埋込み剛基礎の動特性に基づく動的擬似3次元効果の考察 : 境界要素法による動的擬似3次元効果に関する研究(その2)

抄録

In this paper the effect of viscous dashpots introduced in two-dimensional representations on the response of structures due to seismic waves is examined by the boundary element method. To clarify the mechanism of approximate three-dimensional effect two embedded foundation system is analyzed. First the boundary element formulation of the soil-structure interaction problem for the case of rigid foundations embedded in an elastic soil is developed in conjunction with a substructure approach. It is worthy of note that an appropriate approach has to be taken for the approximate three-dimensional analysis to obtain foundation input motions and driving forces. Using the method two-dimensional and approximate three-dimensional analyses of rigid foundations embedded in a soil are made and results are compared with three-dimensional ones obtained by the boundary element method(Yoshida et al., 1986). Rigid foundations embedded in a finite soil layer underlain by a rigid rock are also analyzed to investigate the effect of soil layering. Results show that addig dashpots gives a good estimation of three-dimensional effect as long as a single foundation is embedded in a half space and that it gives excessive radiation damping for multiple foundation system and foundations embedded in a layered soil. In the latter part of this paper above mentioned approximate three-dimensional effect is investigated by considering a one-dimensional soil column supported by dashpots and also by analyzing the distribution of radiated energy. It is clarified from one-dimensional analysis that adding dashpots tends to increase real parts of impedance functions while imaginary parts remain almost unchanged. Comparing distribution patterns of radiated energy clearly shows that the radiated energy is too rapidly absorbed by additional dashpots and that the existence of an adjacent foundation or a soil layer may be underestimated.