Bolted shear connectors vs. headed studs behaviour in push-out tests

Prefabrication of concrete slabs reduces construction time for composite steel-concrete buildings and bridges. Different alternatives for shear connectors (bolts and headed studs) are analysed here to gain better insight in failure modes of shear connector in order to improve competiveness of prefabricated composite structures. Casting of high strength bolted shear connectors in prefabricated concrete slabs offers the higher level of prefabrication comparing to a standard method of grouting welded headed studs in envisaged pockets of concrete slabs. In addition, bolted shear connectors can easily be dismantled together with the concrete slab thus allowing the improved sustainability of the construction, simpler maintenance, and development of modular structural systems. Bolted shear connectors have been rarely used in construction, actually just for rehabilitation works, because there is a lack of design recommendation. The first step towards the design recommendation is to understand the difference between the headed shear studs and the bolted shear connectors in a push-out test. Push-out tests, according to EN1994-1-1, using 4 M16 - grade 8.8 bolts with embedded nut in the same layout and test set-up as for previously investigated headed studs were performed. Finite element models for both shear connectors were created, and good match with experimental data was obtained. Basic shear connector properties such as: shear resistance, stiffness, ductility and failure modes have been compared and discussed in detail by using experimental and FE results. Parametric FE analyses of shear connector's height are carried out and shear resistance reduction factor has been proposed for bolted shear connectors