Effects of reinforcement ratio on seismic performance of hypothetical stations determined by full-scale central column tests

The reinforcement ratio of central column member has remarkable effect on the seismic behaviour of double-box stations. To investigate the effects of reinforcement ratio on seismic performance of hypothetical stations, hybrid simulations and quasi-static cyclic tests on five full-scale column specimens of various reinforcement ratios were presented in this paper. The five column specimens are comprised of a reference specimen and four specimens with the reduction in either longitudinal or transverse reinforcements. In the hybrid simulations, the physical specimen consisted of one central column, while the rest of the soil-structure system were modelled numerically using the OpenSEES software. Seismic loading to the columns was applied via displacement-controlled actuators to illustrate the drift demands of the station during hybrid simulations at three levels of ground motions. The hybrid simulation results showed that the column specimen with minimum longitudinal reinforcement ratio entered the yielding stage and the other four specimens were in the cracking stage. Furthermore, the quasi-static cyclic tests were carried out to investigate the strength and deformation capacity of tested columns. Results from both hybrid seismic tests and quasi-static cyclic tests indicate that central columns, with a high shear span-to-depth ratio and light transverse reinforcement, are prone to suffer brittle flexural-shear coupled failure. On the other hand, the columns of sufficient transverse reinforcement are likely to experience flexural failure. The safety margins between the seismic drift response and ultimate deformation capacity indicate that the drift ratio threshold of subway stations used by current code provisions is conservative for flexure-dominate columns.