DYNAMIC ANALYSIS OF CONCRETE GIRDER BRIDGES UNDER STRONG EARTHQUAKES: THE EFFECT OF COLLISION, BASE-ISOLATED PIER AND WING WALL

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1 INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Online), Volume 6, Issue 4, April (2015), pp IAEME ISSN (Print) ISSN (Online) Volume 6, Issue 4, April (2015), pp IAEME: Journal Impact Factor (2015): (Calculated by GISI) IJCIET IAEME DYNAMIC ANALYSIS OF CONCRETE GIRDER BRIDGES UNDER STRONG EARTHQUAKES: THE EFFECT OF COLLISION, BASE-ISOLATED PIER AND WING WALL Desy Setyowulan 1, Keizo Yamamoto 2, ToshitakaYamao 3, Tomohisa Hamamoto 4 1 Graduate School of Science and Technology, Kumamoto University, Kurokami, Kumamoto, , Japan, 2 Department of Civil and Environmental Engineering, Kumamoto University, Kurokami, Kumamoto, , Japan, 3 Graduate School of Science and Technology, Kumamoto University, Kurokami, Kumamoto, , 4 Department of CivilEngineering, Gunma National College of Technology, 580, Tribamachi, Maebashi, Gunma , Japan, ABSTRACT This paper presents the dynamic analysis of concrete girder bridges taking into account the effect of collision on parapet wall. In addition, adopting of seismic isolation rubber on pier structure and wing wall on parapet were analyzed. Two spans concrete girder bridgeswith variation of gap were examined in theoretically by 3D FEM model of ABAQUS. The abutment was simplified by parapet wall which was modeled by 3D reinforced concrete structure. In order to examine the seismic behavior of bridge, six different inputs of seismic ground accelerations were applied at footing of pier structure.it has been suggested that allowing the collisionon abutment by restricting the girder bridges displacement, the size of expansion joints can be reduced in order to reduce the cost of construction and seismic reinforcement. According to the analytical results, it was found that installation of the wing wall had a capability for the horizontal displacement resistance. The seismic isolation rubber and the wing wall structure had a significant effect in reducing the response stress of parapet wall on small gap. Furthermore, cracking was also affected by the wing wall. Keywords:dynamic analysis, collision, gap, isolation rubber, concrete girder bridge, wing wall 79

2 I. INTRODUCTION Before 1995 Kobe earthquake, theconsideration of 10 cm gap has been used in the real bridge in Japan. However, several damages on bridges occurred, such as collision between adjacent decks and between deck and abutment. Consequently, collision becomes one of the important aspects to be evaluated in the seismic performance of the bridge. According to the seismic design by Japanese Specification of Highway Bridges, it has been determined that necessary gap between the ends of two adjacent girders shall be taken in the design of the superstructure for preventing any loss of the bridge caused by the collision between two adjacent superstructures, a superstructure and an abutment, or a superstructure and the truncated portion of a pier head, when a bridge is subjected to Level 2 Earthquake Ground Motion [1]. In the real bridges, gap varied from 20 cm to 50 cm. However, the adoption of large gap into bridge will increase the construction and seismic reinforcement cost since relatively large expansion joints have to be used. Previous study [2] has carried out an investigation on the dynamic behavior of concrete bridges with consideration of the pounding effect. The damage evaluation of abutment has been conducted by using 3-dimensional FEM. Pounding has been simulated by setting initial velocity on superstructure and applying 5 cases of impact velocities. In addition, frame analyses have been conducted in order to clarify the dynamic behavior of whole bridge by pounding. From this research, it has been confirmed that severe damage spreads over the entire parapet, the bottom of abutment and the wing wall abutment in case of impact velocity 3.0 m/s. An effect of large gap on the construction cost has been studied in another research [3]. The girder and pier have been modeled by beam elements considering the shock absorber in the end of girder. It has been found that attaching rubber shock absorber to the end of bridge girder reduce the response stress inthe end of girders and response rotation angle at the bottom of pier. Moreover, total costs of the proposed seismic reinforcement are 30% of that current seismic reinforcement. The behavior of concrete including the model verification of RC beam structures have been investigated by some researchers using the damage identification by Concrete Damaged Plasticity model in ABAQUS [4]. This code has shown to be an accurate method in performing nonlinear behavior of RC structure in comparison with the experimental results [5-8].In addition, elasto-plastic behaviors in abutments with four different approaches of the wing wall have been analyzed [9]. From this analysis, it has been found that installation of the wing wall had a capability in reducing the displacement of abutment. Moreover, the initial cracking occurred in the intersection between parapet wall and abutment wall. From previous study, it is noted that further study is needed in order to clarify the dynamic behavior of full bridges due to strong earthquake. However, the adoption of large gap will increase the size of expansion joint affected the high cost of construction and seismic reinforcement. It has been suggested that allowing the girder collision at the abutment by restricting the girder bridges displacement, the size of expansion joints can be reduced in order to reduce the cost of construction and seismic reinforcement. This paper presents the dynamic analysis of concrete girder bridges taking into account the effect of collision on abutment. In addition, adopting of base-isolated pier and wing wall on abutment were analyzed. Two span concrete girder bridge was examined in theoretically by 3D FEM model of ABAQUS. Parametric studies on dynamic analyses of bridges were investigated in 5 different gaps. Level 2 of earthquake ground motion was chosen as an input data in order to investigate its behavior under strong earthquake. Effect of soil pressure during earthquake was not taken into account. The numerical results represented that the parameters such as response stress, cracking distribution and displacement were affected by displacement restriction of girder, seismic isolation rubber and the wing wall. 80

