STUDY ON APPARENT WAVE VELOCITY CALCULATION METHOD AND ON TRAVELLING WAVE EFFECT

By studying the propagation pattern of seismic waves in a single soil layer and between different soil layers, a calculation method for apparent wave velocity based on the shear wave velocity of rock/soil layers was proposed. A simplified calculation formula of the apparent wave velocity for multiple soil layers was also developed for the engineering application convenience. For a homogeneous soil layer, the apparent wave velocity at a certain point on the ground is only related to the focal depth, to epicenter distance and to shear wave velocity, then the apparent wave velocity is always greater than the shear wave velocity. Using the apparent wave velocity at the midpoint of the structure instead of the apparent wave velocity obtained at its two ends can avoid the influence of the different lengths of the structure in all directions, the calculation is simple and the error can be ignored. In the depth range of the source, the thickness of Earth Crust is usually much larger than that of the overburden layer. The equivalent shear-wave velocity of multiple soil layers is close to the shear wave velocity of the rock layer where the source is located, and the site category has little effect on the apparent wave velocity. The results of the calculation examples show that the error of the simplified calculation method for the apparent wave velocity of multiple soil layers is generally within 5% of the numerical solution of the apparent wave velocity equation. According to the maximum value of internal force effect coefficients of 95% components to determine the amplification factor of the seismic traveling wave effect can avoid the abnormal increase of the traveling wave effect caused by the internal force of a little components being too small. The analytical results of Xiamen New Airport show that: after considering the multi-support seismic excitation, the change of the total shear force at the terminal structure bottom is very small; although the mean value of internal forces for frame columns, for steel pipe columns supporting roof and for long-span roof members decrease, the internal forces of some structural members can increase about 5%~10%.