两点支承平面结构多点输入随机地震响应分析

推导双支座双质点简化模型多点输入地震响应功率谱密度函数解析式,从中分离出多点效应项,借此研究行波效应和部分相干效应等多点输入效应对大跨结构随机地震响应的影响.并以一门式桁架结构为例,检验由简化模型得到结果的实用性.研究结果表明:行波效应和部分相干效应均增大结构拟静力响应;相对动力响应受行波效应影响呈三角函数式波动,极值点分布由自振频率与行波频率的比值确定,极值点特性由振型特性与地震动方向共同确定;部分相干效应减小相对动力响应随行波频率的变化幅度,但不改变相对动力响应的极值点分布规律.对于实际工程而言,选取不同的视波速得到的结构响应差别很大,应使用可靠视波速或采用多个可能视波速试算才能保证计算结果的可靠性;部分相干效应的影响相对较小,特别是当结构跨度较小时,几乎不受部分相干效应的影响.

Analysis on Random Seismic Response of Two Supporting Plane Structures under Multi support Excitation

The variable of multi support excitation effect, which is extracted from the analytical formulae of the power spectrum density function (PSDF) of seismic response of a 2 mass with 2 support simplified system, was proposed to study the variation of the random seismic response due to the wave passage effect and incoherence effect. And a numerical example of a gate type truss structure was given to validate the practicability of the results gained from the simplified system. It is shown that the quasi static response will increase while considering the wave passage effect or incoherence effect; the relative dynamic response fluctuates with the increase of wave passage frequency, and the extreme point''s distribution is determined by the ratio of natural vibration frequency to wave passage frequency; and the incoherence effect will not change the extreme points'' distribution, but reduce the fluctuation amplitude. For actual structures, more wave velocities are proposed to be employed to obtain reliable results, since they have a strong influence on the seismic response. The incoherence effect has little influence on the actual structures, especially when the structure''s span is small.