seismic analysis of railway bridge … · soil-structure interaction under seismic loads is a...

4th International Conference on Earthquake Engineering and Seismology

11-13 October 2017 – ANADOLU UNIVERSITY – Eskisehir/TURKEY

SEISMIC ANALYSIS OF RAILWAY BRIDGE CONSIDERING

SOIL-STRUCTURE INTERACTION

Abdul Ahad FAIZAN1and Osman KIRTEL

2 1Master Student, Civil Eng. Department, Institute of Natural Sceince, Sakarya University, Sakarya, Turkey 2Assistant Professor, Civil Eng. Department, Faculty of Technology, Sakarya University, Sakarya, Turkey

Email: [email protected]

ABSTRACT:

This paper presents an investigation of dynamic behavior of an existing railway bridge in Turkey, subjected to

earthquake. In this study earthquake response characteristic of a multi span railway bridge was analyzed. Time

domain dynamic analyses of the structure-soil model and also a 2D version of PLAXIS, a specially developed

finite element software for solving geotechnical problems, have been performed. In the analysis, two dimensional

finite element (FE) model was used. Considering the soil property of bridge site, analysis was performed for three

types of soil; the soils were specified as a soft, medium and dense.Kocaeli earthquake is defined as input motion

for dynamic load. According to the result of the dynamic analysis, the relative horizontal displacement graphs for

the top point of bridge (Point A) were prepared and showed as a graphic form. The analysis with PLAXIS 2D

demonstrated that for different conditions delimitation, distribution of travel and the fundamental frequency for

each soil type change according to its mechanical properties. The obtained results show that it is necessary to take

into account the phenomenon of structural soil interaction in the bridge analysis and also demonstrates that the

proximity of the fundamental frequencies of the structure and soil strongly influences on soil-structure interaction.

KEYWORDS: Railway Bridge, Soil-Structure Interaction, Seismic Behaviour, Finite Element Method.

1. INTRODUCTION

Railway Bridges are very important elements of the infrastructure in modern societies and form an important

transportation link in the railway network of a country. In modern transportation facilities it demands that the

bridges are to be constructed across the seismically active regions and also at the same time the site conditions

impel the researchers to rest the pier foundation of the railway bridges on soil. Due to railway bridge importance,

functionality loss of these type bridges after a seismic event is not an acceptable performance criterion for those

structures. Therefore, maintaining and safety of the railway bridge in seismic areas is of great importance for post-

earthquake relief operations. The failure of the railway bridge foundation and substructure in earthquake is one of

the most common cause of damage of the structure.

Study of the dynamic response of railway bridges to seismic actions has reached a great interest because the

amount of bridges/railway bridges failures which have happened in recent earthquakes. In the past, many railway

bridges have suffered extensive damage due to strong motion earthquakes and failure of railway bridges due to

complete collapse of foundation piers has been observed in major seismic events. The San Fernando earthquake

(1971), Hyogoken-Nanbu (Kobe) earthquake (1995), Kocaeli earthquake (1999), Loma Prieta earthquake (1989),

Chi-Chi earthquake (1999) and Northridge earthquake (1994) have demonstrated that near-field ground motions

can potentially destroy and can severely impact urban infrastructure such as bridges when the causative fault is in

the immediate vicinity of a large metropolitan area. These earthquakes alarmed the bridge engineers which started

looking toward alternative design methods and sufficient dynamic analyses to minimize the seismic risk on bridge

structures for protection of bridges from severe earthquake attacks.



There had been several studies in the past for the dynamic behavior (especially to seismic actions) of train-

bridge coupling systems. Wu and Yang (2002) carried out a dynamic response analysis of train-bridge systems

subjected to uniform seismic ground motions. Miyamoto et al. (1997) studied the dynamic responses of the

Shinkansen train-bridge systems to seismic excitations. Du et al. (2011) and Xia et al. (2006) presented a dynamic

analysis of train-bridge systems subjected to seismic ground motions considering wave passage effect.

Among many other aspects soil structure interaction (SSI) is an important aspect which must be taken into

account in the dynamic modelling of the railway bridge structures. The seismic evaluation of major long-span

elevated bridges typically requires consideration of dynamic soil-structure interaction effects on the seismic

response of such bridges. Consideration of soil-structure interaction effects is extremely important for determining

the seismic response of bridges and it allows researchers and practicing engineers to design more seismically

resilient bridges (M. Baheddi and Y. Youb 2015). Soil-structure interaction under seismic loads is a highly non-

linear phenomenon and plays important role in the overall structural response (Maragakis 1989). Therefore it needs

to develop a proper and sufficient methodology to analyse and design railway bridges including the effects of soil-

structure interaction.

