International Concrete Abstracts Portal

In the seismic design of reinforced concrete (RC) bridge structures, torsion frequently occurs in piers and may degrade their effective stiffness. However, this effect is not explicitly considered in contemporary seismic design codes and the existing literature. To address this gap, this study utilizes a calibrated finite-element model to conduct a comprehensive parametric analysis, quantifying the impact of torsion on the effective stiffness of square RC piers under combined loading. The findings reveal a non-linear response: while effective stiffness remains stable or marginally increases at low torsion levels, it degrades significantly once the torsion ratio (T/Tu) exceeds 0.4–0.5. The rate of this degradation is primarily governed by the axial load ratio and the longitudinal reinforcement ratio. Furthermore, the sensitivity of effective stiffness to these design parameters, along with longitudinal reinforcement spacing, is highly dependent on the applied torsion level. Drawing on these results, this study proposes an empirical equation to predict a torsion-influence coefficient. This formulation facilitates the accurate estimation of effective stiffness for RC piers subjected to coupled bending and torsion, thereby enhancing the reliability of performance-based seismic design.

This paper presents post-fatigue residual punching shear strength experiments of two identical sections reinforced by glass fiber-reinforced polymer (GFRP) rebar in a large bridge deck (15.24 m x 3.89 m x 0.21 m) supported by steel girders spaced at 3.05 m. The experiment was designed to isolate the influence of fatigue loading type on residual punching shear strength. The sections have experienced 3 million cycles of service loads, one using pulsating loads (PL) and the other using rolling loads (RL). Although the RL section suffered more stiffness degradation (71%) than the PL section (54%), both had comparable punching shear strengths (Vu), within 4%. Available equations, including ACI and CSA code regulations, underestimated Vu by 24-54% because they do not account for end restraints, which generate compressive membrane effects that significantly increase the punching shear capacity of concrete slabs. Nonlinear finite element analysis was conducted and used to examine interactions between multiple loading axles as well as offset of the loads from the center. Vu under 2 half axles spaced at 1.2 m (i.e., the 2 axles likely to interact in design truck CL-625 of the Canadian Highway Bridge Design Code) increases by only 34% compared to a single load.

For the assessment of existing reinforced concrete slab bridges, the shear capacity under concentrated loads and transition to flexural failure are under discussion. Previous research showed an increased shear capacity for slabs under concentrated loads close to the support, so that for assessment, positions farther from the support became governing. This experimental research studies the flexural and shear capacity of reinforced concrete slabs under concentrated loads. For this purpose, six slabs representing 1:2-scale continuous slab bridges were tested at various positions from the support and along the width. The results show two main failure modes: flexural failure (onset of yielding of the reinforcement), and shear failure. Secondary punching was observed as well. The comparison between the test results and calculation methods shows that all considered methods perform reasonably well when both shear and flexure are considered, and the effective width in shear is included, with average tested-to-predicted capacities between 0.92 (Regan’s method) and 1.39 (Extended Strip Model [ESM]) and coefficients of variation between 15% (Regan’s method) and 25% (ACI 318-19 and Eurocode 2). These insights can be used for the assessment of existing reinforced concrete slab bridges.

In the Netherlands, existing reinforced concrete solid slab bridges require assessment for shear. Skewed slab bridges form a subset of this category. Previous experiments showed that stresses concentrate in the obtuse corner, which becomes governing for shear, and that the shear capacity in skewed members is reduced. The presented series of experiments studies the shear capacity of reinforced concrete slabs under concentrated loads. In total, five skewed slabs are tested, resulting in 15 shear experiments. The parameters that are studied are the skew angle, the reinforcement layout, the distance between the load and the support, and loading near the obtuse or acute corner. The results are compared to existing calculation methods and recommendations for determining the acting shear stress and shear capacity, which lead to reasonable results. Ultimately, the insights from these experiments can be used for the assessment of existing skewed slab bridges.

The aging reserve of bridges in the United States needs load-rating assessments to ensure sufficient load-carrying capacity and safety. Bridges without sufficient capacity to carry the legal loads are load-posted. These load limits reroute traffic, which may result in traffic congestion and longer routes, and, thus impose inconvenience on travelers and significant costs to society. This paper investigates the potential for improvement in the load-rating process for simple-span concrete slab bridges. Such bridges are load-rated by the Texas Department of Transportation using simplified load-rating procedures, which are intended to be conservative and can have varying degrees of accuracy compared to the actual behavior of bridges. Finite element modeling was conducted to simulate the expected behavior of a representative concrete slab bridge, and the model was calibrated using experimental test data. The equivalent width results were compared with estimates from established design specifications and empirical guidelines. The methods developed for concrete slab bridges with integral curbs provided accurate estimates of moment demand for curb sections. In addition, an established analytical approach in the literature accurately predicted the moment demand for interior slab sections under one-lane loading, while the equations in current design specifications performed well for two-lane loading cases.