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Structural members made of ultra-high-performance concrete (UHPC) have been attractive to engineers and researchers due to their superior mechanical properties and durability. However, existing studies were focused on the behavior of UHPC members reinforced with micro straight steel fibers at a volume fraction between 1 and 3%. There is a lack of studies on the influence of different types and amounts of fibers on the shear behavior of UHPC structural members. The objective of the study was to experimentally investigate the shear behavior of UHPC beams with macro hooked-end steel (MHS) fibers and polyvinyl alcohol (PVA) fibers, which are two of the most used fibers for high-performance fiber-reinforced cementitious composites. The shear behavior of ten large-scale non-prestressed UHPC beams was studied. The experimental parameters included the shear span-to-effective depth ratio, the fiber volume fraction, and the type of fibers. It was found that both MHS fibers and PVA fibers were effective in enhancing the shear performance of the UHPC beams whether the shear transfer mechanism was governed by arch action or beam action. Moreover, the measurement results of the average crack spacing imply the distinct difference in the fiber bridging effects of the MHS fibers and PVA fibers in the UHPC beams.

The shear stirrups and bend-up reinforcement in ultra-high-performance concrete (UHPC) beams could potentially be excluded due to the superior mechanical properties of UHPC. This paper reports the new findings of an experimental research into the factors that influence the shear behavior of non-stirrup UHPC beams. Fourteen beams were tested in shear, comprising twelve non-stirrup UHPC beams and two normal concrete (NC) beams reinforced with stirrups. The test variables included the steel fiber volume content (2.0%, 1.5%, and 0%), the shear span-to-effective-depth ratio (1.2, 1.8, 2.0, and 3.1), beam width (150 mm and 200 mm), and beam height (300 mm, 350 mm, and 400 mm). The results demonstrated that the steel fiber volume content had a significant influence on the shear behavior of the non-stirrup UHPC beams. The failure modes of the beams without steel fibers were typically brittle, whereas those reinforced with steel fibers exhibited ductile failure. The shear resistance of the beams could be significantly enhanced by the addition of steel fibers in the concrete mix. Furthermore, the post-cracking load-bearing performance of the beams could also be markedly improved by the addition of steel fibers. In addition, the shear span-to-effective-depth ratio had a considerable impact on the failure mode and the ultimate shear strength of the tested beams. The contribution of steel fibers to the shear capacity of the UHPC beams was observed to increase as the shear span-to-effective-depth ratio increased. The French standard formulae tended to overestimate the contribution of steel fibers, and the calculation results were found to be more accurate for UHPC beams with a moderate shear span-to-effective-depth ratio (around 2.0). Moreover, the French standard formulae demonstrated greater accuracy at a larger beam height for calculating the contribution of UHPC matrix.

The shear span-to-effective depth ratio (a/d) is one of the factors governing the shear behavior of reinforced concrete (RC) beams, with or without shear reinforcement. In high-strength concrete (HSC), cracks may propagate between the aggregate particles and result in a brittle failure which is against the philosophy of most design guidelines. The experimental results of six HSC beams, with and without shear reinforcement, tested under four-point bending with a/d ranged from 2.0 to 3.0 are presented and compared with different model equations in design codes. The a/d ratio has higher influence on the shear strength of reinforced HSC beams without shear reinforcement than beams with shear reinforcement. Most of the shear resistance prediction models underestimate the concrete shear strength of the beams but overpredict shear resistance of beams with shear reinforcement. However, the fib Model code 2010 accurately predicted the shear resistance for all the beams within an appropriate level of approximation (LoA).

Geopolymer concrete (GPC) has emerged as a sustainable alternative to ordinary Portland cement concrete (OPCC) as GPC significantly reduces embodied carbon dioxide emissions. This study compared the shear behavior of reinforced OPCC beams and GPC beams of the same cross-section and compressive strength. The study tested nine beams under three-point bending to evaluate the effects of concrete type and shear span on the shear strength. The results showed that OPCC and GPC beams exhibited relatively similar reduction rates in the shear strength with increasing a/d ratios, while the failure mode shifted from shear in OPCC beams to shear-flexure in GPC beams. The maximum deflection of GPC beams significantly increased with increasing a/d ratios. Moreover, empirical shear strength equations, intended for OPCC beams in various design codes, underestimated the shear strength of GPC beams by about 11.0-26.9% at the a/d ratio of 4.3 but significantly underestimated the shear strengths of GPC beams by 77% at lower a/d ratios of 1.6 and 2.9. Therefore, modifications are proposed to the existing design OPCC shear strength equations to significantly improve the prediction accuracy for the shear strength of GPC beams.

This paper suggests a new perspective on reinforcement details for concrete corbels, whereby the familiar approach of secondary distributed reinforcement is substituted with modeling the corbel as a strut-and-tie system, in agreement with ACI 318 on strut-and-tie modeling (STM). The study consists of constructing and testing 15 corbel specimens until failure, including six conventionally reinforced reference specimens and nine proposed specimens in which only struts and ties were reinforced. The shear span-effective depth ratio (a/d) is variable: 0.5, 1, and 1.5, respectively. The test results show crack and strain evolution in both concrete and steel bars, together with load-deflection response. Conclusions show that corbel designs based on a strut-and-tie system provide substantial saving in weight of approximately 13 to 52% along with a less obvious but still substantial extra ultimate capacity of 12 to 50% compared to the nominal ACI 318-14 STM design load. Keywords: corbel; proposed specimens; reinforced concrete; shear span-effective depth ratio; strut-and-tie model.

Various concretes have been developed to meet the principles of sustainability. High volume fly ash-self compacting concrete (HVFA-SCC) is one example. The utilization of HVFA-SCC for structural applications, however, raises a concern among designers: that HVFA-SCC may not be as strong as conventional concrete when carrying shear forces. This concern is related to slow strength development and relatively smoother crack surface formation in HVFA-SCC, which, consequently, reduces the aggregate interlock mechanism contribution to the shear strength. In this respect, the design code for estimating the shear strength of HVFA-SCC may not be valid for the reason that the code was developed on the basis of the conventional concrete database. Previous research on the shear strength of HVFA-SCC was limited and no database can be extracted to justify the validity of the shear design code. This research was conducted to clarify the suitability of shear design code for HVFA-SCC. The research began with a limited laboratory investigation, followed by a numerical investigation to expand the range of results. Two types of HVFA-SCC beams with dimensions of 100 mm × 150 mm × 1700 mm were prepared, utilizing 50% and 60% fly ash. The shear behavior obtained from the laboratory investigations was then numerically modeled with the help of 3D ATENA Engineering software. The numerical model was used to explore the influence of reinforcement ratio, shear span to beam effective depth ratio, and beam size on the shear strength of the HVFA-SCC beam. The results were compared with the shear strength database of conventional and unconventional concrete beams to judge if the provisions in the design code can be applied to the shear design of an HVFA-SCC beam. The results confirm that the ACI shear design code is applicable for HVFA-SCC.