Crack width-based fragility curves for repairability of substandard beam-column joints

Post-earthquake observations have outlined the poor seismic performance of substandard reinforced concrete (RC) beam-column joints in existing buildings. They often exhibit significant cracking even under moderate intensity earthquakes, compromising the seismic performance of the entire building. This makes the quantification of their residual capacity and the definition of reliable repairability thresholds critical. Different approaches are available in the literature to establish the repairability of RC joints. However, a simple crack width-based criterion is required for practitioners during in-situ inspections. This study deals with the definition of crack width-based fragility curves relying on numerical analyses. Those are carried out by using the validated finite element (FE) models, being capable of reproducing the initiation and development of cracks in RC joints. To this end, the uncertainties in material properties, influencing the seismic performance of structural components, are accounted for different joints. In particular, experimentally validated FE models are evolved to stochastic level by generating random variables of material properties with the stratified sampling scheme. Fragility curves representing a certain level of probability of exceeding the defined crack width at the joint back, joint core, and beam-to-joint interface are developed. An application of the proposed methodology for in-situ inspections is also presented, and the results of in-situ measurements of residual crack width from real buildings damaged by recent earthquakes are used for the validation.