Novel beam-column joint with the folded plates for improving progressive collapse resistance of steel-frame structures

To improve the progressive collapse resistance of steel-frame structures, a novel type of reinforced joint is formed by welding the folded plates between the inner side of the I-shaped beam flange and column. Monotonic load tests were first conducted on the original and reinforced joints, and finite element models were validated by the test results. Collapse resistance of the reinforced specimen without a welding fracture was analyzed, where the effects of the folded-plate thickness, length of the straight segment connected to the column, and length of the folded segment on the collapse resistance of the novel reinforced joint were investigated. Design recommendations of the reinforced joint were also proposed. Results show that the load of the original specimen decreased after the upper-beam flange fractured near Section W2. The failure mode of the reinforced specimen was the simultaneous fracture of the upper-beam flange and folded plate near Section E2. Compared with the original specimen, the bearing capacity of the reinforced specimen increased by 21.1% due to the existence of the folded plates, indicating that the folded plates have feasibility in improving the collapse resistance. Compared with the original specimen, the ultimate bearing capacity and corresponding theta of the reinforced specimen without a welding fracture increased by 144% and 70%, respectively. The folded plates significantly improved the collapse resistance of the steel-frame structures. The sequential fracture of the beam flanges and folded plates were thus proven to provide a safe reserve for frame structures.