Seismic vulnerability and fragility of steel buildings

Abstract

The main goal of this article is to evaluate the structural behavior of steel buildings. The seismic performance ofa specific steel building located in the campus of the National University of Colombia in Manizales is assessed.The seismic demand is characterized by a peak effective acceleration of 0.25 g. Pushover analysis applied to alow-rise steel moment-resitant frame building and a low-rise steel braced frame building has shown theinadequate seismic behaviour of moment-resistant frame buildings, althoug the increase of the stiffness ofbraced frame buildings may induce seismic damage to non-structural elements sensitive to spectral acceleration.We have obtained fragility curves and damage probability matrices for the seismic demand anticipated by the Colombian seismic code for Manizales. We obtain specific relationships between yielding and ultimate capacityspectral displacements and damage states’ thresholds. These relationships can be applied to low-rise momentresistant frame and low-rise braced frame buildings. The comparison of the obtained expected mean damagestates and the vulnerability classes provided by the EMS-98 macro-seismic scale leads us classifying low-risesteel braced frame buildings and low-rise steel moment resistant frame buildings respectively into thevulnerability classes C and D-E. We clearly show that, stiffening buildings withconcentric braces leads to moreearthquake-resistant structures, and therefore with a significantly lower seismic vulnerability.