Seismic performance of composite coupling beams with diagonal steel tubes

Reinforced-concrete (RC) coupled shear walls are an efficient earthquake-resistant system governed by the performance, especially ductility, of coupling beams connecting two or more RC walls. To enhance the performance of RC coupled walls, the coupling beams need very complicated details such as diagonal reinforcements. This paper provides the experimental results for rectangular steel tube reinforced composite coupling beams, which were tested to investigate the feasibility of introducing rectangular steel tubes as an alternative to diagonal bar groups confined by transverse reinforcement to improve constructability and save construction time. Three coupling beams with a span–depth ratio of 2·0 and specified compressive strength of 80 MPa were tested under cyclic loading. Test results showed that 80 MPa concrete and a non-shrink mortar-filled steel tube composite coupling beam exhibited stable behaviour up to a chord rotation of 3·5%. The non-shrink mortar-filled steel tubes replacing diagonal bar bundles improved the initial stiffness and energy dissipation capacity of composite coupling beams compared to the empty steel tubes. It is concluded that non-shrink mortar-filled steel tubes are a feasible option to replace diagonal bar groups confined by closely spaced hoops.