The paper addresses the influence of soft local site on the propagation of incident waves and the effect of non-uniform ground motions on the building response. A previously developed coupled BEM-FEM algorithm is employed for the analysis directly in time domain. The inertial and kinematic interaction between the soil and building is therefore automatically included. In order to limit the influence factor and for a clearer evaluation of the results the Ricker wavelet incidence is considered, since it has a well defined bounded range of dominant frequencies. It is assumed that the local site has a valley shape bounded by a half space of hard soil. The site has a uniform soft soil, medium soil or a soft layer over medium subsoil. The building is a ten-storey frame structure. For a comparison with common design calculations the effect of frequently used El-Centro ground motions is considered as well.
The investigation shows that the local site can significantly affect the propagating waves in the site area. The alteration of the characteristic of the incident waves determines the ground excitation of the building foundation. Consequently, the response of the building is strongly affected. Besides the characteristic alteration the shape of the local site has strong influence on the spatial variation of the ground motions that excite the building non-uniformly. In the common design procedure or even in most of the research works -for simplicity- uniform ground excitations are often assumed. The study reveals that an assumption of uniform ground excitation is not able to reflect the nature of the non-uniform ground motions. In order to obtain more reliable response of the building the influence of local site properties is significant. Otherwise, the activated forces in the building, and consequently the damage potential of the ground motions can be underestimated.