3 II. NUMERICAL PROCEDURES 2.1 General description of analytical method The numerical modeling of bridge was conducted by using non-linear FE software, ABAQUS [4]. Collision phenomenon was simulated by setting 6 different waves of Type 2 input ground acceleration in X-direction at footing of pier, while the bottom of parapet wall was set to be hinged (U1=U2=U3=0). In this research, parametric study of bridges taking into account the effect of the wing wall and seismic isolation rubber at the bottom of pier were investigated, as shown in Fig. 1 and Fig. 2, respectively. The main parameter of this analysis was gap varied from 10, 20, 30, 40, and 50 cm parallel with Level 2 input of seismic ground accelerations. Two types of loads were applied in bridge; self-weight as a gravity load of 9.8 m/s 2 and the external load from seismic ground acceleration applied at footing of pier. In this modeling technique, the parapet wall, the reinforcing bars and the box girder superstructure were idealized by eight-node solid (brick) elements with reduced integration identified as C3D8R elements and three dimensional truss elements called T3D2 and linear shell elements called S4R. L=12m H=2.5m B=0.5m (a) Concrete element (b)rebar element Figure 1. Model with parapet only in the first analysis B=4m (a) Concrete element (b) Rebar element Figure 2. Model with parapet and wing wall in the first analysis 2.2 Analytical model of bridge An existing two spans concrete girder bridge adopted from the previous research [3] was studied. The total length of two span superstructures was 80.0 m with pier (P1) as its center. Parapet walls were located at both ends, depicted as A1 and A2. The bearing supports were fixed (F) and movable (M) at Pier 1 and both abutments, respectively. Figs. 3(a) 3(d) show the dimension and view of the real bridge. 81

4 (a) Side view of the bridge (b) Front view of P1 pier (c) Cross section of superstructure (d) Side view of P1 pier Figure 3. Dimensions of the bridge (unit: mm) In all modeling, it was assumed that no liquefaction occurred. Furthermore, constructing of seismic isolation rubber at bottom of pier structure, called as base-isolated pier, was developed in order to reduce the seismic response of abutment. The 3-dimensional FE models of bridge are shown in Figs. 4(a) and 4(b), respectively. (a) Without wing wall Figure 4. FE-modeling of bridge (b) Wing wall 2.3 Input seismic waves Level 2 earthquake ground motions were considered for taking into account in the dynamic analysis of bridge. Ground type I was chosen as representation of the real soil type, with six input seismic waves shown in Table 1 and Fig

5 Table 1. Acceleration waveform list Level / Type Earthquake name Nickname Abbreviation II / I 2003 Tokachi-oki earthquake I I 1 L2T1G1-1 Northeastern Pacific Ocean off the coast I I 2 L2T1G1-2 earthquake FY 2011 I I 3 II / II Hyogo-ken Nanu Earthquake 1995 II I 1 II I 2 II I 3 L2T1G1-3 L2T2G1-1 L2T2G1-2 L2T2G1-3 (gal) Ac c 度 0 (ga 速 -200 加 Time 時間 (s) (s) (gal) Ac c (ga 500 度速加 Time 時間 (s) (s) Ac c (ga (gal) 500 度速加 Time 時間 (s) (s) (a) Type I-I-1 wave (b) Type I-I-2 wave (c) Type I-I-3 (gal) Ac c (ga 500 度速加 時間 (s) Time (s) (gal) Ac c (ga 500 度速加 Time 時間 (s) (s) (gal) Ac c (ga 500 度速加 Time 時間 (s) (d) Type II-I-1 (e) Type II-I-2 wave (f) Type II-I-3 wave Figure 5. Input JSHB seismic waves Level II earthquake ground motions 2.4 Material properties and material model Material properties of bridges were shown in Table 2. In this analysis, rebar elements were treated as elasto-plastic model and concrete of parapet wall was developed by concrete damaged plasticity (CDP). Table 2. Material properties of the structure Pier Parapet Wall Bridge Material Properties Concrete Rebar Concrete Rebar girder Young's modulus (GPa) Poisson's ratio Density(kg/m 3 ) Compressive Strength(MPa) Tensile Strength(MPa) 2.94 (Yield (Yield Stress ) stress)

