REFLECTION AND TRANSMISSION COEFFICIENTS OF THE SIMPLIFIED WAVE PROPAGATION METHOD FOR PREDICTING DYNAMIC RESPONSES OF STRUCTURES SUBJECTED TO IMPULSE-TYPE VERTICAL EXCITATIONS

Some structures may be subjected to a strong impulse effect under a near-fault vertical seismic wave with various frequency components and large propagation speed. When the wave propagation method is used to analyze the dynamic responses of multi-degree-of-freedom (MDOF) systems under impulse-type longitudinal excitations, the computational process is generally sophisticated and not easy to converge. It is also not desirable to apply vibration mechanics to reflect the impulse effect and depict stress wave-induced damage since it cannot well reflect the time delay and reflection of stress waves propagate through floors. The wave propagation method has been combined with vibration mechanics herein to derive the reflection and transmission coefficients of longitudinal wave propagates through simplified lumped masses at floors in which the damping effect is considered. Based on this, a parametric study was carried out to investigate the effects of the damping ratio, axial stiffness ratio and mass ratio on these coefficients. A further discussion on the possible application of the coefficients to studying the interaction between soil and superstructures was performed as well. The results from this paper indicate that it is very necessary to consider the damping ratio in the reflection and transmission coefficients. The relationship curves between amplitude and frequency curves have shown a significant high-frequency filter effect and a strong dependence on axial stiffness and mass ratio. The investigation could form the basis of using the simplified wave propagation method to evaluate the dynamic responses of MDOFs excited by the impulse-type vertical component of near-fault strong ground motions.