30.6 Conclusions

Back

For short-span structures, the ground spatial effects are negligible, and the seismic analyses using RSM,

PEM, or THM (with a sufficient number of samples) are relatively close to one another provided that the

ground accelerations have been produced properly, and so are almost equivalent. Although they have

almost the same accuracy level, their efficiencies are quite different. Of the three methods, if the structural

models are rather complex (e.g., the FEM models have thousands or more DoF and need dozens or

hundreds of modes for mode superposition), then the PEM will have the highest computational

efficiency.

For long-span structures, the wave passage effect is an important factor for structural seismic

responses. The influence may produce more conservative, or more dangerous, designs, which is difficult

to predict by intuitive experience. Thus, computer-based analysis is a preferable choice. The PEM is

comparatively efficient and accurate, and is recommended. If the apparent seismic wave speed is not

available, then a few possible speeds can be taken for computation, with the most unfavorable results

being used in the practical design. The reasonable selection of an incoherence model for a special region

needs further study, but its influence seems to be much less than that caused by the wave passage effect.

Therefore, for less important long-span structures, the incoherence effect can be neglected. The influence

of nonstationarity is also significant for very flexible long-span structures, and should be taken into

account. The PEM, combined with the precise integration method, provides a powerful tool for such

nonstationary analysis.

Навигация