Seismic behavior and initial rotational stiffness of beam-to-column composite connection in steel frame

To examine the influence of a composite slab on the seismic performance of beam–column joints of a steel frame, four specimens were tested under cyclic loading in this study. Bolted-welded connection and extended end-plate connection were used as connection forms to design and manufacture two pure steel joints (BW and BE) and two composite joints (BWS and BES). The key indices of seismic performance, including the failure mode, hysteretic behavior, capacity for energy dissipation, stiffness degradation, moment–rotation relationship, initial rotational stiffness, and strain distribution, were compared between the pure steel joints and the composite joints. According to the results of the test, a refined numerical model was established to study the mechanical law of the connection between the extended end-plate and the composite slab by using the parameters of the end-plate. The results show that the failure mode of the beam–column joints was mainly determined by the connection form, and the difference between the composite and pure steel joints was in the local crushing of the composite slabs. The composite slab and upper flange of the steel beam worked together to reduce the strain on the upper flange. Based on past work, this study also provides a model to calculate the initial rotational stiffness of the connection between the extended end-plate and the composite slab. A comparison of the results of the tests and finite element analysis showed that the proposed model for initial rotational stiffness is accurate, and offers promise for use in engineering.