The earthquake resistance of railway bridges locate in seismically active regions such as Turkey is very

important. Determination of the soil properties accurately and taking them into account when dynamic analysis

provides an important contribution for understanding the behaviour of bridge structures under earthquake

conditions. During earthquake, due to the different responses of the soil and bridge, the bridge pier affects the

behaviour of the soil and the soil affects the behaviour of bridge pier. Bridges subjected to earthquake effect move

with the soil and the soil changes the dynamic behavior of the bridge structure such as mode shape and period.

Due to the importance of the soil-structure interaction (SSI), the earthquake regulations included on the agenda

for soil-structure interaction analysis in Turkey (TEC 2007).

Many researchers have studied the influence of soil-structure interaction on the earthquake response of

conventionally designed bridges in recent years. Spyrakos (1990, 1992) utilizing linear elastic models have

identified the significant role of soil–structure interaction during seismic excitation of non-isolated bridges and

have showed that SSI greatly affects the seismic response of bridges leading toward more flexible systems and

increased damping. Pinto and Ciampoli (1995) investigated the conventionally designed bridge considering

inelastic response of the piers which was built on shallow foundation types. Seven artificially generated

accelerograms compatible to Eurocode No. 8 spectra for far field type of excitations and for intermediate stiffness

type soils consisted in the seismic input. From the obtained results they concluded that soil-structure interaction

effects consistently decreased the ductility demands of the bridge piers when it compaered to the system which is

soil-structure interaction didn’t consider. Gazetas and Mylonakis (2000) considering a set of actual acceleration

time histories recorded on soft soil and using a simplified model for the bridge and the foundation showed that the

period lengthening and increased damping due to soil-structure interaction effects can have a detrimental effect on

the imposed seismic demands. Jeremic et al. (2004) documented a detailed finite element study on the seismic

response of the I-880 viaduct which is located in Oakland, Calif. The conclusions of this study was as the same

conclusions as Gazetas and Mylonakis (2000). According to the obtained results, it concluded that soil-structure

interaction can have both detrimental and beneficial effects on the response of the structure depending on the

characteristics of the ground motion.

From these evidences it has been well recognized that influences of SSI are very important for the seismic

responses of railway bridges. Also considerable interest was concentrated on the soil-structure interaction effects

of such structures through model experiments and theoretical analyses.



Figure 1.Nishinomiya-ko Bridge approach span collapse in the 1995 Hyogo-Ken Nanbu (Kobe) earthquake

(Kobe Collection, EERC Library, University of California, Berkeley)

2. SCOPE AND OBJECTIVE

The objective of the present research is to analyse the dynamic behavior of an existing railway bridge in Afyon

(Turkey), subjected to earthquake considering soil-structure interaction (SSI). Analysis was performed for three

types of soil (soft, medium and dense) and Kocaeli earthquake is defined as input motion for dynamic load. Then

a comparative study of the displacements for these three types of soils has been performed. According to the results

of the dynamic analysis, the relative horizontal displacement graphs for the top point of the bridge (Point A) were

prepared for each type of soils and showed as a graphic form. It is expected that the findings of the present study

will lead to a better understanding of the dynamic behavior of railway bridge under seismic loading.

3. DESCRIPTION OF THE CASE STUDY

General and a two dimensional isometric view of the continuous four-span deck girder railway bridge is shown in

Figure 2 with dimensions and boundary conditions. The model of the bridge has a total span length of 128m.

Column height is taken as 7.38m and the superstructure consists of a main girder of 3.25m deep and 12m wide.

The soil surrounding the pier of Railway Bridge is considered as soft, medium and dense. The seismic response

of railway bridge system is investigated for one type of earthquake. Kocaeli (Turkey, 1999) is defined as input

motion. The concrete class of the proposed railway bridge is C30.



