Enhanced Catenary Action Prediction of RC Structures Through Improved Steel Bar Material Model

• Steel bar bilinear engineering stress-strain model undermines CTA numerical prediction. • Proposed EnSSC model employ two scalars to account for steel bar necking and fracture. • Predicted load-deflection responses using EnSSC model aligns closely with experiments. • EnSSC model greatly improves predictions of energy dissipation and ultimate capacity. • ENSSC achieves stage-by-stage agreement between numerical and experimental crack initiation, propagation, and patterns. Progressive collapse resistance of reinforced concrete (RC) structures subjected to column removal is governed by large-deformation mechanisms driven by the post-yield behavior of reinforcing steel. This paper evaluates how the choice of steel engineering stress-strain representation as opposed to true stress-strain with necking and fracture affects numerical behavior predictions and compares these predictions with published test data on RC beams, frames, and slab-beam subassemblies under a removed column scenario. A tri-linear constitutive material model for reinforcing steel bars was developed based on true stress-strain behavior enhancing the bi-linear model and creating an Enhanced Stress-Strain Curve (EnSSC). The proposed model is simple, relatively easy to establish and utilizes calibration coefficients to convert engineering stress-strain behavior parameters into true parameters. The paper findings show that engineering stress-strain models lacking necking and fracture consistently underpredicts ductility and peak capacity. Conversely, enhanced stress-strain models incorporating explicit necking and fracture provide substantially better agreement with experimental load-deflection curves. The improved fidelity is most pronounced in the catenary dominated phase where large steel tensile strains govern ultimate capacity. This study demonstrates that integrating the proposed enhanced steel stress-strain curve into the numerical model significantly improved the numerical prediction of catenary action, resulting in improved estimates of energy absorption and more accurate simulations of RC structure behaviors under progressive collapse scenarios. Therefore, the proposed enhanced steel model can lead to more robust and reliable numerical simulations.