Seismic collapse assessment of mid-rise reinforced concrete buildings in Beirut

Abstract

Lebanon lies in an area that has been struck by several strong earthquakes and is thus classified as a region of moderate seismicity. Such large magnitude earthquakes, although rare, could result in considerable human and financial losses. Seismic regulations started being enforced in 2005, but prior to that most buildings were designed to resist gravity loads only, with little or no resistance to laterals loads. In addition, most of the construction sector suffered from poor design provisions and material quality during the Lebanese civil war (1975 – 1990). Therefore, it is important to assess the seismic performance of the buildings in Beirut and Lebanon. The objective of this study is to quantify the probability of collapse of some representative mid-rise reinforced concrete buildings if strong shaking occurs. This is achieved by compiling information necessary to develop detailed designs of such gravity load designed buildings. Mathematical structural models are developed using Open System for Earthquake Engineering Simulation (OpenSees) and a new joint model is calibrated to fit the joint types under study. Then, the structures are subjected to a set of systematically scaled ground motions from the FEMA P695 Far Field set. After using the analysis results to fit fragility curves for each building, the probability of collapse under the maximum considered earthquake is determined. The results of this study indicate that the building stock in Beirut has a high probability of collapse, greatly exceeding the limits set by FEMA P695. The results also indicate that joints, mainly exterior and corner ones, sustain significant damage and eventually lead to collapse. In addition, recommended locations of retrofits are proposed for each building. The results indicate the importance of spreading public awareness about the seismic vulnerability of the buildings stock in Beirut. It also constitutes an important step towards performing damage and loss analysis, enabling stakeholders and owners to choose between