International Concrete Abstracts Portal

In this study, a detailed innovative procedure is devised to recover the full response of reinforced concrete deep beams using an improved strut-and-tie method based on ACI 318 rules. The load-deflection curve is described by two critical response levels represented by the yielding and ultimate points. The strut and tie method (STM) is used to determine the nodal displacements under a unit load and compute the yielding and ultimate load in the strut-and-tie model as the minimum force needed to realize each loading stage from all truss elements. Once the critical load at the two stages is determined, the elongation, strain, and stress of each element in the truss are extracted, thus avoiding the need to approximate the nonlinear strain profile across the depth. Also, two solution strategies using the secant and tangent stiffness are formulated, and their results are successfully compared to the experimental response of seven deep beams with a wide range of shear span-to-depth ratios. The failure modes reported experimentally perfectly match the failure member indicated by this improved analysis.

This study evaluates the seismic performance of circular columns reinforced with fiber-reinforced polymer (FRP) bars, focusing on the efficacy of existing code provisions (ACI CODE-318-19, CSA A23.3-24, CSA S806-12, CSA S6-25) in predicting drift and moment capacities. A database of 38 full-scale columns tested under lateral cyclic loading with varying axial load levels, spiral pitches, and reinforcement types (GFRP/steel longitudinal bars) was analyzed to assess code provisions, confinement effectiveness, and strength enhancements. Results demonstrate that CSA S6-25, which incorporates updated FRP compressive strain limits (0.008E_f for spirals), outperformed other codes, aligning with about 85% of experimental data in ideal performance quadrants. Close spiral pitch (≤ 75 mm [2.95 in.]) and low axial loads were critical to achieving drift ratios ≥3% and moment capacity ratios (M_max/M_o) exceeding 2.0. Replacing steel spirals with GFRP spirals did not result in substantial variation in the seismic performance of columns. Columns with GFRP longitudinal bars exhibited comparable ductility and observed a substantial increase in moment capacity (M_max) compared to unconfined nominal moment capacity (M_o) due to delayed bar buckling under effective confinement. However, columns with GFRP longitudinal bars observed a softer response, and the determination of probable moment to calculate the shear demand still remains questionable and requires more analytical investigations.

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.