Shake Table Tests of Tall-Pier Bridges to Evaluate Seismic Performance

Abstract

More than 4% of the bridges in mountainous areas of Southwest China are constructed with piers having a height of over 4 m. Such piers are characterized by large structural flexibility and distributed mass. To investigate the effects of higher modes on the seismic performance of this class of bridges, shake table tests on two 1/7-scale, tall-pier models were conducted at Tongji University, Shanghai. This paper describes the design, instrumentation, and loading protocols for the tests and discusses and compares the results. Due to the higher-mode effects, the curvature at the pier base and displacement at the pier top of were found to be weakly correlated, indicating that displacement is not a reliable damage measure for tall piers. Moreover, results indicated that the contribution of higher modes can lead to the formation of an additional plastic region at midheight in the piers. However, current seismic design code guidelines are for short to medium-height piers, where the midheight region of piers is assumed to respond elastically; code guidelines are not provided for tall piers. This paper explores the effect of higher modes on the seismic performance of bridges with tall piers and suggests two methods to improve the seismic performance: (1) eliminating the midheight plastic response by including more longitudinal steel, and (2) using more confinement in the midheight region to improve pier ductility and prevent shear failure.