Seismic evaluation of the southbound Stellenberg Interchange Bridge, <scp>B5593</scp> , in South Africa

Abstract This study presents a nonlinear finite element assessment of the seismic vulnerability of Bridge B5593, located in the south‐western region of South Africa. Previous evaluations identified a high likelihood of column failure; however, these were based on linear material models incapable of capturing damage evolution. In this investigation, a high‐fidelity three‐dimensional solid‐element modeling framework is developed using the concrete damage plasticity (CDP) constitutive model to explicitly simulate tensile cracking, compressive crushing, stiffness degradation, and progressive failure in reinforced concrete columns. The model is verified against global structural properties and subjected to nonlinear time history analyses for peak ground accelerations ranging from 0.05 to 0.20 g. Results indicate that, while all columns possess sufficient shear capacity, flexural demand governs the response, with several columns exceeding their bending moment capacities by up to 82%. Importantly, tensile damage initiates at low seismic intensities (0.05 g) and propagates rapidly with increasing excitation, leading to significant stiffness degradation and localized failure, particularly in shorter columns. These findings highlight that material‐level damage progression provides critical insight beyond conventional force‐based assessments. The adopted modeling approach is intended as a local damage‐focused complement to conventional beam‐based global analyses, enabling detailed evaluation of failure mechanisms not captured by standard methods. Although simplifications such as fixed‐base conditions, idealized bearing behavior, and uniform ground motion were adopted, these do not affect the identification of critical vulnerabilities. The results demonstrate that Bridge B5593 is susceptible to moderate to severe damage at design‐level seismic events, with a significant risk of partial or global collapse at higher intensities. The study underscores the need for refined assessment approaches and potential retrofit strategies for existing bridges in regions of emerging seismic risk.