Behavior of partially concrete-filled steel tube bridge piers under bi-directional seismic excitations

• We conduct bidirectional pseudo-dynamic tests on PCFST bridge piers.
• Adequate concrete fill can effectively improve seismic behavior of PCFST piers.
• Low concrete fill may lead to severe damage or collapse during earthquakes.
• Bidirectional loadings deteriorate deformation capacity of piers considerably.
• A more reasonable bi-directional seismic verification method is proposed.

During the past decades, amounts of research efforts have been concentrated to investigate basic characteristics of the seismic response of steel bridge piers by cyclic bi-directional loading tests or finite element analysis. However, dynamic test results on partially concrete-filled steel tube (PCFST) bridge piers under coupled ground motions in two horizontal directions are insufficient. To investigate the behavior of PCFST bridge piers under bi-directional seismic excitations, a series of cyclic static loading tests and single- and bi-directional hybrid (pseudo-dynamic) loading tests for circular-section test specimens with three different concrete-filled ratios were performed in this study. The failure patterns were observed after the tests. The experimental results showed that the restoring force of PCFST bridge piers obtained in bi-directional loading tests was almost the same as that obtained in single-directional loading tests. However, deformation capacity deteriorated considerably when subjected to bi-directional dynamic loadings. This study also shows that the seismic behavior of PCFST bridge piers can be effectively improved if the concrete fill height is significantly increased.