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.

Current design assumptions for precast, prestressed concrete piles embedded in cast-in-place (CIP) pile caps or footings vary across states, leading to inconsistencies in engineering practices. Previous studies suggest that short embedment lengths (0.5 to 1.0 times the pile diameter) can develop approximately 60% of the bending capacity of the pile, with full fixity potentially achieved at shorter embedment lengths than current design specifications due to confinement stresses. This study experimentally evaluates 10 full-scale pile-to-cap connection specimens with varying embedment lengths, aiming to investigate the required development length for full bending capacity. The findings demonstrate that full bending capacity can be achieved at the pile-to-pile cap connection with shallower embedment than code provisions, challenging existing design standards and highlighting the need for more accurate guidelines for bridge foundation design.

Laboratory tests of deep, lightly reinforced concrete members without shear reinforcement demonstrate that the nominal shear stress at failure decreases with increasing depth and with decreasing tension longitudinal reinforcement ratio. Design procedures for one-way shear strength in ACI 318-19 incorporate these effects, but result in relatively low design shear strengths for members with both large depth and low reinforcement ratio. To better understand the effects of depth and longitudinal reinforcement on shear strength, tests were conducted on beams with varying depth, a relatively low ratio of high-strength longitudinal reinforcement, and with either no shear reinforcement or minimum shear reinforcement. Loads were applied slowly and monotonically and included concentrated loads plus self-weight. Beam supports were either point supports, as in a beam, or uniformly distributed, similar to some foundation reactions. The test results demonstrate size and longitudinal reinforcement effects and suggest that a lower-bound unit shear strength may be applicable for the design of members with both large depth and low reinforcement ratio.

This research aims to provide a theoretical foundation for the structural design of magnesium phosphate cement (MPC) in high-temperature environments and facilitate the recycling of municipal solid waste incineration bottom ash (BA). Uniaxial compression tests of BA–MPC after exposure to temperatures from 20°C to 1000°C were carried out. Subsequently, the stress-strain curve, peak stress, peak strain, and deformation modulus are examined. The peak stress, peak strain, and deformation modulus, considering the influence of temperature factors, are proposed using regression analysis. Based on the continuum damage mechanics, the axial compression damage constitutive model of MPC is developed, accompanied by an analysis of its temperature damage characteristics. The results show that BA improves MPC strength and helps stabilize its deformation after exposure to high temperatures. The peak stress of MPC decreases after exposure to high temperatures, and the peak stress of BA–MPC is higher at the same temperature. At 1000°C, the peak stress of MPC ranges between 15.86 MPa and 28.38 MPa. After high thermal exposure, the peak strain fluctuation of the MPC with BA stays small, and the deformation modulus is higher than that of the MPC without BA. The developed MPC axial compression damage constitutive model can accurately describe the stress-strain relationship of MPC under axial compression following high-temperature exposure, with a correlation coefficient greater than 0.86. The temperature damage variable of MPC rapidly accumulates in the range of 20°C to 200°C. At 600°C, the temperature damage variable and the total damage variable without BA attained the maximum values of 0.656 and 0.751, respectively. BA can reduce the total damage and temperature damage of MPC to a certain extent.

Steel columns are commonly attached to concrete foundations with groups of cast-in-place headed anchors. Recent physical tests and simulations have shown that the strength of these connections can be limited by concrete breakout failure. Four full-scale physical specimens of axially loaded columns attached to a foundation slab were tested, varying the shear reinforcement configuration in the slab. All specimens were governed by concrete breakout failure. The tests suggest that adequately placed distributed shear reinforcement can increase connection strength and displacement capacity. Steep cone failures were observed to limit the beneficial effect of shear reinforcement. Calibrated finite element models were used to investigate critical parameters such as the extent of the shear-reinforced region and bar spacing. A design approach is proposed to calculate connection strength by adding the strength of the concrete and the distributed shear reinforcement. Design detailing is discussed.