Large-scale simplified seismic risk mapping of residential buildings through rapid visual screening

Seismic risk assessment is of paramount importance to reduce fatalities and economic losses following major earthquakes. In seismic prone regions, with significant percentages of non-seismically designed buildings, large-scale rapid procedures to carry out such an assessment assume particular importance to identify the main building typologies at risk and to prioritise the allocation of resources. This paper presents the expedite seismic risk mapping of nearly 3'000 residential buildings in the province of Blida, in Northern Algeria, a region that has witnessed, in the recent past, major earthquakes causing significant human and economic losses. Based on the data collected during the field surveys, an index-based rapid visual screening (RVS) methodology available in the literature was adopted and adapted to the case-study RC building portfolio. The RVS methodology provides a seismic risk index based on the hazard level at the building's site, the structural vulnerability, and the exposure level. The hazard is defined by a proper intensity measure (peak ground acceleration or spectral acceleration) whereas the vulnerability is characterised as a function of a number of parameters related to the seismic response of RC buildings (e.g. lateral supporting system, in-plane and elevation irregularity, seismic code compliance). In turn, the exposure component of the index is related to the number of occupants and to the type of use of the buildings. The results of this study are useful for preliminary identification of buildings (or building classes) prone to higher risk and to assist decision-makers in the implementation of seismic risk reduction strategies.