International Concrete Abstracts Portal

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.

This paper describes an integrated experimental and numerical investigation on the behavior of lapped, grouted connections for modularized construction of safety-related nuclear reinforced concrete (RC) shear wall structures. The novel lapped geometry of the proposed connection provides “face-to-face” (rather than “end-to-end” or “butt”) joint interfaces with large grouted construction tolerances and large surfaces to develop the required continuity of the strength and stiffness of the wall. A total of 5 modular beam specimens and one state-of-practice (monolithic) beam specimen were tested under 3-point simply supported monotonic loading conditions. These beam specimens represented horizontal slices taken out of the length of a nuclear shear wall structure. Continuum finite element analyses were conducted to compare with the experimental test results and to develop information regarding the effects of material differences between the specimens. The experimental and numerical results showed that adequate clamping of the connection, as well as additional longitudinal beam reinforcement on both sides of the grout joint, are necessary to achieve the desired “strong” connection behavior with full strength and stiffness continuity between adjacent RC modules.

This study presents the development of a novel three-dimensional (3-D) assembled retaining wall block system, in which individual blocks are interconnected in the upper-lower, left-right, and front-back directions. Unlike conventional segmental block gravity walls that rely solely on horizontal shear keys between upper and lower blocks, the proposed 3-D system is designed to resist shear forces across the entire block cross-section through comprehensive mechanical interlocking. To evaluate its structural performance, direct shear tests were conducted, focusing on two key parameters: the block arrangement between the front and back sides, and the frictional resistance between the block and the foundation concrete. Experimental results demonstrated that the proposed system exhibits significantly enhanced shear strength compared to conventional retaining wall systems. Based on these findings, shear strength estimation formulas were developed to support structural design and stability assessment. The proposed 3-D block system not only improves the mechanical integrity of retaining walls but also holds potential for enhanced resilience against complex geotechnical challenges due to climate change. These results suggest that the new system provides a reliable and robust alternative for the design of segmental retaining walls requiring high shear resistance and long-term stability.

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.

Concentrated shear deformation near the base of a squat wall, referred to herein as sliding shear, is one of the major mechanisms that can limit the strength and deformation capacity of reinforced concrete (RC) low-rise or squat walls. This paper reports tests of five large-scale RC squat wall specimens without axial load to investigate the effects of (1) longitudinal reinforcement layout, (2) shear stress demand, (3) high-strength materials, and (4) aspect ratio on the sliding shear behavior of squat walls. All specimens were tested under lateral displacement reversals. Test results indicate that the maximum strength of all test specimens with an aspect ratio of 0.5 was primarily associated with, or limited by, sliding shear at the wall base. For specimens with an aspect ratio of 0.5 and negligible axial load, the presence of special boundary elements did not have an apparent influence on wall behavior. Increasing the amount of longitudinal reinforcement, which also increased wall strength, resulted in less sliding deformation before 1.0% drift ratio. Beyond 1.0% drift ratio, all specimens with an aspect ratio of 0.5 exhibited a substantial pinching of the hysteretic response, where sliding along the wall base accounted for 80% of the overall deformation. Specimens with high-strength materials exhibited less deformation capacity than other specimens due to bar fracture at the wall base. As the aspect ratio increased to 1.0, the relative contribution of sliding deformation to overall drift decreased substantially to less than 20% of overall deformation. Based on the response characteristics of the test specimens, a sliding shear strength model for walls with negligible axial load is proposed. A database consisting of test results from fifty-five specimens (including five from this study) was developed to verify the proposed strength model.