International Concrete Abstracts Portal

This paper presents the interface shear between ordinary concrete and ultra-high-performance concrete (UHPC) connected with glass fiber-reinforced polymer (GFRP) reinforcing bars. Following ancillary tests on reinforcing bar fracture under in-plane shear loading, concrete-reinforcing bar assemblies are loaded to examine capacities and failure modes as influenced by the size, spacing, and number of the reinforcing bars. While the shear behavior of bare reinforcing bars is primarily governed by the orientation of the load-resisting axes in the glass fibers and their volume, the size and spacing of the reinforcement largely control the interface capacity by affecting the load-transfer mechanism from the reinforcing bar to the concrete. The degree of stress distribution affects the load-displacement response of the interface, which is characterized in terms of quasi-steady, kinetic, and failure regions. The primary failure modes of the interface comprise rebar rupture and concrete splitting. The formation of cracks between the ordinary concrete and UHPC results from interfacial deformations, leading to spalling damage when applied loads exceed service levels. An analytical model is formulated alongside an optimization technique. The capacities of the interface in relation to the reinforcing bar rupture and concrete splitting failure modes are predicted. Furthermore, a machine learning algorithm is used to define a failure envelope and propose practice guidelines through parametric investigations.

The ACI CODE-318-19 provisions for one-way shear strength (V_c) in reinforced concrete (RC) members were majorly modified for the first time since 1963. ACI CODE-318-19 equation addresses certain previously identified limitations of the well-known V_c= 0.17λ√f_c′b_wd equation for members without shear steel reinforcement, incorporating factors such as size effect and the influence of longitudinal reinforcement ratio. This study takes a multi-metric approach to evaluate the accuracy and safety of ACI CODE-318-19’s one-way shear relationship for RC members without stirrups. ACI CODE-318-19 predictions are compared against those of its predecessor and other state-of-the-art models, using a database of experimental results gathered by joint ACI-ASCE Committee 445 and DAfStb. This study shows that the ACI CODE-318-19 equation significantly improved accuracy and safety over the ACI CODE-318-14 provisions. One-way shear predictions of ACI CODE-318-19 for RC members without shear reinforcement are generally comparable to existing models, though certain aspects may benefit from continued development and refinement.

Accelerated carbonation treatment is recognized as an effective method for enhancing recycled aggregates (RA), but its potential in structural concrete, particularly with respect to seismic performance, remains underexplored. To address this gap, this study is the first to integrate mesoscale modeling with structural finite element analysis (FEA) to systematically investigate the seismic behavior of carbonated recycled aggregate concrete (CRAC) shear walls under dynamic loading. At the material scale, uniaxial compression tests on CRAC cylindrical specimens with varying replacement ratios were conducted to evaluate their stress–strain behavior and mechanical properties. A mesoscale model of CRAC was developed using a random aggregate placement method, and FEA was employed to extend the analysis of replacement ratios. At the structural scale, a CRAC shear wall FEA model was established, incorporating the material-level stress–strain relationships into cyclic lateral loading simulations. Parametric analysis revealed that increasing both the axial load ratio and the replacement ratio significantly reduced the seismic performance of CRAC shear walls, with a maximum reduction of 21.7%. Based on these findings, recommended ranges for RA replacement ratios and axial load ratios are proposed, providing practical guidance for the structural application of CRAC.

In this study, the behavior of diaphragm-to-wall connections with collector reinforcement and construction joints was investigated. Four slab-to-wall connection specimens were tested under cyclic loading. Diaphragm connection details, such as shear friction reinforcement (i.e., slab dowel bars anchored by 90-degree hooks within the wall) and the use of spandrel beams as collectors, were considered as test variables. When fabricating the specimens, concrete was consecutively cast for the wall and slab, and construction joints were placed on the sides of the wall and spandrel beams. The tests showed that the diaphragm connections exhibited the typical ductile behavior characterized by the robust initial stiffness and subsequent post-yield plastic behavior. Before concrete failure on the front of the wall, the load transfer from the diaphragm to the wall was governed by a nodal zone action; then, the subsequent connection behavior was dominated by shear friction as sliding failure occurred on the side of the wall along the slab construction joints. The diaphragm-to-wall connection strengths were evaluated using the strut-and-tie model and shear friction theory. The calculated strengths were in good agreement with the test strengths. Based on the investigation results, design considerations of the diaphragm-to-wall connection were proposed.

This study investigated the shear bond behavior, with and without optimized interfaces, between conventional and geopolymer steel fiber–reinforced concretes. Sixteen prismatic and eight cylindrical composite specimens were cast with interface inclination angles of 45° and 27°, respectively. In prisms, the inclined interface area was varied: eight were optimized by 50% to balance compressive and shear stresses, allowing a more accurate determination of cohesion and friction coefficients under steel fiber effects. Fiber volume fractions of 0.0, 0.5, 1.0, and 1.5% were tested, and the influence of epoxy at the interface was also assessed. Optimized prisms exhibited adhesive failure along the interface, matching the internal friction angle, whereas non-optimized prisms showed cohesive failure with a friction angle deviating from the interface. Increasing fiber content improved performance, especially when combined with epoxy. A new bond shear strength model is proposed, incorporating friction, cohesion, and fiber effects.