(a)

(b)

Figure 2. (a) General and (b) 2D views of the proposed Railway Bridge

4. FINITE ELEMENT MODELING

A two dimensional modeling of the railway bridge has been done by using finite element analysis software

PLAXIS 2D. A 2D view of the finite element mesh is shown in Figure 3. For determining of the finite element

model dimensions many analyses were employed in the past and it is suggested that these boundary areas must be

as far at least 8-10 times of the superstructure base width (Rosset et al. 1976). In the present study, in addition to

the existing information, two dimensional (2D) plane strain analyses of soil were employed to find the sufficient

soil dimensions for soil-structure analyses. In this study, discretization of the finite element model of the soil area

has been made by taking into account the absorbing boundary conditions. Firstly, the effect of wave propagation

on the horizontal expansion of the soil model was investigated by keeping the height of the soil model constant (H

= 60 m). According to the time-displacement relationships results obtained from the points where the wave

propagation is controlled, it is concluded that L = 300 m is sufficient. After determining the horizontal expansion

of the finite element model of the soil area (L = 300 m), the effect of the wave propagation on the height of the

soil model was also investigated. According to the time-displacement relationships taken from the points where

the wave propagation is controlled, it is concluded that it is sufficient to choose H = 85m and ∆h = 4m. According

to analyses results the finite element model dimensions of the soil component were chosen as 300 m by 85 m. The

mesh of the remaining subzones (hereby, H1 = 20 m, L1 = 80 m; ∆h1 = 1 m → H2 = 52 m, L2 = 190

m; ∆h2 = 2 m) are used in the modeling.



Figure 3. Soil-Structure Model

In this study we assume plane strain conditions, that is, all frames parallel to the plane of calculation in Figure 3.

deform identically. In the present study for 2D analysis of bridge-soil system, a 15-node triangular is chosen

(Figure 4.). This element is powerful and provides an accurate calculation of strains and stresses.

Figure 4. Position of nodes and stress points in soil elements

(Brinkgreve et al. 1998)

5. SEISMIC ANALYSIS OF THE RAILWAY BRIDGE

a) General form of Soil-Structure Model

b) PLAXIS 2D Finite Element Mesh



Dynamic behavior of the railway bridge specially to seismic actions and time history analyses of the soil- structure

models were carried out. The arrangement of the analyses is based on a simplified model of a railway bridge which

is located in Afyon, Turkey. As the purpose of this study, the example of the Afyon Railway Bridge is used to set

up the numerical model by taking into account absorbing boundary conditions. The seismic response of railway

bridge system is investigated for the one type of earthquake taken from the PEER NGA database

(http://peer.berkeley.edu/nga). Kocaeli (Turkey, 1999) earthquake is defined as input motion in seismic analysis

(Figure 5.). The properties of this earthquake ground motion are shown in Table 1.

Figure 5. Acceleration Record of Kocaeli Earthquake

Table 1. Properties of the earthquake ground motion

Earthquake Date Station Magnitude Peak acceleration

(g)

Resonance

Frequency (Hz)

Kocaeli 17-08-1999 KOCAELI/SKR090 7.4 0.35 0.29

In order to determine the dynamic behavior of the bridge pier-soil system, analyiss is carried out for different soil

conditions with different stiffnesses. According to the results of the dynamic analysis, the dynamic responses of

the bridge, including the horizontal displacements for the top point of the bridge pier for different types of soils

are obtained comparatively and showed in graphic forms. Considering the soil property of railway bridge site,

analysis was performed for three types of soils. To create the substructure soil models, railway bridge site soil was

selected as soft, medium and dense. The properties of the soils are given in Table 2.-Table 4. (Dave et al. 2006).

As a first approximation of soil behavior, Mohr-Coulomb model is used in general. The Mohr-Coulomb model

represents a first-order approximation of soil behavior and it is recommended to use this model for the analysis of

the problem considered. The model involves five parameters. These parameters are Poisson's ratio (ν), Young's

modulus (E), the friction angle (ϕ), the cohesion(c) and the dilatancy angle (ψ).

