Seismic Experimental Study of the Sidewall with Waling and Crossbeam Joint Combined Permanent and Temporary

The structural system combining the permanent structure of underground buildings and the temporary retaining and protection of foundation pits is eco-friendly, efficient, and energy-saving, and has been actively promoted in recent years. In order to investigate the seismic performance of the joint of the sidewall (diaphragm wall) with waling and crossbeam (strut) in this structural system, two kinds of specimens were produced, both of which used steels to connect the waling and the crossbeam, and steel plates and threaded steel couplers to connect the waling and the sidewall, respectively, and low-cycle repeated loading experiments were conducted. The experiment results show that the damage modes of the specimen connected with steel plates and the specimen connected with couplers are similar, both of which start with yielding of longitudinal steels in the crossbeam, collapse of the concrete at the interface between the crossbeam and the waling, and eventual rupture of longitudinal steels in the crossbeam. Compared with the two specimens, the positive ultimate bearing capacity of the specimen connected with steel plates is slightly lower than that of the specimen connected with couplers, the negative ultimate bearing capacity is slightly higher than that of the latter, and both specimens satisfied the design requirements; the positive and negative displacement ductility coefficients of the specimen connected with steel plates are 1.98 times and 1.16 times that of the specimen connected with couplers, which indicate that the former has better ductility; the strength degradation of the specimen connected with steel plates is lower than that of the specimen connected with couplers, with little reinforced concrete slip, the stiffness degradation is higher than that of the latter, but the curves vary gently, with homogeneous and steadily increasing energy consumption. Combining the seismic performance of the two specimens, it is recommended the sidewall and waling be connected by steel plates. The conclusions of the study can be used as a reference for the design of similar joints.