The investigation of multi-storied Japanese timber pagodas during earthquake events and the application of non-linear joints within virtual models

Abstract

This paper investigates the structural mechanisms contributing to the excellent performance of Japanese pagodas during earthquake events and applies them to modern multi-storeyed timber structure models. Horyu-ji Pagoda was used as a basis for the modelling of the pagoda structure.

It was discovered that there were six major mechanisms, these were; base isolation joints, sliding friction joints, rocking column joints, nuki joints, a balancing toy effect and the presence of a central pillar (shin-bashira). The first four unique joints were chosen to investigate further for practicality reasons, and they were added to a generic three-storied timber model. These models had different earthquake time histories applied to them and output data was collected using non-linear time history (NLTH) analysis. They key output data that was analysed was the acceleration, displacement and storey drift at each level of the different models. The energy dissipation within the models were also investigated. It was found that each of the unique joints had a certain strength and weakness in decreasing the effects of the earthquake on the structure, however when all of them were used together the best results were seen.

The combined mechanisms model had an average decrease of 43% in peak acceleration, 50% in average acceleration, 31% in peak displacement, 37% in peak storey drift, 65% in maximum internal energy and 81% in residual energy. The model had a 13% increase in peak displacement when considering horizontal loading due to wind. These differences were observed when comparing the combined mechanisms model to a generic timber model with joints that were all linear and moment resisting.