6 2.5 Interaction properties and Rayleigh damping The interacting surfaces between end surface of superstructure and face of parapet wall was determined as general contact surface algorithm with the friction coefficient of 0.45 and hard contact for pressure-over closure. Furthermore, an embedded constraint was used to constrain rebar element into solid element. In the numerical analysis, a damping model of Rayleigh type is used with the constant damping of Eigenvalue analysis The eigenvalue analysis was carried out in order to investigate the effect of seismic isolation rubber on the natural periods ofthe bridge.the natural periods and the effective mass ratio of each predominant mode were investigated in order to understand the fundamental dynamic characteristics of the structure. The maximum effective mass ratios in X, Y and Z directions imply the order of the predominant natural period. 2.7 Seismic response reduction measurement In order to improve the seismic performance of structures, the seismic isolation and energy dissipating systems are frequently used. These techniques are required to reduce the seismic forces by changing the stiffness and/or damping in the structures, whereas conventional seismic design is required for an additional strength and ductility to resist seismic forces [10]. In addition, the research and development works on these devices are being developed extensively. In this study, one layer and double layer of seismic isolation rubber have been placed at base of the pier in order to perform the analytical model in reducing the collisionbetween parapet wall and girder, as shown in Fig. 6. Rubber bearing was modeled by bilinear element in Figure 7 with the bearing stiffness of K 1 and K 2 weree calculated by the following equation. K = 6 K (1) K 2 = F Q ub e d (2) wheref is the maximum shear force (kn), Q d is calculated from the yield load and ub e is effective design displacement of the seismic isolation bearing (m). The stiffness of seismic isolation rubber was set to be K 1 = 2.27 x 10 4 kn/m 2 and K 2 = 0.35 x 10 4 kn/m 2 with Q y = kn. (a) 1 layer (R-1) (b) 2 layer (R-2) Figure 6. Analytical model of seismic isolation pier Figure 7. Bilinear model 84

7 III. RESULTS AND DISCUSSIONS 3.1 Modal analysis Tables 4 and 5 summarizes the natural frequencies, the natural periods and the effective mass ratios of each predominant mode of the bridge without seismic isolation rubberand one layer of seismic isolation rubber (R-0 and R-1 model), then two layer of seismic isolation rubber (R-2), respectively. Table 4. Eigenvalue results for R-0 and R-1 model Order R-0 model R-1 model of Effective Mass Ratio (%) T Effective Mass Ratio (%) f (Hz) T (sec) f (Hz) Periods X Y Z (sec) X Y Z Table 5. Eigenvalue results for R-2 model Order R-2 model of Effective Mass Ratio f (Hz) T (sec) (%) Periods X Y Z

8 (a) 1 st mode (b) 3 rd mode (c) 4 th mode Figure 7. Predominant mode of R-0 model (a) 1 st mode (b) 3 rd mode (c) 4 th mode Figure 8. Predominant mode of R-1 model (a) 1 st mode (b) 3 rd mode (c) 5 th mode Figure 9. Predominant mode of R-2 model The predominant Eigen modes deflecting in the longitudinal, vertical and transverse direction of bridge are shown in Figs According to these figures, it can be seen that seismic isolation rubber has a capability in reducing the frequency of bridge. R-0 model is possible to vibrate sympathetically at the 1 st mode in longitudinal direction, the 3 rd mode in in-plane direction and the 4 th mode in transverse direction, similar to R-1 model. However, installing of seismic isolation rubber in two layers leads the bridge to vibrate sympathetically in transverse direction at the 5 th mode, a slightly changed comparing to other models. 86

