视波速确定方法与行波效应研究

通过对地震波在单一土层和不同土层之间传播规律的研究，提出基于岩土层剪切波速的视波速计算方法，并给出多土层视波速简化计算公式，便于工程应用。对于均质土层，地面某点的视波速仅与该点震源深度、震中距和土层的剪切波速有关，视波速恒大于剪切波速。采用结构中点的视波速取代根据其两端点得到的视波速，可以避免结构各方向长度不同的影响，计算简便，误差可以忽略不计。在震源深度范围内，地壳厚度通常远大于覆盖层厚度，多土层的等效剪切波速与震源所在岩层剪切波速较为接近，场地类别对视波速的影响较小。算例结果表明，文中给出的多土层视波速简化计算方法，与视波速方程数值解的误差一般在5%以内。根据95%构件内力影响系数的最大值确定地震行波效应的放大系数，可以避免由于构件内力过小引起行波效应异常增大。厦门新机场分析结果表明，考虑多点激励地震效应后，航站楼结构底部总剪力变化很小；虽然框架柱、支承屋盖钢管柱和大跨度屋盖杆件内力的平均值减小，但部分构件内力可增大约5%~10%。

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%.