International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 7 - October 2015
Comparative Study on the Seismic Performance of Integral and
Conventional Bridges
Lakshmy Kakkanatt. U#1, Rajesh. A. K*
#
PG Student, Department of Civil Engineering, Ilahia College of Engineering and Technology, Muvattupuzha, Kerala, India.
*Assistant Professor, Department of Civil Engineering, Ilahia College of Engineering and Technology, Muvattupuzha, Kerala,
India.
Abstract—In conventional construction of bridges, the
superstructure consists of a series of simply supported spans
separated by expansion joints and resting on bearings at the
abutments and intermediate piers. But during in-service life of
bridges, these joints and bearings become potential places for
accumulation of debris and deicingchemicals, thereby
deteriorating concrete and corroding steel reinforcements that
lead to high life cycle cost including maintenance cost. Hence,
engineers have recommended constructing bridges without
joints, to reduce the initial and maintenance costs. Thus
integral and semi integral bridges arise. This paper presents
comparison on the seismic performance of conventional, semiintegral and integral bridges using finite element tool i.e.,
ANSYS. ANSYS help in finding seismic behaviour these
bridges. Displacement and stress results are also analysed
and compared.
Keywords—bearings, conventional bridges, integral bridges,
joints, semi-integral bridges
I. INTRODUCTION
A bridge is a structure that crosses over a river, bay, or other
obstruction, permitting the smooth and safe passage of
vehicles, trains, and pedestrians. A bridge structure is divided
into an upper part (the superstructure), which consists of the
slab, the floor system, and the main truss or girders, and a
lower part (the substructure), which are columns or piers,
towers, footings, piles, and abutments. To allow free
expansion and contraction between superstructure and
abutments, the traditional construction method has
incorporated joints and bearings [1].The expansion joints and
bearings, by virtue of their functions are sources of weakness
in the bridge and there are many examples of distress in
bridges, primarily due to poor performance of these two
elements.As a way to reduce initial and maintenance cost,
engineers recommend building bridges without joints [1].
Such bridges are known as integral bridges. The primary
purpose of monolithic construction is to eliminate the need for
deck movement joints and bearings at abutments [2]. The
main difference between an integral bridge and a conventional
bridge is the manner in which movement is accommodated. A
conventional bridge accommodates movement by means of
sliding bearing surfaces. An integral bridge accommodates
movement by its flexible foundation. One of the most
common problems in the seismic resistance of traditional
bridge construction is unseating of the superstructure from the
ISSN: 2231-5381
support bearings [3]. This problem can be eliminated in
integral abutment construction as there are no support
bearings. However, the system of joints and bearings used in
traditional construction allows superstructure movements
during a seismic event which result in a decreased demand on
the foundation. In integral abutment construction, the
foundation piles and abutment must be able to accommodate
these increased demands [3]. In this paper, 3 types of bridges
ie, conventional bridge (bridge with joints and bearings),semiintegral bridge (bridge with joints but no bearings) and
integral bridge (bridge with no joints and bearings) are
analysed in terms of seismic performance and displacement
and stress results are compared using finite element tool
ANSYS.
II. LITERATURE REVIEW
Wilson J.C. (1988) conducted a research study to assess
the effects of the stiffness of monolithic bridge abutments on
the seismic performance of IBs. In this study, a simple
analytical model was developed that describes the stiffness of
the abutments with six equivalent discrete springs for three
translational and three rotational degrees of freedom. These
springs are assigned various stiffnesses to include the effects
of the abutment wall, pile foundations and soil. However,
inertial effects arising from acceleration of the abutment and
backfill mass during the excitations caused by an earthquake
was not considered in this model [4].
Spyrakos and Loannidis (2003) have conducted a research
study on the seismic behaviour of IBs. In this study, the effect
of soil structure interaction on the seismic performance of IBs
was evaluated. Linear elastic half space theory and a two-step
approach were utilized to simulate the effect of soil structure
interaction. The analytical model was also validated with field
measurement. However, the nonlinear effects of soil-structure
interaction were neglected and a single direct analysis
technique that models the whole system including the
superstructure, substructure and soil was not used due to its
complexity [5].