Table 2. Properties of the soft soil for undrained Mohr–Coulomb model

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 5 10 15 20 25 30 35

Acc

eler

ati

on

(g

)

Time (s)

Kocaeli Earthquake, 1999



Parameter Symbol Magnitude Unit

Total unit weight γ 16.68 (kN/m3)

Young’s modulus E 15000 (kN/m2)

Shear modulus G 5434.8 (kN/m2)

Poisson’s ratio ν 0.38 -

Compression wave velocity Vp 128.4 m/s

Shear wave velocity Vs 56.51 m/s

Cohesion c 25 (kN/m2)

Friction angle ø 35 (ο)

Dilatancy angle ψ 0 (ο)

Interface strength reduction factor Rinter 0.67 -

Table 3. Properties of the medium soil for undrained Mohr–Coulomb model




Shear modulus G 11950 (kN/m2)








Table 4. Properties of the dense soil for undrained Mohr–Coulomb model




Shear modulus G 27780 (kN/m2)










For numerical analysis, analytical models were developed by Finite Element Method (FEM). Different analyses

were performed on Railway Bridge system in terms of comparative results. The dynamic behaviour of bridge pier-

soil systems is observed and the comparative results are presented. In the present study, earthquake-induced wave

propagation problem with SSI effects is directly analysed by employing a two-dimensional finite element model

under plane-strain condition considering elasto-plastic Mohr–Coulomb constitutive law. For this purpose, the soil-

structure model was defined using the PLAXIS 2D and finite element method (Brinkgreve et al. 2002). By

inputting the Kocaeli earthquake acceleration to the bridge system, the behavior of the bridge-soil undere this

earthquake was invistigated (Figure 6.) and dynamic responses of the bridge, including the horizontal

displacements of the top of the railway bridge (Point A) were calculated by the PLAXIS 2D program for each type

of soils. According to the results of the dynamic analysis, the relative horizontal displacement graphs for the top

point of the bridge (Point A) were prepared for each type of soils and showed as a graphic form (Figure 7.).

Figure 6. Behavior of the soil-structure system under the influecne of Kocaeli earthquake

a) General form of Soil-Structure Model; b) Soft soil; c) Medium soil; d) Dense soil

Figure 7. Behavior of the bridge-soil system for different soil conditions

under the influence of Kocaeli earthquake

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

0 5 10 15 20 25 30 35

Dis

pla

cem

ent

Ux

[m

]

Dynamic Time (s)

Top point of the bridge (Point A) Soft Soil

Medium Soil

Dense Soil

(a) (b)

(c) (d)



6. RESULTS AND CONCLUSIONS

The main purpose of this investigation was to study the dynamic behaviour of a four-span continuous railway

bridge specially to seismic actions considering soil-structure interaction (SSI). Soil-structure interaction effects

under ground motion are directly accomplished by applying a two dimensional plane-strain finite element model

with elasto-plastic Mohr Coulomb approach. In this study, the goal was to develop an understanding of the seismic

response of a soil-bridge system for different types of soils under the influence of earthquake. In order to measure

the effect of ground motion as dynamic effect; time-acceleration record of Kocaeli (Turkey, 1999) earthquake is

used. In order to determine the dynamic behavior of the bridge pier-soil system to sesimic actions, analysis is

carried out for different soil conditions with different stiffnesses. Three types of soils were considered for analyses

and defined as soft, medium and dense. According to the results of the dynamic analysis, the dynamic responses

of the bridge, including the maximum horizontal displacements for the top point of the bridge pier for different

types of soils are obtained comparatively and showed in graphic form.

According to the obtained results, maximum horizontal displacements for soft soil, medium soil and dense soil

under the influence of Kocaeli earthquake are respectively 0.703m, 0.884m and 0.419m. Examining the results, it

was found that the maximum horizontal displacement of the top of bridge (Point A) for medium soil was

respectively 20.50% and 52.60% bigger than soft and dense soils.

The analysis with PLAXIS 2D demonstrated that for different conditions delimitation, distribution of travel and

the fundamental frequency for each soil type change according to its mechanical properties and it has been

observed that the frequency content of the external load and the mechanical properties of the soil largely affect the

dynamic behavior of the bridge pier and the maximum horizontal displacements differ when considering soil-

structure interaction. The obtained results show that it is necessary to take into account the phenomenon of

structural soil interaction in the bridge analysis and also demonstrates that the proximity of the fundamental

frequencies of the structure and soil strongly influences on soil-structure interaction.

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Du, X.T. Xu, Y.L. and Xia, H. 2011. Dynamic interaction of bridge–train system under non-uniform seismic

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Xia, H. Han, Y. Zhang, N. and Guo W.W. (2006). Dynamic analysis of train-bridge system subjected to

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Distributed by: A.A. Balkema Publisher, The Netherlands.

seismic analysis of railway bridge … · soil-structure interaction under seismic loads is a...

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