Modeling Hysteretic Behavior of Lateral Load-Resisting Elements in Traditional Chinese Timber Structures

Dou-gong connections and mortise-tenon jointed traditional timber frames are widely used in traditional Chinese timber structures to resist lateral loads. Such elements exhibit strong nonlinearity in unloading routes, especially at drifts beyond the peak load. This paper proposes a multifunctional model for the hysteretic behavior of dou-gong connections and mortise-tenon jointed timber frames. The proposed model is capable of capturing the asymmetric envelopes in opposite loading directions via two sets of ten adjustable parameters and utilizes Bézier curves for the unloading routes and linear pinching routes via nine parameters. The model validity was discussed in comparison with two commonly used models—the SAWS and the Pinching4 models—based on the reversed cyclic test results of typical traditional Chinese dou-gong connections and mortise-tenon jointed timber frames. The use of the Bézier curves and two different unloading patterns in the proposed model was found to be more reasonable than the piecewise linear unloading routes used in the SAWS and Pinching4 models. The proposed model agrees better with the test results in both the load-displacement hysteretic curves and the energy dissipation. The case study on the seismic fragility of traditional Chinese mortise-tenon jointed timber frames confirms the computation stability of the proposed model by the smooth hysteretic curves established based on the seismic accelerations and the resulting displacements.