Tensile performance of cast-in headed studs in thin concrete panels with void formers

Abstract

In recent times, voided concrete slab or wall system has been increasingly popular due to material and cost savings benefits offered by such system. Fastenings are required to be attached to such systems either to connect to other concrete elements or fixtures. There has been limited published literature on the performance of fastenings in thin concrete shell elements due to presence of voids. The Concrete Capacity (CC) method is the state-of the-art prediction model for capacity of anchors in concrete widely adopted in design standards worldwide. The CC-method has been proven to be a robust model for predicting concrete cone capacity of cast-in and post-installed anchors with effective embedment depths, hef between 4 and 20 times diameter of anchors with a minimum hef of 40 mm in mature age concrete. In this study, over 200 headed studs are investigated experimentally in early age concrete whereby the hef for over half of the specimens is lesser than 40 mm. Further, the failure mode for the headed studs in the presence of plastic void former is expected to be a plug failure which prohibits the development of the full concrete cone. The purpose of this study is to examine the applicability of the CC-method for pull out performance of headed studs in the presence of void formers. A total of 228 headed anchors with varying effective embedment depths ranging from 19 mm to 61 mm were tested in thin concrete panels with varying thicknesses. Based on structural reliability analysis, a modification factor was proposed to the CC-method to safely predict the pull-out design capacity of headed studs in thin concrete panels with plastic void formers to maintain the same degree of safety as for typical headed stud applications within the scope of the CC-method.