Experimental study on the seismic behavior of concentrically braced steel frames with extended end-plate bolted connections.

The prefabricated semi-rigid concentrically braced steel frame has always been the main form of residential steel structures, much work so far has focused on the earthquake-resistance performance of such structures. However, little attention has been devoted to systematic model testing, further effort is still required to explore the structural performance with experimental studies. Two semi-rigid concentrically braced steel frames were designed and tested to failure under reversed low-cyclic loading. The hysteretic curves, bearing capacity, energy dissipation capacity, ductility and stiffness degradation performance were studied in detail. Then the performance was compared to analyze the advantages and disadvantages of the two frames. The tests showed that the plastic deformation and damage were primarily concentrated at the braces, and the columns and semi-rigid connections exhibited hardly any plastic deformation. The specimens went through the elastic stage, elastic-plastic stage and failure stage during the tests. The results indicated the specimen with chevron braces has better seismic performance. The structure presents the characteristic of ductile failure on the whole. The steel frame and braces of the specimens cooperatively perform together so that the structure has two seismic fortification lines. The structure with chevron braces possesses an excellent bearing capacity, a high lateral stiffness, a reliable lateral-resistance performance and a strong energy dissipation capacity. In contrast, because of the premature fracture of the cross joints, the structure with X-shaped braces has a lower material utilization efficiency, which leads to a dramatic decrease in the bearing capacity and stiffness, as well as low ductility and a poor energy dissipation capacity.