Robert J. Frosch, Michael E. Kreger, Aaron M. Talbott
(2009), conducted a study to evaluate the response of integral
abutment bridges to seismic loading. For this, field
investigation, analytical investigation and laboratory
investigation were conducted.Results of the field, analytical,
and laboratory investigations were used to evaluate allowable
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bridge lengths based on seismic performance. Finally, design
recommendations are provided to enhance the seismic
performance of integral abutment bridges [3].
Ahmad M. Itani and Gokhan Pekcan (2011) investigated
about seismic performance of steel plate girder bridges with
integral abutments. Analytical investigations were conducted
on computational models of steel bridges with integral
abutments to determine their seismic behaviour as a system
and to develop seismic design guidelines. Based on the
analytical investigations and available experimental research,
guidelines for the seismic analysis and design of integral
abutment bridges were developed [6].
terms enable the elements to analyse flexural, lateral, and
torsional stability problems. Elasticity, plasticity, creep and
other nonlinear material models are supported. A cross-section
associated with this element type can be a built-up section
referencing more than one material.
B. Material Properties
Three materials are defined to model the bridge. They are
concrete, steel and neoprene. Table I provides the properties
such as elastic modulus, Poisson’s ratio and density of the
materials.
V. TABLE I
MATERIAL PROPERTIES
III. MODEL DESCRIPTION
Effective span of bridge = 21.75m
Carriageway width =7.5m
Live load = IRC class A
Mix = M25
Footpath of 1500mm width is provided on both sides.
3 longitudinal girders are placed at a distance of 3m c/c.
Width of longitudinal girder = 0.3m
Thickness of deck slab = 0.24m
Piers and bed blocks are also provided.
IV. MODELLING OF CONVENTIONAL BRIDGE
For modelling of conventional bridge, two bridge spans
each having 22.32m length and separated by means of
expansion joints of 40mm are selected. Bearings are also
provided between the superstructure and piers.
A. Elements Used
1)Solid 65: It is used to model concrete. The element is
defined by eight nodes having three degrees of freedom at
each node: translations in the nodal x, y, and z directions. The
concrete element is similar to a 3-D structural solid but with
the addition of special cracking and crushing capabilities. The
most important aspect of this element is the treatment of
nonlinear material properties. The solid is capable of cracking
in tension and crushing in compression. Special features of
solid 65 are plasticity, creep, cracking, crushing, large
deflection and large strain.
2)Shell 181:Shell 181 is used to model piers. It is a fournode element with six degrees of freedom at each node: a
translation in the x, y, and z directions, and rotations about the
x, y, and z-axes. It is well-suited for linear, large rotation,
and/or large strain nonlinear applications. Change in shell
thickness is accounted for in nonlinear analyses. In the
element domain, both full and reduced integration schemes
are supported. Shell181 accounts for load stiffness effects of
distributed pressures.
Sl
No
Material
Elastic
Modulus
(N/mm2)
Poisson’s
Ratio
Density(N/mm3)
1
Concrete
25000
0.2
2.4×10-6
2
Steel
2×105
0.3
7.85×10-6
3
Neoprene
6
0.499
9.65×10-7
C. Modelling of Bearings
The elastomeric bearings, which are made of low damping
rubber (neoprene) where the behaviour is nearly elastic, are
idealized as 3-D beam elements connected between the
superstructure and the substructures at girder locations. The
height of the beam elements is set equal to the thickness of the
bearings. Size of bearing is taken as 500×360×99mm.
Thematerial used is neoprene. Shear modulus is taken as
1N/mm2 (IRC 83: part 2).
D. Modelling of Reinforcement
Smeared model method is used to model reinforcement.
The smeared model assumes that reinforcement is uniformly
spread throughout the concrete elements in a defined region of
the finite element mesh. This approach is used for large-scale
models. ANSYS allows the user to enter three rebar materials
in the concrete. Each material corresponds to x, y, and zdirections in the element. The reinforcement has uniaxial
stiffness and the directional orientation is defined by the user.
3 sets of real constants are used. Table II shows smeared
model parameters required to model reinforcement.
