Three-dimensional analysis of box girders considering nonlinear creep, shrinkage, and cracking effects

This paper presents a three-dimensional analytical framework for evaluating the structural behavior of box girder bridges, with particular emphasis on long-term effects such as creep, shrinkage, and shear lag–factors often neglected in traditional one-dimensional analyses. The proposed methodology integrates advanced material models and numerical strategies to simulate sustained loading and environmental influences, thereby improving the accuracy of stress and deformation predictions crucial for reliable bridge assessment. A rate-type creep formulation is developed based on the continuous retardation spectrum, removing the need to recompute Kelvin-chain stiffness parameters at each time step. Both EuroCode 2 and Model Code 2020 creep laws are incorporated, with approximate creep functions obtained through the PostWidder inversion technique. Cracking is represented using a continuous damage mechanics framework, enabling the gradual simulation of concrete degradation and crack evolution. The implementation is carried out in Abaqus/Standard through user subroutines and implicit time integration. The framework accurately models both reinforced and prestressed concrete structures, accounting for nonlinear creep, cyclic loading, shrinkage, cracking, and steel relaxation. A detailed case study of a three-span rigid-frame bridge further demonstrates the enhanced predictive performance of the model and confirms its consistency with experimental observations.