Drift-Based Component Fragility Functions and Nonlinear Backbones for Existing Non-Ductile Exterior Beam-Column Joints With Different Detailing

Abstract

The damage after an earthquake in Reinforced Concrete (RC) moment-resisting frames is often observed at the beam-column joints due to their vulnerability associated, among others, with poor structural details. An important issue is to estimate the rotational capacity of typical existing exterior joints and to evaluate their fragility functions at different damage states as a tool for loss assessment of RC buildings. With this aim, a macro-model of the connection subset was developed and calibrated on eleven experimental data available in literature or yet unpublished, characterized by the absence of shear reinforcement within the joint panel zone and by two typical longitudinal beam bar anchorage layouts, namely hooked and bent-in. For both the structural details, three ranges for the joint panel rotations were proposed corresponding to three distinct damage conditions defined as a function of the rotation capacity, as low, medium, and severe damage, corresponding respectively to the first cracking, extensive damage/peak capacity in the joint, and incipient collapse. Furthermore, bi-linear and tri-linear backbones for the non-linear moment-rotation spring of the RC joint were suggested, both for practitioner use and for the research field, depending on the required level of accuracy. Through an extended parametric analysis, 20,952 exterior joints were numerically simulated. The analyzed joints were defined by selecting plausible combinations between geometrical, mechanical, and structural input parameters. The numerical results were used to build the fragility functions for three damage states.