Seismic assessment and fragility analysis of traditional Chinese timber frame building considering degraded connections

This paper studies the influence of degraded connections on dynamic characteristics, seismic response, and seismic fragility behaviors of traditional Chinese timber-framed buildings. Numerical models are developed based on the extended distinct element method, and calibrated with 1:3.52 scaled shake-table test data. The influence of fracture and wood aging on the performance of both mortise-tenon joints and Dougong brackets connections is discussed. A set of 20 ground motion records are selected for an incremental dynamic analysis, seismic behaviors, and fragility assessment. Results indicate that considering 0.75 times and 0.85 times degradation of mortise-tenon joints, natural frequencies are reduced by 8%, and 4%, respectively, and 4%, and 2% for Dougong brackets connections, respectively. The maximum acceleration response is reduced at most by 1.8% and 0.9%, respectively, and the maximum relative displacement is promoted by 7.3% and 5.3%, respectively. In addition, for a peak inter-structural layer drift of 1/442, 1/148, and 1/48, seismic intensities corresponding to median probabilities of exceedance of the structure with 0.75 times degraded performance of mortise-tenon joints are reduced by 32%, 16%, and 9%, respectively, and 14%, 6%, and 3% for Dougong bracket connections.