Effects of orientation angle of spectrum-compatible bidirectional ground motions on nonlinear seismic response of bridge piers considering progressive damage process

The Orientation Angle (OA) of bi-directional ground motions affects the nonlinear response of structures. In this study, a suite of RotD100 spectrum-compatible bi-directional ground motions is generated, such that OA remains constant regardless of the natural period and is compared with another suite with non-constant OA. Idealized single-column steel bridge piers involving a progressive damage process are utilized to investigate the effect of OA on nonlinear seismic response. Incremental Dynamic Analysis (IDA) is conducted with the two suites of bi-directional ground motions applied to the piers through 360° at an angle increment of 9°. It is shown that the difference in seismic demanding between the two suites of bidirectional ground motions becomes significant as Peak Ground Acceleration (PGA) increases. The seismic demand of bi-directional ground motions with constant OA is severer when the piers are subjected to strong earthquakes (i.e., PGA is high). This sheds light on the importance of a reasonable suite of bi-directional ground motions in designing new bridges or retrofitting old bridges.