Reliability Assessment of Rehabilitated Buildings of Moderate Height

Abstract

Buildings that were designed according to earlier codes tend to have limited lateral load-carrying capacity when compared to buildings built in accordance with current seismic codes. This deficiency caused severe damage to existing buildings when subjected to earthquake loading. Over the past three decades, building codes have been updated with more stringent seismic demand requirements. The objective of the current study is to evaluate the seismic behaviour of an existing nine-storey office building, designed according to the ACI-318-63 code. Pushover static analysis, as well as seismic analysis of the building behaviour were conducted. Uncertainties in both the demand (load) on the structural system as well as capacity (resistance) were taken into account. An ensemble of synthetically-generated ground motion time history records was used to simulate earthquakes on both soft soil and rock sites using both stationary and non-stationary approaches. Randomness in structural capacity was modelled by selecting appropriate probability distributions for variations in both element dimensions and material strength. Aging of concrete was also taken into account. The Monte Carlo Simulation was used to incorporate various sources of uncertainty into the analysis. The performance of the existing building was evaluated. Different performance levels were defined for the structure in terms of the damage levels. The damage state of the building was quantified using the damage index proposed by Park et al. (1985) and modified by Kunnath et al. (1992). The results of the dynamic analysis were related to the damage index, story drift, roof drift and the static pushover analysis. The reliability approach was used to evaluate the effectiveness of different retrofitting schemes for the reinforced concrete columns of the existing building. The retrofitting schemes considered included increasing strength, ductility, stiffness and both strength and stiffness simultaneously.