Large bridge structures that are subject to Alkali Silica Reaction (ASR) and Delayed Ettringite Formation (DEF) are a major cause of concern; there is a need for understanding the internal deterioration mechanism and their prognosis. The Compatibility Strut-and-Tie Method (C-STM) is used to model the behaviour of experimentally tested C-beam specimens subject to varying degrees of ASR/DEF deterioration as well as varying degrees of associated corrosion of the rebars. The simulation accounts for age-modified cover and core concrete material properties, and the resulting passive prestress effects on the longitudinal and transverse reinforcement. An increase in strength and stiffness of the specimens with an increase in the passive prestress effect is observed. However, the energy absorption capacity of the heavily deteriorated specimen saw a 59% reduction. Post-peak stress softening of the diagonal arch-strut successfully simulates the embrittlement and decrease in deformation capacity of the most heavily deteriorated condition. Corrosion of the longitudinal and transverse reinforcement in the beam-column joint is found to decrease the load and deformation capacity by some 35%, and the energy absorption by 86% after 60 years of rebar corrosion. The mode of failure for all the specimens is the crushing of the diagonal concrete arch-strut in the beam-column joint. The progression of nonlinear events that lead to failure of large beam-column joints that are affected by varying levels of ASR/DEF deterioration are successfully tracked by the C-STM. © 2020 Elsevier Ltd