This paper explores the effect of bonding size on the shear performance of ultra-high-performance concrete (UHPC) and normal concrete (NC). The study includes two sets of direct shear tests on a total of 16 Z-shaped UHPC-NC bonded specimens. The first set consists of eight direct shear tests on the chiseled UHPC-NC interface with an average roughness of 4 mm (referred to as series C), from the authors’ previous study. The second set involves eight direct shear tests on the chiseled UHPC-NC interface with additional short shear steel rebars (referred to as series CS) that possess identical roughness to the first set of tests. The study discusses the failure modes, shear stress–slip behavior, and strain histories of the UHPC-NC interfaces with varying bonding sizes and shear mechanisms. A finite element model incorporating the cohesive zone model for the UHPC-NC interface was developed to gain insights into the shear bond evolutions. Our experimental results show that the two sets of direct shear specimens exhibit similar size effects in the shear stiffness, bonding strength, and interfacial slippage of the UHPC-NC interface. The use of shear steel rebars mitigated the impact of interfacial size on the bond shear behavior, thereby enhancing shear stiffness and reducing susceptibility to brittle damage. Numerical simulations indicate that the shear stress inhomogeneity coefficients for the CS specimens with bonding heights of 100 mm, 200 mm, 330 mm, and 440 mm were 1.2%, 1.8%, 11.9%, and 17.4%, respectively. The findings of this study provide valuable insights for optimizing UHPC applications in the repair and strengthening of concrete structures.

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.

This paper studies the feasibility of replacing damaged deck of posttensioned concrete box-girder bridges without the use of falsework to support the superstructure span. Parameters of the study included straight, curved, and skewed bridges, and simple versus multispan bridges. Deck replacement in posttensioned box-girder bridges requires special attention because the deck forms an integral part of the load-resisting mechanism and large precompression has been locked in by the posttensioning in the superstructure. The potential unfavorable stress reversals or redistribution during deck replacement should be carefully considered. In this study, practical options for lane closure and traffic rerouting were incorporated into the replacement strategies, and these options included temporal longitudinal and transverse replacements. Additionally, time-dependent properties for concrete and steel representatives of current construction practice were included in the finite-element model. Results indicated that full-depth deck replacement may be difficult and undesirable because the current AASHTO stress limits were violated in all four of the posttensioned box-girder bridges selected for the study. Additionally, the increase in permanent deflections through deck replacement was relatively large for these selected bridges, which is likely to result in degraded ride quality, safety, and poor drainage condition for the bridge. As a general trend, critical stresses at the top of the web and downward deflection of the girders were found to accumulate as the deteriorated deck was removed and a new deck cast.

Long-term exposure to a harsh environment leads to irreversible degradation of mechanical properties of fiber-reinforced polymer (FRP) profiles. Understanding the aging effects on pultruded FRP composites due to long-term exposure is essential. The moisture diffusion process plays a significant role in understanding material degradation of E-glass/polyester-reinforced polymer composite laminates exposed to hygrothermal environments. In this paper, the moisture diffusion process in pultruded (GFRP) composite bridge members is numerically simulated using the finite-element method. The moisture diffusion parameters were calibrated by gravimetric tests of pultruded composite thin plates. Gravimetric tests of three different rectangular specimens were conducted to investigate three-dimensional moisture diffusion at different temperatures and environments. The calibrated mass diffusion parameters were validated by comparing the average time-dependent moisture concentration obtained from non-Fick finite-element (FE) simulation with experimental results.