Rocking effect on seismic response of a multi-story traditional timber pagoda model

Characterized by discontinuous vertical elements and high aspect ratios, multi-story traditional timber pagodas in Southeast Asia have been of interest to many researchers. Combined with shake table tests on a one-fifth scaled seven-story traditional timber pagoda, this paper investigates the effect of rocking on the seismic behavior of multi-story traditional timber pagodas. Firstly, to describe the rocking behavior of timber columns, a modified empirical formula is proposed and verified by experiments. Secondly, considering discontinuous columns in multi-story traditional timber pagodas as rocking elements, mechanical properties of such columns under lateral loading are determined by use of the proposed formula. Thirdly, a simplified numerical model is developed in OpenSees, with which time history analyses are conducted to simulate the dynamic responses of the scaled timber pagoda subjected to earthquake excitations of various intensities (0.2 g, 0.44 g and 0.8 g). Finally, the numerical and shake-table experimental results are compared and discussed. It is found that the numerical simulation captures efficiently and with high accuracy most of the dynamic response characteristics along the structural height under each excitation intensity, including acceleration responses, displacement peaks and major natural frequencies. Major conclusion of this study is that the rocking-based numerical simulation can effectively predict the dynamic responses of the pagoda model under high intensity earthquakes. The proposed simulation method can be conveniently utilized to provide reasonable references for design or strengthening similar structures.