Impact of Transient Thermal Gradients and Time-Dependent Effects on Prestressed Box-Girder Bridge Behaviour: A Coupled ANSYS-Based Investigation

Abstract

This study explores how real-world temperature variations and long-term material behaviour
influence the performance of a 45 m prestressed concrete (PSC) box-girder bridge using a
coupled ANSYS-based finite element approach. Instead of relying on simplified assumptions,
a transient thermal analysis was carried out to capture realistic temperature distributions,
revealing clear diurnal patterns with peak top-hot conditions around 13:00 h and bottom-hot
conditions around 04:30 h. The resulting temperature gradients were found to be strongly
nonlinear, with a sharp thermal drop across the top slab and a more gradual variation towards
the bottom slab. When these thermal effects were applied to the structural model, they
produced noticeable curvature and stress redistribution. Under top-hot conditions, the bridge
exhibited an upward camber, while bottom-hot conditions induced downward curvature. The
stress analysis showed that maximum tensile stresses developed at the soffit near midspan,
whereas the top slab remained predominantly in compression. Time-dependent analysis
further revealed a progressive reduction in prestressing force, driven by creep, shrinkage, and
relaxation, leading to a measurable shift in the neutral axis and expansion of tensile zones
over time. In the long term, deflection increased significantly, with creep identified as the
dominant contributor, while repeated thermal cycles further amplified deformation. The
combined analysis demonstrated that thermal and time-dependent effects interact in a
nonlinear and path-dependent manner, sometimes amplifying and sometimes counteracting
each other. Overall, the results clearly indicate that soffit tensile stress at midspan governs
serviceability, highlighting the limitations of conventional code-based assumptions and the
need for integrated analysis approaches for modern PSC box-girder bridges.