International Concrete Abstracts Portal

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.

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.

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.

The challenges of deterioration and increasing maintenance costs in steel-reinforced concrete railway sleepers emphasize the urgent need for innovative, durable, and sustainable alternatives. This study evaluated the shear strength of precast concrete sleepers prestressed with basalt fiber-reinforced polymer (BFRP) rods, using normal self-consolidating concrete (NSCC) and fiber-reinforced self-consolidating concrete (FSCC). Seven full-scale specimens, each 2590 mm (8 ft, 6 in.) in length and prestressed to 30% of the tensile strength of BFRP rods in accordance with the Canadian Highway Bridge Design Code (CHBDC), were tested to assess cracking loads, ultimate strength, bond behavior, and failure mechanisms. All tests were conducted in accordance with the American Railway Engineering and Maintenance-of-Way Association (AREMA) guidelines. The results indicate that all specimens met AREMA design load requirements without visible cracks or slippage based on a train speed of 64 km/h (40 mph), annual traffic of 40 MGT (million gross tons), and sleeper spacing of 610 mm (24 in.). Comparative analysis using CSA S806-12 (R2021) design standard and ACI 440.4R-04 (R2011) design guide revealed that predictions based on CSA S806-12 (R2021) were less conservative than those from ACI 440.4R-04 (R2011) for the shear strength of BFRP prestressed sleepers. The BFRP rods exhibited excellent tensile performance, with minimal prestress losses, and their sand-coated surface ensured efficient load transfer by preventing slippage and enhancing the bond strength. FSCC specimens demonstrated delayed cracking, enhanced crack control, and ductility compared to NSCC specimens. These findings highlight the potential of BFRP prestressed concrete sleepers, particularly when combined with FSCC, as a sustainable solution for railway infrastructure, emphasizing the need for a design code refinement for BFRP applications.

Crack densities obtained from on-site surveys of 74 bridge deck placements containing concrete mixtures with paste contents between 22.8% and 29.4% are evaluated. Twenty of the placements were constructed with a crack-reducing technology (shrinkage-reducing admixtures, internal curing, or fiber reinforcement) and 54 without; three of the decks with fiber reinforcement and nine of the decks without crack-reducing technologies involved poor construction practices. The results indicate that using a concrete mixture with a low paste content is the most effective way to reduce bridge deck cracking. Bridge decks with paste contents exceeding 27.3% had a significantly higher crack density than decks with lower paste contents. Crack-reducing technologies can play a role in reducing cracking in bridge decks, but they must be used in conjunction with a low paste content concrete and good construction practices to achieve minimal cracking in a deck. Failure to follow proper procedures to consolidate, finish, or cure concrete will result in bridge decks that exhibit increased cracking, even when low paste contents are used.