Composite Performance of Prestressed Hollow-Core Slabs with Cast-in-Place Topping Concrete

Prestressed hollow-core slabs (PHCS) are generally fabricated through an automated extrusion method by using an extremely dry concrete mixture to maximize productivity in precast factories. In consequence, it is very challenging not only to provide shear connectors along the interface between the PHCS unit and cast-in-place (CIP) topping concrete but also to secure code-compliant intentional roughness due to its extremely hard and flat surface condition. Thus, it is difficult to have sufficient horizontal shear strength required to achieve flexural performances of the prestressed composite members. To this end, extensive pushoff tests were conducted in this study considering various interface roughness conditions, from which some viable options were chosen. Then, flexural tests on full-scale composite PHCS specimens were performed with selected surface conditions from the pushoff tests. On this basis, the applicability of various surface roughness conditions that are inevitably faced in practices is examined based on ACI 318 design criteria and nonlinear analysis. It was confirmed that sufficient horizontal shear strength can be achieved not only by properly roughened surface conditions but also by placing wire meshes between PHCS units even with no intentional roughness.