Modal Properties of a Model of a Chinese Pagoda

Abstract

China has been building wood frame pagodas since 200 ad during the Han Dynasty. A pagoda is essentially a multi-story tower, and each story is a separate building consisting of all structural components. This paper describes a series of shake table tests conducted on a one-fifth scale model of a seven-story pavilion-style wooden pagoda recently conducted at Tongji University in Shanghai, China. The main purpose of these tests was to investigate the seismic performance of this model pagoda. The model of the pagoda was subjected to different levels of excitation simulating ground shaking generated by earthquakes. White noise excitation was also used to determine the dynamic characteristics of the structure. The results of the modal analyses conducted using the various datasets are presented and discussed in this paper. The parameters studied include modal frequencies, damping and modes shapes of the structure. The variation of these parameters with the increasing levels of ground excitation is investigated, and these are correlated to the nonlinear behaviour and damage observed during each test. A detailed analysis of the mode shapes of the structure indicates that a soft-story behaviour of the first floor of the structure is noticeable with increasing level of shaking. Considering that the pagoda’s connections using the Dou-gong style are made of wood only, the behaviour of the structure during extreme levels of excitation was excellent and very minor damage was observed. The mortise-tenon joints of the timber frame dissipated most of the seismic energy.