Numerical Investigations of Precise Detailing for Rectangular-to-Circular Irregular Column Joints in a RC Structure

Architectural and aesthetic demands may require complex detailing of structural components that are not covered in design provisions and guidelines. Large-scale specimen testing is not always feasible due to the time requirement, cost, and complexity of test setup. Therefore, accurate finite element analysis can be a viable alternative for complex joint detailing. In this study, one such reinforced concrete detailing issue was investigated explicitly, where a longer (double height) circular column was connected to a shorter but wider rectangular column at the floor level of a high-rise residential building in Dhaka. Primarily, a 3D finite element (FE) integrated model of the entire building was developed by a commercial package, ETABS v 20. In this process, actual building geometry, material properties, and loading (including wind and earthquake) are strictly emulated following relevant codes and standards to determine the envelope of forces at the joint. Then, after substantial trial and error, three joint details were selected for evaluation in the general-purpose finite element program, ABAQUS. The concrete damage plasticity model was used to model the concrete, whereas the bilinear elastic-plastic model was chosen for modeling the steel reinforcements. The static pushover analysis was conducted to determine the von Mises stress distribution, moment-deformation capacity, ductility, and damage states of the joints. It was observed that joint detail-3, where additional rebars (of the same diameter as the column reinforcement) were provided up to the development length, outperformed the other joints in terms of moment capacity and ductility. In this detail, the concrete failed before the rebars, and the rebars reached their yield stress near the plastic hinge rotation. The recommended joint also showed a local stress concentration distributed over a larger area, which indicates greater utilization of rebar strength. This study may help researchers and practicing engineers to understand how the FE technique grips complex joint detailing and yield solutions for field problems that are not generally available in textbooks or code provisions.