3)Beam 188: Beam 188 is used to model bearings. It is
suitable for analysing slender to moderately stubby/thick
beam structures. The element provides options for
unrestrained warping and restrained warping of cross-sections.
The element includes stress stiffness terms, by default, in any
analysis with large deflection. The provided stress-stiffness
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elements, or all hexahedral (brick) volume elements to
generate a mapped mesh.
VI. TABLE II
SMEARED MODEL PARAMETERS
Constants
Real
Element
Constants
Type
Particulars
Set
Material
Real
Real
Constant
Constant
For
For
Rebar 1
Rebar 2
2
2
0.0327
0.00453
90
0
0
90
0.000994
0.001211
90
0
0
90
0.00302
0.00116
F. Boundary Conditions
Displacement boundary conditions are needed to constrain
the model to get a unique solution. To ensure that the model
acts the same way as the experimental bridge, boundary
conditions need to be applied at points of symmetry and where
the supports and loadings 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].
Fig 1 shows the model of conventional bridge in ANSYS.
Volume
Ratio
1
Orientation
Angle θ
Orientation
Angle Φ
Volume
Solid 65
Ratio
Orientation
2
Angle θ
Orientation
Angle Φ
Volume
Ratio
Fig. 1. Model of conventional bridge.
Orientation
3
Angle θ
90
0
0
90
Orientation
Angle Φ
Volume ratios are calculated using the equation (1) given
below:
(1)
Where,
Where, d = Diameter of the rebar
Orientation Angle θ defines orientation measure from local
X to Y axis. Orientation Angle Φ is the angle measured from
local XY plane from X.
E. Meshing
Mapped mesh is used. For this, whole structure is divided
into small areas.In this meshing, we can specify that the
program use all quadrilateral area elements, all triangle area
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G. Loading and Analysis
Live load is taken as IRC class A. For maximum bending
moment on deck slab, the load with maximum intensity
should be placed symmetrically with respect to the centre.
Inorder to get the impact effect, the load is multiplied by
impact factor. It is given as point loads as per IRC 6:2000.
As it is known the design of bridges has to compromise
both its functional and earthquake resistant performance, as
they are conflictful components of the same problem and they
impose opposite design requirements. ANSYS uses the
Newton-Raphson approach to solve nonlinear problems. Here
for seismic loading Ahmadabad Frequency Response
spectrum (FRS) is taken into consideration. It consists of
frequency and acceleration. Reciprocal of frequency gives
time in seconds. Thus transient analysis can be done by
entering time and acceleration as inertial loads. The main
difference between the static and transient procedures is that
time-integration effects can be activated in the transient
analysis. Thus, "time" always represents actual chronology in
a transient analysis.
VII. MODELLING OF SEMI-INTEGRAL BRIDGE
Modelling of semi-integral bridge is same as that of
conventional bridge. Difference is that bearings are eliminated.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 7 - October 2015
But 40mm joints are provided between the spans.
VIII. MODELLING OF INTEGRAL BRIDGE
Integral bridges act as a rigid structure. It minimizes the use
of bearings and resists large lateral forces. So for the
modelling of integral bridge joints and bearings are eliminated.
Integral bridge requires flexible foundations to accommodate
stresses produced from lateral forces. Inorder to maintain
flexibility, the boundary conditions are set to restrain
movements in vertical direction and accommodate the
movements in horizontal direction. Fig 2 shows the model of
integral bridge.
Fig. 2. Model of integral bridge
IX. RESULTS AND DISCUSSIONS
Table III shows deformation and stress results obtained
after analysis.
X. TABLE III
DEFORMATION AND STRESS RESULTS
SemiParameters
Conventional
Integral
Integral
Bridge
Bridge
Bridge
Displacement (mm)
22.2943
17.4314
10.0279
Stress (MPa)
69.5941
66.7591
60.259
From the table we can understand that, deflection obtained
for conventional bridge, semi-integral bridge and integral
bridge are 22.2943mm, 17.4314mm and 10.0279mm
respectively. It is found that integral bridge has smaller
deflection when compared to other bridges due to its rigid
nature. Deflection limit of a concrete bridge (including
footpath) is
. Here all the
deflections are within the limit.
integral bridge and integral bridge are 69.5941Mpa,
66.7591Mpa and 60.259Mpa respectively. Here also stress
obtained for integral bridge is less than other bridges.