9 3.2 Response stress of the parapet wall Comparison result between the maximum response stressesat base of parapet wall(a1)for bridge with seismic isolation rubber ber and wing wall structure as parametric in different input ground motion are shown in Figs. 10(a)-10(f). R-0, R-1 and R-2 denote as the bridge without, with one layer and two layers of seismic isolation rubber, respectively. In addition, the response stresses of parapet wall (A2) are shown in Figs. 11(a)-11(f). W denotes the wing wall which is constructed in both sides of parapet wall. From these figures, it can be seen that input ground acceleration of L2T2G1 lead the structure to vibrate horizontally. It tend to move toward right direction and the maximum response occur in A2, with the exception of bridge in 10 cm of gap with L2T2G No collision occurs when the response stress is zero. Input ground acceleration of L2T1G1-2 2 and L2T1G1-3 cause the bridge to vibrate continuously in horizontal direction. Installing of the wing wall reduce the maximum response stress of parapet wall at a maximum percentage of 65%, as shown in Fig. 11(c). Different input ground motion lead the different ferent effect on the behavior of parapet wall. As an example is the input of L2T2G1-1 1 in bridge with 10 cm of gap, the response stress increase from 6.4 MPa to 39.7 MPa. In general,installing of the wing wall will decrease the response stress of parapet wall. Most of the results show the tendency of large response stress at the smallest gap of 10 cm, which is possibly due to increasing number of collision. On the other hand, gap does not give a significant effect on reducing the response stress in most cases of bridge analyses, as the exception of increasing gap from 10 cm to 20 cm from bridge without seismic isolation rubber. (a) L2T1G1-1 (b) L2T1G1-2 (c) L2T1G1-3 (d) L2T2G1-1 87

10 (e) L2T2G1-2 (f) L2T2G1-3 Figure 10. Maximum response stress at base of parapet wall in A2 (a) L2T1G1-1 (b) L2T1G1-2 (c) L2T1G1-3 (d) L2T2G1-1 (e) L2T2G1-2 (f) L2T2G1-3 Figure 11. Maximum response stress at base of parapet wall in A1 88

11 In analysis of bridge with one layer and two layers of seismic isolation rubber, the response stresses due to collision between girder and parapet wall reduced at a range up to 76% at the smallest gap of 10 cm.increasing gap from 10 cm to 50 cm raise the maximum response stress of parapet wall in general.however, in comparison between both layers, two layers seismic isolation rubber does not give a significant reduction effect on parapet wall. From these results, it was found installing of the wing wall or seismic isolation rubber on pier is one of an effective way to diminish the response stress of parapet wall on bridge. 3.3 Horizontal displacement of parapet wall Fig. 12 shows the maximum horizontal displacement at the top of parapet wall with the input seismic ground acceleration of L2T2G1. From this figure, it can be seen that the displacement of parapet wall in A1 positionis smaller than A2 position. Increasing the gap in bridge without seismic isolation rubber will diminish the displacement of the parapet wall. The displacement behavior of parapet wall in left and right side without and with consideration of the wing wall are shown in Fig. 13 and Fig. 14. The deformation scale is 10 times the real deformation. (a) A1 position (b) A2 position Figure 12. The maximum horizontal displacement at top of parapet wall in L2T1G1-2 (a) A1 position (b) A2 position Figure 13. Displacement behavior of parapet wall for bridge with L2T1G1-1-R0-10cm 89

12 (a) Left side (b) Right side Figure 14.Displacement behavior of parapet wall with L2T1G1-3-R0W-10cm From these figures, it can be described that wing wall part contributes greatly to the horizontal resistance of abutment against load. During the collision, a large displacement amount towards the central parapet occurs. 3.4 Cracking distribution of parapet wall The cracking distribution of parapet wall due to tensile stress for parapet without and with consideration of the wing wall are shown in Figs , respectively. Cracking starts when it has a positive value, depicted as initial cracking. Then, it propagates up to the maximum value of 0.9. The area of no cracking and maximum cracking are figured out as dark blue regions and white regions, respectively. From these results, it can be explained that cracking propagates from center part through its width in parapet wall. This propagation leads cracking in edge section between parapet wall and wing wall. No-cracking Initial cracking Final cracking (a) Initial cracking at 1.15 sec (b) Final cracking at sec Figure 15. Contour plot of tensile damage in parapet wall for L2T2G1-1-R0-10 No-cracking Initial cracking Final cracking (a) Initial cracking at sec (b) Final cracking at sec (c) Figure 16. Contour plot of tensile damage in parapet wall for L2T1G1-3-R0W-10 90

