Evaluation of Shear Capacity Degradation in Normal Concrete Bridge Decks under Coupled Effects of Fatigue and Wet Environment

Reinforced concrete (RC) bridge decks in tropical monsoon regions (e.g., Mekong Delta River, Vietnam) are frequently subjected to the coupled effects of increasing heavy-vehicle traffic and prolonged wet conditions during rainy seasons. This paper investigates the degradation mechanism of punching shear capacity in existing RC decks using the Critical Shear Crack Theory (CSCT) combined with a surface degradation model calibrated from push-off tests. The study synthesizes and contrasts experimental observations on Normal Weight Concrete (NWC) interfaces subjected to pure shear under cyclic loading, in both dry and submerged environments. The results suggest that current design codes (TCVN 11823, AASHTO LRFD, JTG 3362, and JSCE) may overestimate the shear capacity of cracked members by neglecting aggregate attrition, water lubrication, and wash-out of crushed particles within cracks. Notably, reversed cyclic loading-representative of wheel actions across existing cracks-induces much more severe damage than pulsating loading. The paper provides practical warnings for assessment and strengthening design of deteriorated bridge decks in wet environments.