Cyclic loading tests on the bottom connections of a municipal tunnel composed of composite walls and CIP bottom slabs

In order to investigate the seismic behaviors of the bottom connections of a municipal tunnel composed of composite walls and cast-in-place (CIP) bottom slabs, four full-scale specimens were tested under low reversed cyclic loading. The specimens included one exterior composite connection PCJ1, one interior composite connection PCJ2, and the corresponding CIP connections RCJ1 and RCJ2. Note that the haunch was designed in the exterior connections. The test results revealed that the failure patterns of the composite connections and CIP connections were both characterized by flexural failure at the end section of the vertical or bottom slabs. The hysteresis loops of the composite and CIP connections were similar to each other, while those of CIP connections were relatively plumper. The loading capacities of the composite connections were slightly higher than those of the CIP connections (PCJ1 was approximately 2% higher than RCJ1, and PCJ2 was approximately 17% higher than RCJ2). The ductility coefficients of the specimens ranged from 2.14 to 6.61, indicating that all the specimens behaved in a ductile manner. The stiffness degradations of the composite connections were similar to those of the CIP connections, while the energy dissipation of the composite connections was relatively lower. On this basis, the safety margins of the composite connections were evaluated. Copyright ©2021 Journal of Harbin Engineering University.