Study on the Mechanical Behavior of Composite Special-Shaped Columns under Compression-Bending Without End Rotation Constraints

In this study, three double-plate connected L-shaped concrete-filled steel tube composite (LCFST-D) columns were subjected to axial and eccentric loading tests using spherical-hinge supports to relieve the bidirectional rotation constraints. By analyzing the failure phenomenon of the LCFST-D specimen, the rotation of the endplate, and the comparison of similarities and differences between the support of the knife-edge and the support of the spherical-hinge, the bidirectional eccentric loading performance of the LCFST-D column when the bidirectional rotation constraint was released was studied. The test results show that when the spherical-hinge support was loaded, the out-of-the-plane deflection was more evident than the knife hinge. The bearing capacity of the LCFST-D specimen decreases as the eccentricity increased. When the end rotation constraints were relieved, the failure mode of the axial and eccentric loading was nontorsional bidirectional instability. In addition, the loading tests using spherical-hinge supports were verified to effectively release end rotation constraints. A finite element model for the LCFST-D column was established, and its accuracy was confirmed. From the failure mode, deflection, bearing capacity, and rotation of the endplate, the differences between spherical-hinge, knife-edge hinge, and rigid pad loading supports and their influence on bidirectional eccentric loading tests performed on special-shaped columns were investigated. The results show that the bidirectional eccentric loading performance of the LCFST-D column can be reflected by spherical-hinge supports. The theoretical formula was used simultaneously to verify the data from the finite element model and the test.