International Concrete Abstracts Portal

In this study, a shear strengthening method for lightly reinforced concrete columns with partial height masonry infills was proposed. Perforated steel jackets are attached to one face or both faces of the column without removing the cover concrete and mortar finish. The steel jackets were designed to provide additional shear resistance to the column through the interlocking of the ribs at both ends. To investigate the seismic strengthening effects, six column specimens with partial masonry infills were tested under cyclic loading. The tests showed that the specimens with double-face jacketing exhibited an improved seismic performance, whereas there was little or no strengthening effect for the specimens with single-face jacketing. For further investigation on the short column effects due to partial height infills, modeling parameters to define the stiffness and force-deformation relation of the column and masonry walls were proposed, and the modeling results were compared with the test results. Based on the investigation results, the detailing requirements of steel jacketing and the nonlinear modeling methods of the columns with partial masonry infills were discussed.

No practically viable method exists yet to provide minimum shear reinforcements into pretensioned precast hollow-core slab (PHCS) units produced through the automated extrusion method. Subsequently, web-shear strength of PHCS units with untopped depth greater than 315 mm (12.5 in) should be reduced by half according to the current ACI 318 shear design provision. Meanwhile, continuous precast floor construction has been commonly adopted in current practices by utilizing cast-in-place (CIP) topping and/or core-filling concrete. However, shear test results on continuous composite PHCS members subjected to combined shear and negative bending moment are very limited in the literature. To this end, this study conducts shear tests of thick composite PHCS members with untopped depths greater than 315 mm (12.5 in) and various span-depth ratios, subjected to negative bending moments, where noncomposite and composite PHCS units subjected to shear combined with positive bending were also tested for comparison purposes. Test results showed that the flexure-shear strength can dominate the failure mode of continuous PHCS members rather than the web-shear failure, depending on the presence of CIP topping concrete and shear span-depth ratio. In addition, it was also confirmed that the shear strength of composite PHCS members is marginally improved by using the core-filling method under negative bending moment at continuous support, and thus its shear contribution seems not fully code-compliant and satisfactory to that estimated by using ACI 318 shear design equations.

Brittle punching failures in flat plates are precluded by ensuring adequate shear strength. Typically, this is achieved by adding shear reinforcement in the design. This paper presents an experimental and analytical study of flat plates to investigate load-resisting mechanisms associated with stirrup addition. The experimental program includes four isolated flat plates with parametric variations tested under monotonic punching loads. In terms of normalized shear strength, improvements of 22% and 29% were observed in flat plates with different layouts of stirrups, respectively, when compared with the reference specimen without stirrups. The role of longitudinal and shear reinforcements in punching resistance of flat plates was assessed through strain observations. Based on test findings, a reasonable physics-based analytical procedure for punching capacity estimation is proposed and verified using a database of 72 isolated flat plate specimens. The proposed method provided reasonably accurate capacity estimates with an overall mean test-to-estimated capacity ratio of 1.06 and a low coefficient of variation (COV) of 13%. These estimates are also compared with capacity predictions using ACI 318-19 guidelines, which resulted in an overall mean capacity ratio of 1.58 with a COV of 22%. Based on experimental and analytical results, modifications to ACI 318-19 two-way shear provisions are suggested by incorporating the key parameters in shear strength estimations, which improved the prediction accuracy to a mean of 1.25 with a COV of 13%.

Nuclear power plants use reinforced concrete shear walls with flanges for lateral load-resisting systems. The present study investigated the shear–friction strength of reinforced concrete walls with flanges by testing eight wall specimens under cyclic lateral loading. The test parameters were the flange length, flange configuration, wall thickness, interface roughness, and load direction. The test results showed that vertical reinforcing bars in the flanges, as well as the web, increased the shear–friction strength of the walls. However, due to the premature punching failure at the web–flange joint, the contribution of the thin flange was limited. Further, the shear–friction strength of the symmetric flanged wall was identical, regardless of the load direction: the shear–friction strength of the flanged wall was determined by the overall vertical reinforcing bars placed in the web and flange. The tested shear–friction strengths, including previous test results, were compared with the predictions of current design methods. Including the flange contribution in the current design methods improved the prediction of test results compared to the case that neglects the flange contribution.

Laboratory tests of deep, lightly reinforced concrete members without shear reinforcement demonstrate that the nominal shear stress at failure decreases with increasing depth and with decreasing tension longitudinal reinforcement ratio. Design procedures for one-way shear strength in ACI 318-19 incorporate these effects but result in relatively low design shear strengths for members with both large depth and low reinforcement ratio. To better understand the effects of depth and longitudinal reinforcement on shear strength, tests were conducted on beams with varying depth, a relatively low ratio of high-strength longitudinal reinforcement, and with either no shear reinforcement or minimum shear reinforcement. Loads were applied slowly and monotonically and included concentrated loads plus self-weight. Beam supports were either point supports, as in a beam, or uniformly distributed, similar to some foundation reactions. The test results demonstrate size and longitudinal reinforcement effects and suggest that a lower-bound unit shear strength may be applicable for the design of members with both large depth and low reinforcement ratio.