Moment capacity and fire protection of the welded plate joint for precast members

Specimens of reinforced concrete (RC) cantilever beams connected by a welded plate joint to an RC main beam were investigated. Load tests and fire tests were conducted to examine structural behavior and fire resistance of the joint. Under flexural load, the main failure modes of the joint were splitting of the welded plate and rebar yielding. The joint moment capacity depended on ability of the joint to resist tensile forces in the beam rebars. The ultimate loads were about 50% and 70% of corresponding cast-in-place specimens, for the joints with 4-mm and 6-mm thick plates, respectively. To simply estimate the moment capacity, the plate in its width direction was modeled as a beam with fixed ends, and the forces in tensile rebars acted as point loads. The proposed computation of the moment capacity was validated with the tests and with FE simulations, for both moment magnitudes and failure types. By using fire tests, fire protections of the joint such as thin or thick mortar plaster, or a flexible sealant, were investigated. The thick plaster and the sealant provided fire resistances exceeding 2 h. However, the flexible sealant coped better of these two with the separating and swelling behaviors.