Flexural behavior of ribbed composite slabs with hybrid connections

This paper proposes a hybrid connection detail for ribbed composite slabs to resolve the discontinuity in load transfer caused by interrupted longitudinal ribs at the joints of precast bottom slabs. An experimental program was conducted on four full-scale specimens, with variables including the presence of joints, the number of joints, and the steel box configuration. Three-point bending tests were carried out to examine crack development, failure modes, deflection responses, strain distributions, and slip behavior. A refined finite element model was then developed for parametric studies to evaluate the effects of steel box thickness, the number of tensile rebars in longitudinal ribs, and the number of longitudinal ribs on flexural performance. A two-stage flexural stiffness calculation method tailored to this member type is also proposed. The results demonstrate that the hybrid connection does not alter the flexural failure mechanism. The welds at the joints constitute the primary load-transfer path, whereas the bolts serve mainly for positioning and pre-tensioning, and the bottom cover plate is structurally redundant. The presence of joints reduces the post-cracking stiffness by approximately 30%–35%, yet improves the ductility coefficient. Increasing the number of tensile rebars within the longitudinal ribs from 1 to 4 enhances the ultimate load capacity by 191%, and increasing the number of longitudinal ribs from 2 to 3 improves it by 34.1%. The proposed stiffness calculation method gives deviations within 10% of the test results, thereby providing a practical reference for engineering design.