地震动输入方法研究

DISCUSSION ON EARTHQUAKE INPUT METHOD

为探讨直接求解法、相对运动法、大质量法和等效荷载法四种地震动输入方法的差别,对四种地震动输入方法的机理进行了分析,结果表明:直接求解法是通过直接求解结构在多点激励作用下的动力学平衡方程来获得结构响应的方法;相对运动法将结构响应分成(拟)静力响应和动力响应,可用于一致激励下结构的线性和非线性反应分析;大质量法是一种简化计算方法;等效荷载法将地面运动用等效力代替,只能用于一致激励情况。给出的线性与非线性分析数值算例也验证了一致激励情况下,在不考虑结构响应的时滞效应,以及结构阻尼处于常用阻尼(阻尼比0.02―0.05)范围内时,除在非线性时间历程分析的中后期,等效荷载法与直接求解法、大质量法计算的结构响应有一定的偏差外,上述各种方法计算的结构响应保持较好的一致性。考虑到一般的建筑结构在罕遇地震下并不会全面进入塑性,三种方法的计算结果应该都是比较可靠的。

To discuss the difference among the direct solving method, the relative motion method, the large mass method and the equivalent load method, the mechanisms of four earthquake input methods are analyzed. The results show that the direct solving method is a method through which the dynamic equilibrium equation can be solved directly under multiple-support seismic excitations to get the response of the structure; the relative motion method, which divides the structural response into a dynamic response component and a pseudo-static response component, can be used to analyze the linear and nonlinear response of the structure under uniform excitations; the large mass method is a simplified calculation method; the equivalent load method, which replaces ground motion by equivalent load, can only be used under uniform excitations. The linear and nonlinear numerical examples also illustrate that, under uniform excitations for the engineering structures with the damping factor from 0.02 to 0.05 and without consideration the time delay phenomena, the structural responses calculated by the direct solving method, the large mass method, the equivalent load method agree well with each other, except those calculated by the equivalent load method and the direct solving method as well as the large mass method exist a deflection in the middle and latter phase of the structural responses. Considering that the structures can not fully enter into plastic stage under rare earthquakes, the results calculated by them should be reliable.