Numerical modeling of reinforced concrete columns strengthened by external steel collars and steel bars

This study investigated numerical modeling for reinforced concrete columns strengthened by external hollow structural section (HSS) steel collars and external steel bars. The main objective of this study is to numerically assess the seismic performance of columns strengthened by external steel collars and external steel bars. The experimental test data of two control columns, four steel-collar-strengthened RC columns with external steel bars, performed by Panyakapo et.al. (2024), were taken as benchmarks for the validation of numerical analysis. The implementation of finite element models for RC columns was performed in the OpenSees program. The fiber-based displacement nonlinear beam-column element was used to model the behavior of RC columns. The reinforced concrete material properties, which were subdivided into fiber sections, were defined based on the material constitutive laws of confined and unconfined concrete as well as steel materials for both internal and external longitudinal steel bars. The calculation of passive confinement properties of HSS collars was based on the lateral confinement calculation. The accuracy of the numerical prediction was validated by comparing hysteretic curves of load and deformation responses. The results showed that the predicted numerical responses closely captured the test results in terms of peak load and ductility with below 10 % difference in control columns and 5 % difference in strengthened columns.