International Concrete Abstracts Portal

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.

Progressive collapse behavior of reinforced concrete frame buildings has been studied extensively, but most of the research has concentrated on frames containing seismic details. This paper presents results from analyses of the progressive collapse behavior of reinforced concrete frame buildings containing details used in regions of low seismicity following ACI CODE-318-19. The analytical simulations presented in this paper include the effect of moment redistribution that occurs after plastic moments are reached at sections of maximum moment. Ten-story 3-D frame models were designed in accordance with ACI CODE-318-19 and analyzed under progressive collapse scenarios involving the non-simultaneous removal of an interior and a corner perimeter column following ASCE 76-23. Nonlinear material behavior in these analytical models was captured using a lumped plasticity approach using hinge properties calibrated using results from laboratory experiments of full-scale sub-assemblages representing a portion of the perimeter frame containing details corresponding to non-seismic zones. The effect of catenary action in beams after column removal was included in the analyses, and the potential for premature shear failure of beams was assessed. Furthermore, models were also constructed to investigate the beneficial effects of increased rotational capacity of perimeter beams that result from using closer stirrup spacing at beam ends. This study demonstrates the importance of incorporating properly detailed continuous longitudinal bars enclosed within closely spaced closed stirrups at ends of beams of reinforced concrete frames in non-seismic zones to provide progressive collapse resistance. The study also highlights the importance of considering three-dimensional effects in models of frames to account for out-of-plane moment redistribution after loss of supporting elements.

In the Netherlands, the 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 of these experiments can be used for the assessment of existing skewed slab bridges.

To promote the application of fiber-reinforced polymer (FRP) bars reinforced ultra-high-performance seawater sea-sand concrete (FRP-UHPSSC) structures in marine construction, four-point static bending tests were carried out on 16 FRP-UHPSSC beams with different reinforcement ratios, height of cross-section, and type of FRP bars to investigate the ultimate load-carrying capacity, the midspan deflection, and the failure modes of the beams. The experimental results show that all the test beams are brittle failures, and the failure mode of the beams is shear failure when the ratio of the actual reinforcement ratio to the balanced one is higher than 2.73. Increasing the reinforcement ratio and the beam section height both improve the bending moment at ultimate load and the flexural stiffness at the service limit state. The Steel-FRP composite bars (SFCB) reinforced UHPSSC beams have the maximal bending moment at ultimate load, and the basalt fiber reinforced polymer (BFRP) bar reinforced UHPSSC beams have the optimal ductility. The deviation of ultimate bending moment and midspan deflection obtained by the proposed calculation method is reduced from 7.5 to 2.8%, and from 15 to 3%, respectively, compared with current specifications for FRP-reinforced concrete structures.