Shake table experiment on circular reinforced concrete bridge column under multidirectional seismic excitation

Since the 1971 San Fernando, CA, earthquake, a significant amount of research has been conducted on the ductility capacity of reinforced concrete bridge columns, resulting in significant advances in the seismic design of bridges. Since most tests have been done in static or quasistatic conditions and unidirectional loading conditions, however, no method that properly evaluates the effect of multidirectional dynamic loading has been developed, and design recommendations on this effect are still limited. It is essential to evaluate the effect of multidirectional loading on the dynamic response and seismic performance of reinforced concrete bridge columns in order to develop more advanced and reliable design procedures. Research on the dynamic behavior of reinforced concrete bridge columns under multidirectional loading is still limited due to the limitation of capacity of research facilities. Mahin and Hachem conducted a series of shake table tests of circular reinforced concrete bridge columns. The effect of multidirectional loading was investigated for 406 mm-circular columns. Nishida and Unjoh conducted a series of shake table tests for three types of cross sections, circular (600 mm in diameter), square (600 x 600 mm) and rectangular (450 x 800 mm), under a near field ground motion, and then conducted dynamic analyses to investigate the effect of bilateral loading. Sakai and Mahin conducted shake table tests of a circular reinforced concrete bridge column as a part of a research project to develop a new method that mitigates post-earthquake residual displacements. Although these tests provide valuable data for development of advanced analytical procedures and findings to be considered in seismic design on the multidirectional dynamic loading effects, most columns were tested under a near field ground motion, which has a few dominant pulses, and the dynamic behavior under repetition of strong pulses has not well been investigated. In the study presented here, the dynamic response of a circular reinforced concrete bridge column specimen under a repetitive strong shaking is investigated through shaking table tests. Accuracy of an analytical model using a fiber element is evaluated with the test results, and then the effect of multidirectional seismic excitation is analytically investigated.