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.

Slender reinforced concrete columns have been employed as components of telecommunication and internet infrastructure since the deployment of the system more than 30 years ago. The assessment of these structures must consider the time dependent behavior of concrete. In this context, a numerical investigation is conducted to determine the critical buckling load and the stress distribution in sections subject to creep and shrinkage of concrete. The guidelines used are those from the American Concrete Institute. It is concluded that the maximum stress induced in the reinforcement is 1.14% of the steel yield stress. Therefore, no yielding of the reinforcement is registered to the examined case which ensures safety against permanent deformation. During the elapsed time of 7500 days, the modulus of elasticity of concrete decreased by 53% and the critical buckling load 40%. The results obtained can be applied to similar cases through the slenderness index and the reinforcement ratio.

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.

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.

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.