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Modeling Beam-Column Joints in Fragility Assessment of Gravity Load Designed Reinforced Concrete Frames

Çelik, Ozan Cem
Ellingwood, Bruce R.
Reinforced concrete (RC) frame structures customarily have been designed in regions of low-to-moderate seismicity with little or no consideration of their seismic resistance. The move toward performance-based seismic engineering requires accurate reliability-based structural analysis models of gravity load designed (GLD) RC frames for predicting their behavior under seismic effects and for developing seismic fragilities that can be used as a basis for risk-informed decision-making. This analytical approach requires particular attention to the modeling of beam-column joints, where GLD frames differ significantly from their counterparts in high-seismic areas. This article focuses on modeling shear and bond-slip behavior of beam-column joints for purposes of seismic fragility analysis of GLD RC frames. The joint panel constitutive parameters are defined to replicate the experimental joint shear stress-strain relationships, while the effect of bond-slip is taken into account through a reduced envelope for the joint shear stress-strain relationship. The joint model is validated using two full-scale experimental RC beam-column joint test series. A fragility assessment of an existing three-story GLD RC frame reveals the importance of modeling shear, anchorage, and bond-slip in joints of GLD frames accurately when performing seismic risk assessments of buildings.