| Abstract: | In Eastern Canada, most of moment resisting reinforced concrete frames with unreinforced masonry infill (MI-MRF) buildings were constructed between 1915 and 1960. These pre-code structures, in terms of seismic requirements, are considered vulnerable to earthquake due to insufficient ductility and resistance. The goal of this study is to provide a quantitative assessment of their seismic performance using fragility functions. Fragility functions represent the probability of damage that corresponds to a specific seismic intensity measure (e.g. peak ground acceleration at the site). Based on a structural characterisation study on existing buildings in Québec region, a case study three storey–three bay MI-MRF was selected as representative for mid-rise buildings. Pushover analyses were conducted on a nonlinear model of the infill frame to obtain the corresponding lateral load-deformation capacity curve. The nonlinear behaviour of the reinforced concrete beams and columns was modelled with concentrated plastic hinges at members’ ends and a modified strut-and-tie model was used for the infill to account for multiple failure modes. A simplified probabilistic nonlinear static procedure was applied to obtain the seismic demand model at increasing levels of seismic intensity. Fragility functions were then developed using an experiment-based damage model that correlate the extent of damage to the displacement demand. Damage assessment using the developed functions was conducted for an earthquake scenario compatible with the design-level seismic hazard in Quebec City with a 2% and 10% probability of exceedance in 50 years. The developed functions and methodology are particularly useful in probability-based seismic loss assessment and in planning mitigation solutions. |
