Energy-based estimation of ductility demand of slip-hysteretic timber house structures subjected to sequential earthquakes

Under earthquake loading, timber house building exhibits hysteresis with a significant pinching effect characterized by degraded stiffness and reduced energy dissipation capacity. Such a phenomenon implies that timber structures may become critical when subjected to sequential earthquake excitations. Both the seismic input energy and the ductility of structures are essential indexes for quantifying the damage level of structures. For constructing a relationship between the two indexes, numerical analysis was performed on a single-degree-of-freedom structure represented by a pinching hysteretic model. The repeated sequence and the as-recorded sequence were used as the input earthquake sequences. It was shown that sequential earthquakes significantly increase the ductility demand in a pinching-hysteretic structure. The ductility ratio resulting from the two sequential earthquakes can be modeled as a power function of the input energy ratio, and the relation can apply to both types of sequence models. Numerical results were verified by a shaking table test previously performed on a typical traditional timber house. The result suggested that the effect of sequential earthquakes and the increased ductility demand should be accounted for in estimating the seismic performance of traditional timber buildings.