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稳随机地震响应问题,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.%Prestley's mathematical modelof non-uniformly modulated evolutionary random process takes intoaccount the non-stationary characteristics not only of the excitationintensity, but also of the excitation frequency components. Therefore,it has been considered as physically rather reasonable insimulating general earthquake excitations for a long time. Unfortunately, as this modelis expressed in terms of Riemann-Stieltjes integration, the relevantcomputation is very difficult. So far, this model is still considered asunacceptable by practicing engineers even for single excitationproblems. In order to simplify the computation, usually thenon-stationary characteristics of the excitation frequency components isignored, 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 modulateddifferential evolutionary random seismic excitations are analyzed bymeans of the PEM (pseudo excitation method), an accurate and efficientway. By using this method, the wave passage effect is strictly dealtwith, and the cross-correlation terms both between all participant modesand between ground excitations are accurately involved. This method isconvenient because the non-stationary random excitations are transformedinto deterministic excitations, and so ordinary step-by-step integrationmethods such as Newmark or Wilson- schemes can be directly used.In this paper, the precise integration method is used, and sothe computation efficiency has been further remarkably raised.rn A numerical example about an earth-stone dam built in China is given.Its finite element model has about 3 000 degrees of freedom and morethan 100 ground joints. The results show that it is significant forstructural components, which are sensitive to higher frequencies, toregard the excitations as non-uniformly modulated evolutionary randomprocess. It can also be seen that the seismic-wave speed has aconsiderable influence on structural responses, which are caused by thepseudo-static displacement components.
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