International Concrete Abstracts Portal

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.

The present study investigated the contribution of slabs to the lateral load-carrying capacity of shear walls coupled with slabs. Cyclic lateral load tests were conducted on five two-story wall specimens at half scale. The test parameters included the thickness of the slab, the wall opening length, the use of punching shear reinforcement, and the use of parallel walls. The test results showed that, due to the slab effect, the strengths of the coupled wall specimens were 38 to 88% greater than the strength of walls without the slab effect. Furthermore, the initial stiffness of the specimens was significantly increased by the slab effect. During early loading, local failure of the slabs occurred at the wall-slab connection. However, the coupled walls exhibited ductile behavior up to a 2% drift ratio, without significant degradation of strength. Nonlinear finite element analysis was performed on the test specimens. Based on the results, the initial stiffness and effective stiffness of the walls and coupling slabs were evaluated for the seismic design of coupled walls.

This study presents an analytical model for estimating the effective compressive strength of a reinforced concrete (RC) column intersected by a floor slab made of relatively low-grade concrete. The proposed model is based on a theoretically sound background and considers the force equilibrium and strain compatibility conditions in the vicinity of the interface between the upper and lower columns and an intervening slab. By using the parametric study results obtained from finite element analyses, the effects of the confinement provided by the surrounding slab and the secondary stresses induced by the Poisson effect in the columns and slab panel zone were formulated in detail. A simple design expression was then derived for the better applicability of the proposed method for the estimation of the effective compressive strength of the exterior and interior columns with an intervening slab, in a unified manner. To verify the proposed model, the test results of 81 exterior columns and 24 interior columns were collected from the literature. It was found that the effective compressive strengths obtained by the proposed methods were in good agreement with these test results.

Shotcrete used for rock tunnel linings calls for skilled technicians, which is the key aspect to control the rebound. Three-dimensional (3D) concrete printing of tunnel linings has the potential to reduce manual labor for construction workers and to eliminate rebound, especially at overhead positions. In this study, the sag resistance and bond properties of printable concrete for overhead applications were explored. Mixtures with the addition of redispersible polymer powders (RDPs) and cellulose ethers (CE) were formulated. Roughened concrete slabs were used to replace the tunnel wall rock. A tack test with a loading control mode and a stress growth test were performed. To verify the results of the tack test and the stress growth test, a 3D concrete printing test, involving upside-down printing against the lower face of a supported concrete slab, was performed afterward. Also, a pulloff test was performed to measure the bond strength of the printed layers in the hardened stage. The results showed that the sag resistance of printable concrete is related to two aspects: the adhesion at the interface and the shear resistance of the fresh material itself. The adhesion and shear resistance properties determined two different failure modes: adhesion failure and cohesion failure. The results also demonstrated that the tack test results were more consistent with the upside-down printing test results, compared to the stress growth test.

Eccentric loading or compatibility conditions can cause beams in buildings to be subjected to significant torsions. Although design procedures for torsion are based on tests of stand-alone members and require closed stirrups to be used as transverse reinforcement, interior girders in beam-and-girder construction are usually integral with floor slabs and reinforced with open stirrups. This paper describes an experimental investigation of two post-tensioned companion specimens, designed to represent interior beams with an integral slab, which were loaded to failure under combined moment, shear, and torsion. The specimens were identical, except one was detailed using open stirrups and the other using closed stirrups. The strength of these members was significantly underpredicted by the ACI 318-19 and CSA A23.3-19 codes, which were, on average, conservative by factors of 3.50 and 2.05, respectively. The specimen detailed with open stirrups did not demonstrate a significantly different torsional response than the specimen containing closed stirrups.