Site Effects Assessment and Soil-Structure Resonance in The Old Center of Algiers

Abstract

During earthquakes affecting urban areas, we often deplore damages to buildings. The pattern of these damages depends on the characteristics of the event, the site response, and the vulnerability of exposed structures. The old urban center of Algiers is a densely populated district. Preserving human lives is therefore of primary importance. Soil-structure interaction is an important factor in site-wide risk assessment. When the ground and supported buildings have similar frequencies, this interaction induces a phenomenon called resonance. In this study, the Standard Penetration Test (SPT) and the Horizontal-to-Vertical Spectral Ratio (HVSR) of microtremors techniques were applied in order to evaluate the fundamental frequencies of the ground; as well as the fundamental, longitudinal, and transverse frequencies of each selected building. This investigation aimed to detect the existence of the resonance phenomenon. If we assume that the sample of buildings tested is representative of the urban district of the area studied, we can conclude that buildings in the old center of Algiers, are not exposed to a resonance phenomenon. The same conclusion was observed from the analysis of the results of the post-seismic investigations obtained from two major past earthquakes, El Asnam on 10/10/1980 and Boumerdes on 21/05/2003. The first one is considered as a distant event from Algiers, while the second one is at a nearby location.