Quantifying the effect of retrofitting on the seismic collapse performance of a representative mid-rise reinforced concrete building in Beirut

Abstract

Lebanon is situated in a region of significant seismic hazard. Seismic design codes, however, were not strictly enforced until 2012 with the publication of the second edition of the Lebanese earthquake standards. This, combined with a lack of construction regulation and oversight caused by the onset of the Lebanese civil war in 1975, has led to a structurally deficient building stock in need of rehabilitation. Limited studies that investigate methods of improving the seismic performance of buildings constructed prior to the 1990s are available. This project aims to assess the effect of several retrofitting schemes on the seismic collapse performance of an 8-story non-ductile reinforced concrete frame building in Beirut. This typical structure is characterized by wide-shallow beams, high aspect ratio columns, insufficient transverse reinforcement, unreinforced wide beam-narrow column joints, and lap splices located in potential plastic hinge regions. Three retrofitted versions of the building are designed and considered in this study. In the first version, the columns are concrete jacketed using the minimum jacket thickness and reinforcement. In the second version, the concrete column jackets are designed to sustain the column seismic demands obtained using the equivalent lateral force method. The third version is identical to the second but longitudinal carbon-fiber reinforced polymer (CFRP) strips are added to the beam elements. The seismic assessment is accomplished using the Federal Emergency Management Agency (FEMA) P-695 methodology. Analytical models of the buildings are developed in the Open System for Earthquake Engineering Simulation (OpenSees) framework using the lumped plasticity approach, non-linear pushover and incremental dynamic analyses are performed, and collapse fragility functions calculated. Results show that all the retrofitting procedures investigated in this study are effective. The probability of collapse at the maximum considered earthquake intensity is reduced from 87percent for the unretrofi