Cracking behavior of partially prestressed concrete pier caps: Field evidence, nonlinear modeling, and implications for code-based crack control

Partially prestressed concrete (PPC) is widely used in bridge substructures because it combines the stiffness of prestressing with the ductility of reinforced concrete. However, current crack control provisions are largely derived from reinforced or fully prestressed concrete and have not been validated for PPC members under real service conditions. This study investigates the cracking behavior of 113 in-service PPC pier caps from the Ben Luc – Long Thanh Expressway in Vietnam through field measurements, nonlinear finite element analysis, and code-based evaluation. Field inspections revealed that cracking occurred in 87 pier caps, with maximum crack widths reaching 0.545 mm and crack depths exceeding the 50 mm concrete cover, indicating a potential durability concern despite full compliance with AASHTO LRFD and ACI 318 crack control requirements. A three-dimensional nonlinear finite element model incorporating concrete fracture mechanics and prestress–crack interaction predicted a maximum crack width of 0.448 mm and reproduced the observed crack localization at pier–cap junctions and bearing regions. Comparisons with ACI 224R and AASHTO LRFD formulations show that standard empirical models may underestimate crack widths, in some cases by more than 40%. This discrepancy is attributed to the distinctive cracking mechanism of PPC, in which prestressing tends to suppress distributed multiple cracking while promoting strain localization and wider individual cracks. The results suggest that current crack control provisions may be non-conservative for PPC pier caps and that nonlinear fracture-based analysis offers a more reliable basis for serviceability assessment.