lanes each of 3.75m with an offset of 1m
in between will be modeled.
3.3 Parameters under study
The following parameters will be varied
1. Column skewness – The skew angle is the angle with
which a column is rotated to accommodate the bridge.
The skew angle will be varied in 0, 15, 30 degrees and
analyzed accordingly.
2. Span curvature – The span will be analyzed for straight
bridge(R=inf) and 2 curved bridges (R=150m and
250m)
3. Support structure – 2 types of supports will be
considered
1. Concrete Box girder
2. I girder
Figure 4 - Cross section of Bent Section
Figure 5 – Cross-section of Box girder
Figure 6 – Cross-section of I girder
3.4 Loading pattern
1. Vehicle load – Load is applied according toIRCA,IRCAA
and IRC 70 R wheel load.
2. Seismic load – The region under consideration is
Mangalore with Seismic zone factor z = 0.16 and soil
zone III with following periods and acceleration.
Table -1: Loading pattern of response spectrum for the
above soil and zone
Period Acceleration
0 0.16
0.1 0.4
0.67 0.4
0.8 0.334
1 0.2672
1.2 0.2227
1.4 0.1909
1.6 0.167
1.8 0.1484
2 0.1336
2.5 0.1069
3 0.0891
3.5 0.0763
4 – 10 0.0668

4. RESULTS AND DISCUSSION
The models were analyzed separately and results
were noted. The results were compared.
4.1 Analysis of straight bridge
Inputs given
1. R= infinity, 150m, 250m
2. Span length between supports = 50m
3. Column skewness = 0, 15, 30
Figure 7 - 3D View of Straight Bridge
Figure 8 - 3D view of Curved Bridge (250m)
Figure 9 - 3D view of Curved Bridge (150m)
4.2 Modal Analysis results were tabulated and
compared with other models.
The bridge was modeled for Box girder and I girder
with varying radius of curvature(inf, 250m, 150m) and
column skewness (0, 15, 30) and subjected to seismic load.
The modal period for first transversal and longitudinal
vibrations were tabulated and compared.
Table -2: Period of first transversal vibration mode in
seconds for skew angle and radius of curvature
Angle
of
Skew
Box Girder Bridge I Girder Bridge
Inf 250 150 Inf 250 150
0 0.8271 0.82817 0.75152 1.22245 1.19279 1.19171
15 0.82817 0.81099 0.73417 1.21593 1.18736 1.18599
30 0.83715 0.73799 0.71744 1.19188 1.16818 1.6681
Table -3: Period of first longitudinal vibration mode in
seconds for skew angle and radius of curvature
Angle
of
Skew
Box Girder Bridge I Girder Bridge
Inf 250 150 Inf 250 150
0 0.51653 0.52496 0.53697 0.83891 0.83069 0.84938
15 0.51651 0.50960 0.53237 0.83767 0.82830 0.84964
30 0.50432 0.50773 0.50155 0.8280 0.81952 0.83617
4.3 Pushover analysis (Non linear analysis)
Response spectrum analysis was carried out
according IS 1893 2002 with the seismic zone and soil type
as mentioned in methodology. As bridge structures are
subjected horizontal reactions a non linear pushover
analysis will be conducted on the bridge models. The below
results show the pushover analysis of the straight bridge,
curved bridge (150m and 250m)subjectedtoskewnesswith
different supporting girders.
4.3.1 Results of box girder bridge
Chart 1 - pushover graph for 0 degree skew.

Chart 4 - pushover graph for straight bridge with
varying skew.
4.3.2 Results of I girder bridge
Chart 7- pushover graph for 30 degree skew.
Chart 8 - pushover graph for straight bridge with
varying skew.
4.3.3 Comparison between I girder bridge and box
girder bridge
Chart 9 - pushover graph for straight bridge.

Chart 10 - pushover graph for 150m curved bridge.
Chart 11 - pushover graph 250m curved bridge.
Figure 18 - pushover graph 250m curved bridge.
Chart 15- pushover graph 250m curved bridge.

4.4 Discussion of results
1. By the modal analysis results we can see that as the
radius increases there is decrease in transversal
vibration period. This is due to formation of a couple
at column section which opposes the transversal
vibration.
2. Compared to Box girder, I girder’s vibration in both
transversal as well as longitudinal vibrations are
greater.
3. As column skewness increases there is increase in
transversal vibrations and decrease in longitudinal
vibrations.
4. The pushover analysis results show that as radius of
curvature increases the basereactionsdecreases.This
indicates for high radius of curvature the bridge is
more stable.
5. For box girder and I girder bridge the max base
reaction for the straight bridge for degree of
skewness.
6. Pushover graphs showed only marginal differences
when a straight bridge with different skewness was
compared.
7. Box Girder Bridge showed better performance in
pushover analysis than I GirderBridgeforall thethree
types of radius of curvature and for all the different
skewness.
5. CONCLUSION
From the results we can conclude that the Box girder
bridge is more stable and sustainable compared to I girder
bridge when subjected to seismic loading. The effect of
radius of curvature is large in reduction of base reaction.
This is substantially large thus increasing the risk of the
structure. Effect of skewness on the base reaction was very
less and showed very little importance. But the combined
effect of both radius and skewness is matter of concern.
Straight bridge showed better results in pushover analysis
hence proving to be more stable than the curved bridge.
Hence provision of radius of curvature should be carefully
designed when the bridge is subjected to seismic loads.
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