Engineering estimation of topographic effects in site response analysis


Despite the irrefutable amount of theoretical and field evidence of the impact of topographic effects on the local response at a site the engineering community still lacks practical methods for its consideration in a standard routinely basis. The incorporation of topographic effects into site response analysis has been a major challenge to engineers as it involves coupling between mechanical and geometric modifications to the incident seismic waves, which at the same time demands for field data that is rarely available to the practicing engineer. On the other hand, it has been observed that the main signature of topographic effects, besides the expected change in frequency con tent, is its spatial variation. These complexities combined to the field data required to build fully coupled mechanical-geometrical models have resulted in complete under consideration of these effects. In this work we follow a rational approach to study the effect of surface topography on the response at local sites after formulating the problem following a diffraction perspective. Since this work is framed in an engineering context our main result is a method to incorporate the effect of surface topography in ground response analysis. Although the method requires numerical simulations we show that if the analyst brings into the problem the dynamic properties of the structure for which the analysis is conducted in the first place very moderate models may be required. These idea leads to the concept of size conditioned response spectra which uses a target structural response spectra to fix the size of the computational model. The resulting numerical domain turns out to be of manageable size thus it can be handled with standard computing resources. Although our proposed approach is limited to surface topography the combination of the theory of diffracted waves and the consideration of the structural response creates new venues to advance in understanding the problem of topographic effects.


Palabras clave

Efectos topográficos, Espectro condicionado por tamaño, Difracción