Seismic drift demand on multi-storey buildings in Sri Lanka due to long-distant earthquakes

Abstract

Intra-plate seismic activities in Northern Indian Ocean region below Sri Lanka, can be a possible threat of seismic hazard in terms of large magnitude long-distant earthquakes. Hypothesized seismic events with magnitudes 8, 7.5, 7 and 6, have been simulated based on this source by using the stochastic approach with estimated parameters for the Sri Lankan region. The crustal rock stratigraphy of the country consists mostly of crystalline rocks of Precambrian age, which governs the estimation of seismo-geological parameters were found to compare well with the well-known `hard rock’ conditions. Seismic response of structures from two major cities (Colombo and Hambantota) in the country was evaluated in terms of drift demands and base shears. The study includes both rock and soil sites. The soil amplification was carried out using the Extended Component Attenuation Model (ECAM) developed for typical intra-plate regions. Results show that, the base shear demands are far more significant than the drift demands for structures directly supported on rocks. Soft storey buildings directly founded on soil may experience higher drifts greater than allowable limits in some codes of practice. This suggests that important structures may need to be assessed using proper standards.