International Concrete Abstracts Portal

In practical engineering, beams requiring strengthening were usually preloaded; research on their strengthening techniques directly affected structural safety and cost-effectiveness. This study investigated the flexural behavior of preloaded RC beams strengthened with prestressed carbon textile reinforced concrete (CTRC) plates using four-point bending tests. Parameters included preload levels and whether to unload during strengthening. Results showed that strengthening with prestressed CTRC plates effectively improved the service moment, ultimate bending moment, and crack resistance, and preload level and whether to unload during strengthening had no significant effect on the strengthening effect. All strengthened beams failed due to the CTRC plate rupturing, with post-failure moments reducing to the unstrengthened beam's ultimate moment level. Pre-cracking flexural stiffness decreased with increasing preload, and the stiffness after cracking was independent of the preload and strengthening method. Finally, the ultimate bending moments were evaluated using four current codes, with the Chinese code exhibiting the highest prediction accuracy.

This paper presents the behavior of anchorage zones, also known as end zones, with discrete reinforcing bars and continuous meshes. To examine the implications of various reinforcing schemes on the capacity, cracking, and failure of end zones, 50 block specimens are loaded, and their responses are analyzed. Test parameters include the types of reinforcing bar materials (steel and glass fiber-reinforced polymer, (GFRP)) and the configurations of the reinforcing bars and steel meshes (single and multiple placements). In terms of load-carrying capacity, the specimens embedded with the GFRP rebars outperform those with the steel reinforcing bars and meshes by 14.0%. The post-peak load drop of the blocks with the steel and GFRP reinforcing bars is analogous due to distributed axial stresses in the unreinforced concrete region, differing from the abrupt drop observed in the specimens with the steel meshes that intersect the concrete in orthogonal directions. While concrete splitting originates from local tension generated near the axial compression, the location of cracking is dominated by the path of stress trajectories related to the number of reinforcing bars, which is not recognized in the case of the meshed specimens. The pattern of the isostatic lines of compression clarifies the development of bursting forces that cause cracking in the concrete. A two-stage analytical model is formulated to predict the magnitude of bursting forces and determine the effects of several parameters on the response of the end zones. The applicability of existing design expressions is assessed, and the need for follow-up research is delineated.

Precast concrete hollow-core floor units have been shown to sustain cracking in their unreinforced webs near the end support during earthquakes. Post-cracking shear strength is essential to maintain gravity loads following earthquakes. This paper presents the results of an experimental program that examined the post-cracking shear capacity of twelve full-scale hollow-core floor units. Variables included different support seating lengths, shear span-to-depth ratios, and loading protocols. Results showed that cracking in the unreinforced webs of hollow-core floor units can reduce shear capacity by at least 60% relative to uncracked strength. Additionally, reduced support seating length markedly decreased post-cracking shear strength, with 30 mm seating providing no residual capacity, while 50 and 100 mm lengths retained approximately 50 and 100% of the uncracked section capacity, respectively. The findings from this study provide a basis to quantify the residual capacity of web-cracked hollow-core floor units, which can be used in post-earthquake structural assessments.

The term “mass concrete” characterizes a specific concrete condition that typically requires unique considerations to mitigate extreme temperature effects on a structure. Mass concrete has historically been defined by the physical dimensions of a massive concrete element with the intent of identifying when differential temperatures may induce early-onset cracking, leading to reduced service life. More recently, in addition to differential temperature considerations, extreme upper temperature limits have been imposed by the American Concrete Institute to prevent long-term concrete degradation. Studies dating back to 2007 show that shafts as small as 48 in. (1.2 m) in diameter can exceed both differential and peak temperature limits; in 2020, augered cast-in-place piles as small as 30 in. (0.76 m) in diameter exceeded one or both limits. This suggests the term “mass concrete” is misleading when considering today’s high-early-strength or high-performance mixture designs. This study applies numerical modeling coupled with field measurements to investigate the effects of concrete mixture design, drilled shaft diameter, and environmental conditions on heat energy production and temperature. Further, the outcome of this study focuses on developing criteria that combine the effects of both size and cementitious material content to determine whether unsafe temperature conditions may arise for a given drilled shaft design.

Reinforced concrete (RC) members undergoing shrinkage are susceptible to cracking when restrained; however, studies on this behavior are limited. Thus, the main objective of this paper is to present crack-widths, crack-patterns, and shrinkage strains from an experimental study on three RC walls with aspect ratios of 3.26 and 1.08, and horizontal reinforcement ratios of 0.2% and 0.35%, as well as a rectangular tank with 0.24% reinforcement. A 3-D nonlinear finite element (FE) analysis is conducted, and the results reveal that although the model predicts strains and maximum crack-widths reasonably well, the crack-pattern differs from the experiments. The possible reasons for this difference are discussed, and a parametric study is done to propose design equations to estimate restraint factors along the wall centerline for different aspect ratios. These equations can be used to estimate the cracking potential in the design stage without the need for a nonlinear FE analysis. For L/h above four, horizontal reinforcement has a negligible effect on the restraint, and for L/h above eight, full-height cracks can be expected due to almost uniform restraint. Finally, the design codes are compared, and it is found that ACI 207.2R-07 and CIRIA C766 predict shrinkage-induced crack-widths conservatively and reasonably accurately.