Development of predictive expressions for drift-based damage states for precast columns in socket foundations

Abstract

Precast concrete structures are composed of columns that exhibit significant flexural behavior, high aspect ratios, and substantial deformation and drift capacities. The existing experimental and analytical expressions found in the literature regarding the deformation and displacement capacities of columns are generally inadequate and not directly applicable to precast columns. Therefore, a comprehensive investigation into the damage capacities of precast columns is necessary. In this study, simplified expressions were developed to estimate drift ratios corresponding to various damage states of square precast columns. The effects of several design parameters, including square section depth, aspect ratio, axial load ratio, reinforcement ratios, material strengths, and embedment depth, on the damage behavior of socket columns were evaluated. Initially, based on existing experimental studies on socket foundations, a simplified equation was proposed to estimate the rotational stiffness of the socket column-foundation connection. Then, a parametric study was conducted, and to generate sufficient data, different column models were created using information obtained from previous studies on precast structures, and pushover analyses were performed. The primary damage states considered in these analyses included reinforcement yielding, concrete cover spalling, longitudinal bar buckling, and concrete crushing. Based on the analysis results, polynomial regression analyses were used to develop simplified expressions to estimate drift ratios. These expressions were found to predict experimentally measured drift values with satisfactory accuracy. Among the evaluated design parameters, the aspect ratio was found to significantly affect drift demands. Additionally, fragility analyses indicated that as the aspect ratio increases, socket columns require larger embedment depths to mitigate damage states related to longitudinal reinforcement yielding and cover concrete spalling.