多点非均匀调制演变随机激励下结构地震的响应

针对大跨度结构在非均匀调制演变随机激励作用下，考虑行波效应时的非平衡随机地震响应问题，应用虚拟激励法进行了分析，由于虚拟激励法自动计及了参振振型的互相关项以及激励之间的互相关项，理论上是精确解，时变功率谱的计算采用精细逐步积分格式，使计算效率进一步得到提高。

SEISMIC RESPONSES OF STRUCTURES SUBJECTED TO NON-UNIFORMLY MODULATED DIFFERENTIAL EVOLUTIONARV RANDOM EXCITATIONS

Prestley's mathematical model of non-uniformly modulated evolutionary random pro- cess takes into account the non-stationary chaxacteristics not only of the excitation intensity, but also of the excitation frequency components. Therefore, it has been considered as physically rather reasonable in simulating general earthquake excitations for a long time. Unfortunately, as this model is expressed in terms of Riemann-Stielties Integration, the relevant computation is very difficult. So far, this model is still considered as unacceptable by practicing engineers even for single excitation problems. In order to simplify the computation, usually the non-stationary characteristics of the excitation frequency components is ignored, namely, the excitations are assumed to be uniformly modulated. In fact, the problem thus simplified is still rather difficult. In this paper, long span structures subjected to non-uniformly modulated differential evolutionary random seismic excitations are analyzed by means of the PEM (pseudo excitation method), an accurate and efficient way. By using this method, the wave passage effect is strictly dealt with, and the cross-correlation terms both between all participant modes and between ground excitations are accurately involved. This method is convenient because the non-stationary random excitations are transformed into deterministic excitations, and so ordinary step-by-step intergration methods such as Newmark or Wilson-0 schemes can be directly used. In this paper) the precise integration method is used, and so the computation efficiency has been further remarkbly raised. A numerical example about an earth-stone dam built in China is given. Its finite element model has about 3000 degrees of freedom and more than 100 ground joints. The results show that it is significant for structural components, which are sensitive to higher frequencies, to regard the excitations as non-uniformly modulated evolutionary random process. It can also be seen that the seismic-wave speed has a considerable influence on structural responses, which are caused by the pseudo-static displacement components.