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Failure in beams reinforced with a small amount of transverse reinforcement is brittle due to reinforcement rupture after critical shear cracking occurs. To eliminate this problem, standards recommend formulas to calculate the minimum amount of transverse reinforcement in reinforced concrete structures. Reinforcement can resist loads after the first crack’s appearance, preventing beam rupture from being brittle but making it somewhat ductile. This paper presents a theoretical experimental analysis to determine the minimum transverse reinforcement ratio in beams of high-strength ordinary portland cement concrete (BHSOPCC), low-strength ordinary portland cement concrete (BLSOPCC), and low-strength geopolymeric concrete (BLSGC). The beam dimensions were 150 x 450 x 4500 mm. They were subjected to a four-point bending test to assess shear failure. The transverse reinforcement ρsw,minfyk ranged from 0 to 1.16 MPa, in the ranges provided by ACI 318-19, AASHTO LRFD, fib Model Code, and ABNT NBR 6118:2014. This paper investigates the minimum shear reinforcement ratio for various types of concretes with different strengths and attempts to reevaluate the associated standards that have already been established. The parameter τwy*/τwcr proposed in this paper to define whether or not a beam has minimum transverse reinforcement is more appropriate.

ACI 318-19 requires that prestressed concrete hollow-core slabswith depths exceeding 12.5 in. (320 mm) and subjected to a factored shear greater than half the design web-cracking shear strength be provided with at least minimum shear reinforcement. Because the use of bar-type shear reinforcement in hollow-core slabs is generally not possible, this requirement limits the use of these members in shear-critical cases. In this research, the use of hooked steelfibers as a means to increase the shear strength of deep hollowcore slabs was evaluated through 14 tests on extruded hollow-core slabs. Slab thickness was 16 in. (406 mm) and the shear span-effective depth ratio (a/d) was either 3.0 or 3.5. Two types of hooked steel fibers were evaluated at dosages between 40 and 62 lb/yd3 (24 and 37 kg/m3). Type 1 fibers had a single hook at each end and Type 2 fibers had double hooks at each end. The fiber-reinforced concrete slabs exhibited peak shear strengths that ranged between 0.94 and 1.29 times the ACI 318-19 calculated web-cracking shear strength Vcw, while the two slabs without fibers failed at shear forces corresponding to 0.93 and 0.87Vcw. Besides an increase in shear strength, the presence of fibers, particularly Type 2 fibers, led to a more gradual post-peak strength decay. Failure of the hollowcoreslabs without fibers occurred as soon as one web exhibitedweb-shear cracking. In the hollow-core slabs with fibers, on theother hand, fibers bridging the first web-shear crack preventedthis web from experiencing a sudden loss of shear capacity, which allowed the slabs to sustain additional shear until multiple webs had cracked in shear.

A database of interface shear-transfer experiments on uncracked reinforced concrete specimens was created from published test results. A total of 774 tests were reviewed, with data coming from tests conducted between 1969 and 2014. Once compiled, the database was used to evaluate the accuracy of the interface shear transfer provisions from the AASHTO LRFD Bridge Design Specifications, Eurocode 2, and CSA A23.3. Through this evaluation, it was determined that experimental capacities were an average of 1.49, 1.93, and 2.83 times greater than the code-calculated nominal capacities for the LRFD, Eurocode, and CSA codes, respectively. While each of the codes was conservative on average, the degree of conservatism was found to be dependent on design variables such as concrete compressive strength, amount of interface reinforcement, and member size. For example, conservatism of LRFD was lowest for specimens having concrete compressive strengths less than 60 MPa (87 ksi). Conditions associated with the lowest degrees of conservatism are identified and discussed.

An experimental study was performed to examine current code requirements for minimum web reinforcement of reinforced concrete deep beams. Twelve full-scale tests were conducted in which the shear span-depth ratio (a/d) was 1.2, 1.85, or 2.5. At each a/d, the quantity of web reinforcement was the primary variable. Web reinforcement ranged from 0 to 0.3% in the vertical and horizontal directions. The compressive strength of concrete of the test specimens ranged from 3200 to 5000 psi (22 to 34 MPa). Diagonal cracking loads, diagonal crack widths, and failure shears were recorded for each test. The results indicated that a larger quantity of web reinforcement was needed to adequately restrain the width of diagonal cracks than to provide adequate deep beam shear capacity. Based on the strength and serviceability results, a minimum web reinforcement of 0.3% in each orthogonal direction was recommended for deep beams.

Concrete in a triaxial state of stress can withstand larger stresses and deformations than the same concrete in its unrestrained state. Wrapping concrete columns with wire under tension induces an active triaxial state of stress in the concrete, increasing its load-carrying capacity. An experimental investigation was carried out to evaluate the effects of load eccentricity, slenderness ratio, and initial lateral prestress on load capacity. Tests were carried out on 6-in. (150-mm) diameter columns with slenderness ratios of 16, 24, 36, and 48; loads were applied at eccentricities e/D of 0, 0.1, 0.25, and 0.5. Initial lateral concrete prestress of 0, 900, 1600, and 3200 psi (0, 6.2, 11.0, and 22.1 MPa) were used. Based on these test results and previous work, an empirical formula is proposed to predict the ultimate load of laterally prestressed slender concrete columns under eccentric load.