Contents lists available at ScienceDirect Soil Dynamics and Earthquake Engineering journal homepage: www.elsevier.com/locate/soildyn Experimental study on relative displacement responses of bridge frames subjected to spatially varying ground motion and its mitigation using superelastic SMA restrainers Bipin Shrestha a, ⁎ , Li-Xiang He b , Hong Hao c , Kaiming Bi c , Wei-Xin Ren d a SMEC, Level 1, 243 Northbourne Avenue, Lyneham, Canberra, ACT 2602, Australia b Department of Civil Engineering, Central South University, Hunan, China c Centre for Infrastructural Monitoring and Protection, School of Civil and Mechanical Engineering, Curtin University, Kent Street, WA 6102, Australia d Department of Civil Engineering, Hefei University of Technology, Hefei, China ARTICLE INFO Keywords: Shake table testing Pounding Relative displacement Spatially varying ground motion SMA restrainers ABSTRACT Contemporary bridge codes recommend adjusting the fundamental frequencies of adjacent segments close to each other to mitigate relative displacement induced damages arising during the strong seismic events. Previous studies revealed that such recommendation leads to effective mitigation of damages on the bridge structures subjected to uniform ground motions. However, in an elongated bridge structure spatial variations of earthquake ground motions at different supports are inevitable which can result in larger relative displacements. This study presents experimental results from a large-scale (1/6) shake table testing of bridge models with two bridge frames having a total length of 16.67 m, subjected to spatially varying ground motions. Experiments were also carried out with bridge model with superelastic Shape Memory Alloy (SMA) restrainers to evaluate its effec- tiveness on mitigating bridge responses. It is revealed that even the adjacent bridge frames with fundamental frequencies close to each other are susceptible to the localized damages at the joints due to poundings, which could lead to delayed access to the affected sites after an earthquake. Superelastic SMA restrainers could ef- fectively reduce the opening relative displacement and pounding intensity. Moreover, owing to its superelastic behaviour the restrainers would not require replacement even after strong seismic events. Finally, numerical models of the bridge were developed and parametric studies were performed to comprehend the results of the experiment. 1. Introduction During major earthquakes, adjacent segments of multiple-span bridges could suffer damages resulting from out-of-phase vibrations of the adjacent bridge segments. The out-of-phase vibrations result in two major problems. Firstly, unseating failure of bridge span can occur if opening relative displacements between the bridge segments exceed the available seat widths. Many cases of the bridge collapse that occurred in recent earthquakes were attributed to this phenomenon [1–3]. Sec- ondly, pounding of the adjacent segments occurs if the closing relative displacements exceed the expansion joint width. Poundings of the ad- jacent bridge segments have been observed in almost all major earth- quakes, resulting in localized damages and crushing of concrete at impacting locations. Moreover, pounding between adjacent bridge segments could result in the transfer of momentum that leads to a larger relative joint opening displacement at expansion joints thus increasing the risk of unseating damage of bridge span [4]. The out-of-phase vibrations between the segments of an extended bridge structure can result from the differences in the dynamic char- acteristics of these segments and the variation of earthquake ground motions along the length of the bridge. Present design codes suggest adjusting the fundamental frequencies of adjacent structures to mitigate relative displacement induced damages in bridges. However, adjusting the fundamental frequencies of adjacent structures only is not sufficient to prevent damages at bridge joints owing to the inevitable spatial variation of earthquake ground motions. Previous studies revealed that many reasons can result in the spatial variability of seismic ground motions, e.g. the wave passage effect owing to the different arrival times of seismic waves at different locations; the coherency loss effect due to seismic waves scattering in the heterogeneous medium of the ground; and the site amplification effect owing to different local soil properties. Many earlier studies have considered only the wave passage https://doi.org/10.1016/j.soildyn.2018.03.005 Received 27 September 2017; Received in revised form 18 January 2018; Accepted 4 March 2018 ⁎ Corresponding author. E-mail addresses: bipinsh01@gmail.com, bipin.shrestha@smec.com (B. Shrestha). Soil Dynamics and Earthquake Engineering 109 (2018) 76–88 0267-7261/ © 2018 Elsevier Ltd. All rights reserved. T