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This study aimed to investigate the seismic behavior of simply supported steel–concrete composite I beam and box beam through a quasi-static experimental study. A total of 22 composite beams included in the experiments, and parameters including shear connection degree, transverse reinforcement ratio, longitudinal reinforcement ratio, section type, diameter of stud, and web thickness were investigated. Based on the test, hysteretic response, skeleton curves, failure mode, stiffness degradation, ductility, and energy dissipation were discussed. Results show the following: (1) Composite beams have favorable seismic performance, the displacement ductility ratio ranged from 2.5 to 8.75, whereas the maximum equivalent viscous damping ratio ranged from 0.219 to 0.470. (2) The higher the degree of shear connection, longitudinal reinforcement, and transverse reinforcement, the plumper the hysteretic curve and the greater the bearing and energy dissipation capacity. The ductility of composite beam increased as the longitudinal reinforcement ratio increased. The stiffness degradation and residual deformation were less effected by other parameters. (3) Findings suggest that the transverse reinforcement ratio ranged from 0.4% to 0.8%, the positive shear connection degree should be greater than 1, and the spacing of stud in the negative moment region should not be larger than that in the positive moment region. To ensure welding quality and convenient construction, a large diameter of stud should be applied in practical engineering. Moreover, when the girder is welded by a thin web, transverse diaphragm plate and vertical reinforced rib should be added in the steel girder if these areas are heavily loaded.

An experimental study of 22 concrete-filled round-ended steel tubular (CFRT) stub columns under axial compression is conducted compared with 4 circular concrete-filled steel tubular (CFT) stub columns. The influences of width–thickness ratio, concrete strength, steel yield strength and wall-thickness of steel tube on the ultimate bearing capacity of the CFRT columns are discussed. The 3D finite element (FE) model is also developed to analyze the behavior of the CFRT columns under axial compression. From the results, local buckling of the round-ended steel tube associated with shear failure of in-filled concrete could be observed. With the increasing width–thickness ratio, the corresponding load–strain curves have a shorter elastic–plastic stage. The parametric studies indicate that the concrete strength, tube thickness and width–thickness ratio of the steel tube also have a great effect on the ultimate bearing capacity. The numerical results also show that the confinement effect of the stub columns decreases with the increasing width–thickness ratio. A practical calculation formula for the bearing capacity of the CFRT stub columns is proposed, which is well in agreement with the experimental results.