Pushover test and numerical analysis of zipper frames

In order to investigate the seismic performance of zipper frames, including the structural bearing capacity, lateral stiffness, failure mode and force transmission of structural members, a pushover test and numerical analysis were carried out on a 3-story and 1:2.6 scaled single-span zipper frame model. The test and numerical analysis results show that, under the lateral displacements corresponding to the frequent and design level earthquake events with intensity 8, the frame model remains in the elastic stage and no buckling is observed on the structural members. Under the lateral displacements corresponding to the rare earthquake event with intensity 8, the structural lateral stiffness is decreased obviously after buckling of the brace members. However, the structural bearing capacity doesn't decrease significantly. With the increase of lateral displacements, the unbalanced vertical force due to buckling of the brace members, is transferred upwards mainly through elongating the zipper struts. Then, the compressive force in the top story braces is increased. When the zipper frame model is unloaded, the zipper struts are subjected to compressive forces, but no buckling is found on these members. In general, the force state and force-transfer path of the structural members are basically in accordance with the design intention and the zipper frames show good seismic performance in the pushover test.