Pull-out forces in shear connectors in composite beams with large web openings

Composite beams with large web openings are often used, and their design is controlled by Vierendeel bending at the four corners of each opening, which is assisted by local composite action with the floor slab. Development of this Vierendeel bending resistance may be limited by pull-out failure of the shear connectors. In this paper, a non-linear elasto-plastic finite element model of a composite beam with web openings was used to investigate this mode of pull-out failure. A test was performed on a typical composite slab in which the shear connectors were subject to pure tension and the failure load was 67kN, which is approximately 70% of the longitudinal shear resistance. The results of the finite element model are compared against those obtained using the established design theory, that does not limit the vertical pull-out resistance of the shear connectors. It is shown that the local bending resistance due to composite action should be reduced when limited by pull-out of the shear connectors. A parametric study investigated the effect of openings of 600 to 1200mm length. A simple model is developed to establish the Vierendeel bending resistance, when limited by pull-out of the shear connectors. •The shear force in the slab at a large web opening is based on a rigid-plastic model.•Pull-out tests were performed on a composite slab with a 60mm deep deck.•The pull-out resistance was 67kN and the longitudinal shear resistance was 96kN.•Elasto-plastic analysis of composite beams with rectangular web openings is presented.•Vierendeel resistance due to composite action is dependent on the opening length.