Ultimate Strength of Ribbed Slab Composite Beams with Web Openings

A series of tests is performed on composite beams with web openings. The beams have ribbed slabs with the ribs oriented transversely. The effects of slab width and moment-shear ratio on failure mode and strength are studied. Failure mode of concrete slabs depends on the slab width. Pullout failure around the shear connectors at the high-moment end occurs in the beams with wide slab width, while diagonal tension-type failure occurs in a beam with narrow slab width. Based on the test results, a strength model is developed. The maximum shear capacity is approximated as the sum of the individual shear capacity of the steel beam and the concrete slab. The shear contribution of the concrete slab is taken as the lesser of the shear strength of the slab and the pullout capacity of the studs. Strength predictions of the proposed model are compared with test results and predictions of other strength models. The proposed model is easy to use and gives satisfactory predictions.