An experimental study was conducted to investigate the effect of using a concrete sandwich panel as an infill wall on the in-plane behaviour of steel frames. Three large-scale, single-storey and single-bay steel frame specimens with an aspect ratio of 1·0 (two infilled frames with and without separation at the frame-to-panel interface and one bare frame) were constructed and tested under in-plane cyclic lateral loading. Based on the results, it was found that the infilled frame with full connection between the infill and frame (specimen IFM) behaved quite differently to the specimen with a discrete interface connection (specimen FSI). While specimen FSI behaved almost like a bare frame in terms of lateral stiffness and strength, the interaction between the concrete sandwich panel and the steel frame in specimen IFM led to a considerable increase in the initial stiffness, lateral strength, energy dissipation and the equivalent viscous damping ratio of the system compared with the bare frame. Moreover, by separating the infill panel from the bounding frame, the results showed increased energy dissipation capability compared with the bare frame and higher drift capacity compared with specimen IFM.
