Simulation and damage models for performance assessment of reinforced concrete beam-column joints

Performance based earthquake Engineering requires robust analytical tools for obtaining the structural response, damage assessment, as well as for performing reliability analysis. This research effort advances the numerical modeling of reinforced concrete structures by enabling simulation of inelastic beam-column joint behavior and reduced load carrying capacity of structural frames resulting from joint damage. The behavior of beam-column joints has been researched extensively over the past forty years through experimental studies on isolated joints in reinforced concrete subassemblies. This study focuses on the influence of joints on the overall frame behavior and the effect of modeling uncertainties on the response prediction. The analytical models proposed in this research are implemented in the OpenSees environment. Joint elements are formulated to simulate the nonlinear response of joints in two and three-dimensional models under cyclic loading. Proposed joint elements capture both geometric and material nonlinearities. A collection of nonlinear constitutive rules with cyclic deterioration are implemented to facilitate modeling the inelastic behavior associated with shear panel deformations and the slip of longitudinal reinforcement anchored in the joint. A generic damage model is proposed and implemented following the object-oriented architecture of OpenSees. The damage model incorporates existing damage formulations for representing deteriorating parameters in component force-deformation relationships and for component performance assessment. Calibrated modeling parameters are provided for seismically detailed code-conforming joints, and with minor calibration the same methods are used for modeling older (non-conforming) designs. The generic damage model allows one to present the damage indices as the engineering demand parameters and define limit-state boundaries for reliability analysis based on component damage. The sensitivity of the joint response and the nonlinear materials to modeling parameters are formulated for application through the reliability analysis toolbox of OpenSees. Applications of the proposed performance modeling tools are demonstrated through reliability simulations to compute the probabilistic distribution of damage in the joints, considering variability in both modeling and material parameters.