13 3.5 Effect of gap on number of collision Effect of the increasing gap to the number of collision between end of girder and parapet wall in bridge without wing wall are shown in Figs. 17(a)-17(e). Results are compared between response stress of parapet wall and end of girder. From these figures, it can be described that increasing the gap will decrease the number of collision. On the other hand, reverse effect occur when installing of seismic isolation rubber, as shown in Figs. 18(a)-18(e). In addition, seismic isolation rubber causes the bridge with input of L2T1G1 to sway in one direction with an evidence of increasing number of stress continuously after the final impact. (a) Gap 10 cm (b) Gap 20 cm (c) Gap 30 cm (c) Gap 40 cm (e) Gap 50 cm Figure 17. Response stress on bridge of L2T1G1-1-R0 91

14 (a) Gap 10 cm (b) Gap 20 cm (c) Gap 30 cm (c) Gap 40 cm (d) Gap 50 cm Figure 18. Response stress on bridge of L2T1G1-1-R1 IV. CONCLUSIONS The seismic behavior of concrete girder bridges subjected to strong ground motions considering the effect of collision, base-isolated pier and wing wall were investigated by dynamic response analysis. Numerical studies were carried out in bridges with the parameters of gap, seismic isolation rubber and wing wall. Two types of Level 2 seismic ground motions according to JSHB seismic waves were simulated and discussed. The conclusions of this study are summarized as following. 1) Installation of the wing wall in parapet had a capability in reducing the maximum response stress of parapet wall. In addition, it contributed greatly to the horizontal resistance of abutment against load. 92

15 2) Adopting of seismic isolation rubber on pier structure had a great effect on the response behavior of bridge. In the smallest gap of 10 cm, it diminished the response stress of abutment up to 76%. Generally, increasing the gap was also increase the maximum response stress of parapet wall. 3) In comparison between installation of one layer and two layers of seismic isolation rubber, the effect of reducing the response stress due to collision was obtained. However, considering to the cost of structure, sufficient reduction effect was found in behavior of one layer seismic isolation rubber. 4) Increasing of gap from 10 to 50 cm in bridge with and without installation of wing wall decreased the number of collisionon parapet wall. On the other hand, reverse effect occurred in bridge with seismic isolation rubber. 5) Initial cracking was found at the bottom of parapet wall and spread through the parapet width. Installation of the wing wall caused cracking at the edges of parapet wall which was connected to the wing wall. 6) Further study is necessary in order to investigate the effect of soil pressure during earthquake on the behavior of bridge. ACKNOWLEDGEMENT The first author acknowledges DIKTI (Directorate General of Higher Education) in Indonesia as the financial supporter of the scholarship and University of Brawijaya as the home university. Their support in completing the doctoral study in Kumamoto University is gratefully appreciated. REFERENCES 1. Japan Road Association, Specifications for Highway Bridges Part V: Seismic Design, H. Tamai and Y. Sonoda, A numerical study on the dynamic behavior of concrete bridges by pounding effect, 8 th International Conference on Shock & Impact Loads on Structures, Adelaide, Australia, T. Hamamoto, T. Moriyama and T. Yamao, The effect of cost performance on seismic design method allowing the pounding of pc bridge girders, 10 th International Conference on Shock & Impact Loads on Structures, Singapore, Dassault Systems Simulia Corp., ABAQUS/CAE User s Manual 6.11, Providence, RI, USA, A. Ahmed, Modeling of a reinforced concrete beam subjected to impact vibration using ABAQUS, International Journal of Civil and Structural Engineering, 4 (3), 2014, A.R. Mohamed, M.S. Shoukry and J.M. Saeed, Prediction of the behavior of reinforced concrete deep beams with web openings using the finite element method, Alexandria Engineering Journal, 53, 2014, H. Sinaei, M. Shariati, A.H. Abna, M. Aghaei, and A. Shariati, Evaluation of reinforced concrete beam behavior using finite element analysis by ABAQUS, Scientific Research and Essays, 7(21), 2012, S.N. Mokhatar and R. Abdullah, Computational analysis of reinforced concrete slabs subjected to impact loads, International Journal of Integrated Engineering, 4(2), 2012, D. Setyowulan, T. Hamamoto and T. Yamao, Elasto-plastic behavior of 3-dimensional reinforced concrete abutments considering the effect of the wing wall, International Journal of Civil Engineering and Technology (IJCIET), 5(11), 2014, N. Torunbalci, Seismic isolation and energy dissipating systems in earthquake resistant design, 13 th World Conference on Earthquake Engineering, Canada,