An Analytical Model to Evaluate Short- and Long-Term Performances of Post-Tensioned Concrete Box-Girder Bridges Rehabilitated by an Ultrahigh-Performance Concrete Overlay

Potentially unfavorable stress redistributions could occur in post-tensioned concrete box-girder bridges upon deck rehabilitation by an ultrahigh-performance concrete (UHPC) overlay. The reason for such redistributions is that the deck forms an integral part of the load-resisting mechanism so that deck rehabilitation, namely, the process of removing the deteriorated deck and casting a fresh UHPC overlay, may cause large stress redistributions in the box girder. In addition, the significantly different shrinkage behavior between the freshly cast UHPC deck overlay and the old existing concrete deck below would result in restrained stress in the UHPC–old concrete interface. Therefore, how to evaluate the stress redistributions and the potentially unfavorable stresses in the box girder resulting from construction operations and the incompatible shrinkage is a crucial issue. Here, we propose an analytical model to assess the short- and long-term performances of the concrete box girder during and after deck rehabilitation. The analytical model was verified by using finite-element models incorporating the staged construction simulation and time-dependent behavior of materials. The model can be easily established and calculated with a great amount of time-saving compared with finite-element modeling, and it applies to different types of post-tensioned concrete box-girder bridges. The analytical model involves the balancing-load concept and the age-adjusted effective modulus method (AEMM). The balancing-load concept in the short-term analysis is to account for the prestressing force, and the AEMM in the time-dependent analysis is an effective tool to determine how stresses and strains vary with time due to the creep and shrinkage of a UHPC deck overlay. A parametric study was then conducted based on the analytical model, which involved the thickness of the deck layer to be rehabilitated and the addition of steel reinforcement in the new UHPC deck overlay. Analysis results indicated that pronounced tensile stresses developed in the UHPC deck overlay, which resulted from the restraint of the free shrinkage of the UHPC overlay by the subjacent concrete deck. An increase in the thickness of the newly cast UHPC deck overlay resulted in a decrease of the tensile stress in the UHPC deck overlay, and a rehabilitation thickness of 3.8–5.1 cm (1.5–2.0 in.) was deemed appropriate for the selected bridge according to the analysis.

Post-tensioned concrete box-girder bridges are one of the most common bridges worldwide. The concrete bridge deck, the surface of a bridge that carries the roadway, is most prone to damage in a bridge due to years of exposure to unfavorable environmental conditions and direct impact loadings from vehicles. The deck rehabilitation for deteriorated post-tensioned concrete box-girder bridges has become an urgent maintenance issue. However, potentially unfavorable mechanical behavior could occur in the bridge during a series of deck rehabilitation operations, that is, the process of deck removal and construction of a new deck. A careful evaluation of the bridge’s mechanical behavior during the entire deck rehabilitation construction process is essential to ensure a safe and feasible deck rehabilitation strategy. Here, we propose an analytical model to evaluate the bridge behavior during and after the deck rehabilitation, which offers an effective and time-saving tool for bridge engineers and researchers to rapidly assess the short- and long-term responses of post-tensioned concrete box-girder bridges. In addition, how rehabilitation thickness affects the bridge behavior during the construction was studied based on the analytical model, and then the appropriate rehabilitation thickness of the deck was recommended according to the analysis.