SHAKING TABLE TESTS OF CFST REINFORCED CONCRETE PIER WITH HOLLOW BOX SECTION

Based on the prototype of the No.11 pier of Labajin Bridge, the shaking table tests was carried out for a CFST reinforced concrete pier with a hollow box section (CFSTRC-HBS pier for short) and with a geometric scale of 1∶9.43. Combined with the nonlinear finite element analysis of a spatial member system, the seismic response characteristics and failure mechanism of the CFSTRC-HBS pier under strong earthquakes were analyzed. The results showed that: under the action of E2-level earthquake, most of the plastic hinge sections at the bottom of the scaled model and prototype piers were under compression, and there were no cracks on the structural surface, i.e., the structures were in an elastic working state. The seismic response of the CFSTRC-HBS pier was significantly affected by the characteristics of ground motion. Among the nine classical seismic waves (PGA=0.05 g), the acceleration and displacement response of the pier top under the action of the Wenchuan-NS wave reached the maximum, which were 1.8 times and 5.4 times of the minimum seismic response, respectively. With the intensity of the Wenchuan-NS wave was increasing at an increment of 0.05 g, the acceleration response and displacement response of the pier top increased linearly and the acceleration dynamic-amplification factor maintained at about 6. The finite element results based on fiber beam-column elements were in a good agreement with the experimental results. The further nonlinear time history analysis showed that: when PGA was 0.30 g, the encasing concrete at the tension side of the potential plastic hinge area at the bottom of the pier cracked. When PGA was 0.75 g, the steel tube yielded, but the concrete did not crush at the compression side. Under the bilateral seismic actions, the peak displacement response of the pier top and the maximum internal force of the pier bottom increased by about 6% and about 4%, respectively, compared with the results of unilateral seismic action. It shows that the simultaneous action of bilateral earthquakes has little effect on the seismic response of CFSTRC-HBS piers. The horizontal ground motions in the longitudinal and horizontal directions can be input separately when analyzing the seismic response of CFSTRC-HBS piers.