Analysis of Rocking Behavior of Tang-Song Timber Frames under Pulse-Type Excitations

This paper investigates the rocking behavior of two free-standing columns capped with a freely supported superstructure in an effort to explain the seismic stability of Tang-Song timber frames subjected to pulse-type excitations. The geometric characteristics of the column determine the acceleration amplitude needed to create uplift of the rocking frame, which also affect the loss of energy during impact along with the mass ratio of the superstructure to the column. Two distinct rocking modes are analyzed according to whether the frame can be limited by the tenon-mortise joint. The expression that yields the minimum acceleration required to overturn the frame is derived within the limits of the linear approximation of the governing equation of motion. Different safety and overturning regions plotted on the stability diagrams indicates that the partially joint limitation may weaken the seismic behavior. The entirely limited frame will rock within the fixed amplitude caused by the joint gap and never topple down. Probability analysis results of the entirely limited frame suggest that a great majority of this type of traditional timber structures have excellent seismic capacity to resist the horizontal excitation.