A shake table test for the rotation response of rigid bodies under seismic excitation

In 2008 Wenchuan earthquake, an interesting torsion phenomenon attracts our attention: Most of the stone statues, which were placed upon the banisters of one zigzag bridge in Taibai Park, Jiangyou City, Sichuan Province, rotated an angle from their original location with little translation displacements. To simulate and further study this phenomenon, a group of stone statue models with different asymmetric characteristics were made, and then they were arranged in different location and direction on the shake table to do shake tests. The results show that: ① The torsional phenomena of the statue models appeared when input 3D accelerations from the shake table, and the acceleration amplitudes are 1.5 times of the original seismic records. Also, the phenomena were similar to those in the Taibai Park in Wenchuan earthquake. However, when the input accelerations were only in two horizontal directions, the torsional phenomena would not appear even when the amplitude was large enough. ② The torsional phenomena of the stone statue models showed different modes with different model asymmetric characteristics and different acceleration input angles. ③ The most significant factor that causes the torsional phenomena is the vertical seismic input. The statue rotation did not occur without it. So for this case, vertical ground motion is crucial and cannot be ignored.