International Concrete Abstracts Portal

Repeated vehicle loading causes a decrease in transverse joint stiffness in concrete pavements due to damage accumulation around dowel bars. The relationship between key design parameters and damage accumulation is not well established due to limited faulting performance data and a lack of experimental data from expensive full-slab testing. A novel laboratory test setup was developed to characterize damage development caused by repeated vehicle loads. This setup was used to characterize damage for a range of key parameters at a lower cost and level of effort compared to full-scale slab testing. The concept of beam deflection energy, DE_Beam, is also introduced. Experimental results were used to develop a DE_Beam prediction model. The novel test setup developed in this study enables the rapid evaluation of a variety of dowel materials and geometries, and experimental results can be used to improve current faulting prediction performance.

The aging reserve of bridges in the United States needs load rating assessment 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 that may result in traffic congestion and longer routes and, thus, impose inconvenience to travelers and significant cost 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 the two-lane loading case.

The two-way shear equation in ACI 440.11 was originally developed nearly two decades ago using experimental data from early FRP materials, most of which are no longer representative of modern GFRP reinforcement. With current GFRP bars exhibiting significantly improved mechanical and surface properties, the validity of the existing equation requires reassessment to ensure practical and economical design. This study evaluates the ACI 440.11 two-way shear provisions using a comprehensive database of 49 GFRP-RC interior slabs and 14 edge column connections. The current code equation was found to be highly conservative, yielding an average test-to-predicted ratio of 2.13. Updated equations are proposed for both interior and edge conditions, reducing the ratio to 1.02 and 1.04, respectively, while maintaining acceptable statistical variation. Additionally, symbolic regression (SR) is used to develop machine-learning-based expressions, which show high predictive accuracy. The proposed models provide reliable, physically grounded, and less conservative predictions of punching shear capacity, supporting broader implementation of GFRP reinforcement in structural concrete applications.

The determination of the static coefficient of friction between steel and concrete is essential for the design and safety of structures, particularly in systems operating under low axial stresses, such as foundation slabs supporting waste storage casks. In such applications, sliding resistance and shear transfer at the steel–concrete interface play a critical role in ensuring stability and overall structural performance. Inadequate friction at this interface can lead to sliding, reducing the structure’s capacity to resist lateral forces and potentially resulting in serviceability or safety concerns. This study presents an innovative approach to evaluate the static coefficient of friction between steel, prepared to a specific steel surface roughness level (SSPC-SP 6), and concrete with varying surface roughness profiles, including light sandblast, light-to-medium sandblast, medium bush hammer, and heavy sandblast finishes. Tests were performed under low normal stresses (18, 33, and 50 kPa) and shear displacement rates (3, 5, 7, and 9 mm/s). A custom test setup was developed to apply controlled displacement to a concrete block while measuring the horizontal force required to initiate sliding against the steel plate. The results indicate that the static coefficient of friction across all concrete surface roughness levels ranges from 0.68 to 0.75, with a mean value of 0.72. Statistical analysis at a 95% confidence level reveals that variations in concrete surface roughness, shear displacement rates, and applied normal stresses do not produce significant differences in the static coefficient of friction. Consequently, utilizing concrete with light sandblast surface preparation in the field is sufficient to achieve a static coefficient of friction comparable to aggressive surface roughness profiles. These findings simplify construction practices while ensuring reliable shear transfer and sliding resistance at steel-concrete interfaces in low axial stress applications.

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (i.e., a combination of bonded and unbonded (steel and/or carbon fiber reinforced polymer (CFRP)) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in the ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI PRC-440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provisions address the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the Modified Deformation-Based Approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without non-prestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI PRC-440 stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-to-depth ratio, as well as loading applications.