So earthquake resistance of the bridge can be enhanced by
using monolithical systems. With respect to seismic
performance; increased redundancy, smaller displacements
and elimination of unseating potential are main benefits of
integral bridges over conventional bridges [6]. Integral
construction provides increased seismic resistance with
respect to traditional construction due to increased redundancy
and continuity. Joints introduce a potential collapse
mechanism into the overall bridge structure in conventional
construction [6]. Integral abutments eliminate the most
common cause of damage to bridges in seismic events, loss of
girder support [1]. In integral bridges functional movements
are maximized at the ends of the continuous deck where the
monolithical connection of the abutment or pier with the deck
is, while the central piers being usually higher and as such,
more tolerant to deformations, experience lower
displacements. Abutment flexibility was an important element
in earthquake design of integral bridges. A more flexible
abutment would lead to higher deformation demands on the
other components along the lateral load path.
Integral bridge takes the advantage of the inherent ability
of reinforced concrete to dissipate part of the induced seismic
energy by hysteretic behaviour while their redundancy is high
[7]. Implementation of rigidly supported abutments or piers on
integral bridges can be seen as a promising solution for the
reduction of the seismic displacements of particular bridge.If
the length of bridge is greater, intermediate joints will be
provided with bearings to allow horizontal movements. But
these joints will be lesser in numbers as compared to
traditional construction. But it is well suited for small and
moderate length bridges.
XI. CONCLUSIONS
In this paper, conventional, semi-integral and integral
bridges were modelled and transient analysis is done using
finite element tool ANSYS. Elimination of bearings improves
the structural performance of integral bridges due to
earthquake and it requires less inspection and maintenance
efforts. It is found that integral bridge has smaller deflection
and stress when compared to other bridges due to its rigid
nature. Due to their increased stiffness, these bridges exhibits
lower displacement demands. In integral bridges functional
movements are maximized at the ends of the continuous deck.
Unseating of superstructure from the support bearings can be
eliminated. Therefore, integral bridges can be seen as a
promising solution for the reduction of the seismic
displacements.
Further investigation, concerning soil structure interaction
and temperature effects are necessary in order to study the
interaction between the main parameters of the problem.
In case of stress, Von Mises stress results are taken. The
Von Mises stress obtained for conventional bridge, semi-
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 7 - October 2015
ACKNOWLEDGMENT
The authors wish to acknowledge the support received
from the Ilahia College of Engineering And Technology,
Muvattupuzha in connection with this work.
REFERENCES
[1] Vimala Shekar,Srinivas Aluri, Dr. Hota V.S.,GangaRao, ―Integral
abutment bridges with FRP decks – case studies‖,in The 2005 – FHWA
Conference, 2005, p. 113.
[2] Integral abutment bridge design guidelines, VTrans, Integral Abutment
Committee, 2nd Edition, 2008.
[3] Robert J. Frosch, Michael E. Kreger, Aaron M. Talbott,“Earthquake
resistance of integral abutment bridges‖, INDOT Office of Research &
Development, Report No: FHWA/IN/JTRP-2008/11, 2009.
[4] Wilson.J.C. ―Stiffness of non-skew monolithic bridge abutments for
seismic analysis‖Earthquake Engineering and Structural Dynamics, vol. 16,
pp: 867–883, 1988.
[5] Spyrakos, C. and Loannidis, G,―Seismic behavior of a post-tensioned
integral bridge including soil-structure interaction (SSI)‖.Soil Dynamics and
Earthquake Engineering, vol. 23, pp 53-63,2003.
[6] Ahmad M. Itani and Gokhan Pekcan, ―Seismic performance of steel plate
girder bridges with integral abutments”, Fedral Highway Administration,
Report No: FHWA-HIF-11-043, 2011.
[7] Ioannis Tegos, Anastasios Sextos,‖ Contribution to the improvement of
seismic performance of integral bridges‖, unpublished.
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