Seismic Soil-Structure Interaction as a Potential Tool for Economical Seismic Design of Building Structures

Abstract

Noting that contemporary seismic design codes have become more and more demanding in terms of requirements related to design forces and deformations for buildings, this paper attempts to demonstrate that it could be prudent to consider the introduction of soil-structure interaction (SSI) provisions into local codes in order to potentially offset the costs incurred by the high demand for base shear attributed to site amplifications by soft soil sites as per current code requirements. This mostly beneficial effect of site soils is as a result of lengthening of the fundamental period and of the mostly increased effective damping of the overall system due to SSI. After introducing the basic concepts of dynamic SSI, the paper demonstrates that if SSI provisions in some international codes are properly adapted, a substantial reduction in the base shear force could potentially be achieved so that the sizes of structural elements would also be proportionally less. With this, the paper attempts to address the legitimate concerns of many design engineers regarding the likely escalation of construction costs associated with the stringent requirements of contemporary seismic design spectra for soil sites that are expected to be introduced in the Ethiopian seismic code currently under revision.

Keywords: soil-structure interaction, fixed-base structure, flexible-base structure, period lengthening, effective damping, base shear, site amplification