International Concrete Abstracts Portal

In this study, the behavior of diaphragm-to-wall connections with collector reinforcement and construction joints was investigated. Four slab-to-wall connection specimens were tested under cyclic loading. Diaphragm connection details, such as shear friction reinforcement (i.e., slab dowel bars anchored by 90-degree hooks within the wall) and the use of spandrel beams as collectors, were considered as test variables. When fabricating the specimens, concrete was consecutively cast for the wall and slab, and construction joints were placed on the sides of the wall and spandrel beams. The tests showed that the diaphragm connections exhibited the typical ductile behavior characterized by the robust initial stiffness and subsequent post-yield plastic behavior. Before concrete failure on the front of the wall, the load transfer from the diaphragm to the wall was governed by a nodal zone action; then, the subsequent connection behavior was dominated by shear friction as sliding failure occurred on the side of the wall along the slab construction joints. The diaphragm-to-wall connection strengths were evaluated using the strut-and-tie model and shear friction theory. The calculated strengths were in good agreement with the test strengths. Based on the investigation results, design considerations of the diaphragm-to-wall connection were proposed.

Several studies have revealed that slabs with cast-in-place over precast, prestressed panels (CIP-PCP) behave differently from traditional concrete slabs because of the panel joints between the PCP components. While high-strength reinforcing bars can improve load capacity or reduce reinforcing bar quantity in traditional slabs, limited research has focused on their application in CIP-PCP slabs. This study addressed this gap by conducting four-point bending tests on CIP-PCP slabs with normal- and high-strength reinforcing bars. Two configurations of high-strength steel were used: one with the same reinforcing bar layout as normal-strength reinforcing bars and another with increased reinforcing bar spacing to reduce the reinforcing bar quantity. Additionally, slab specimens were designed to replicate real-world bridge deck conditions, including longitudinal and transverse joints, for detailed analysis. The results indicated that reducing reinforcing bar quantity by adjusting reinforcing bar spacing based on the specified yield strength ratio between normal- and high-strength steels maintained a comparable load capacity, with crack widths magnitude similar to those in normal-strength steel layout in the service state.

Although the issue of progressive collapse has been significantly studied within the broader field of structural engineering, the literature on the analysis and design of connections in precast concrete cross-wall buildings is rather limited. This study aims to investigate the progressive collapse behaviour of a typical precast floor-to-floor system, considering the pull-out failure mode of the deformed bar into grouted keyways of slabs at the joints. To do so, the pull-out behaviour of deformed bars in grouted keyways of the connections was first experimentally studied. Subsequently, by integrating the pull-out force-displacement data with findings from full-scale floor-to-floor experiments, an approximate analytical approach was formulated and validated to estimate the resistance to progressive collapse. The findings reveal that the floor-to-floor system, when subjected to the pull-out failure mode following the removal of a wall support, demonstrates a secondary peak strength and considerable ductility in contrast to the bar fracture failure mode.

No practically viable method yet exists to provide minimum shear reinforcements into pretensioned precast hollow-core slab (PHCS) units produced through an automated extrusion method. Subsequently, the web-shear strength of PHCS units with untapped depths greater than 315 mm (12.5 in.) should be reduced in half, according to current ACI 318 shear design provisions. Meanwhile, continuous precast floor construction has been commonly adopted in current practices by using 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 literature. To this end, this study conducts shear tests of thick composite PHCS members with untapped 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 show that 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 a 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 using ACI 318 shear design equations.

Due to lateral load considerations, reinforced concrete flat plates—where the slab is directly supported on columns—are usually combined with other structural elements, such as shear walls. In such structures, the slab-column connections are typically designed to resist gravity loads only and the shear walls are designed to resist both gravity and lateral loads. Therefore, the shear walls and the slab-wall connections (SWCs) are part of both the gravity and lateral force-resisting systems. While past research has demonstrated that punching shear failures of SWCs can occur, the related research is limited; therefore, design codes typically do not include specific punching shear provisions for SWCs. In this paper, a punching shear design method for interior SWCs subjected to gravity load only, developed from finite element analysis results, is presented. The presented design method is an extension of those developed for interior rectangular slab-column connections.