Behavior of square fiber reinforced polymer–high-strength concrete–steel double-skin tubular columns under combined axial compression and reversed-cyclic lateral loading

• Six square FRP–HSC–steel DSTCs are tested under axial and cyclic lateral loading.
• Effects of axial load, column aspect ratio, steel tube size and concrete fill are studied.
• Square DSTCs exhibit ductile behavior under combined axial compression and cyclic lateral load.
• An increase in axial load and a decrease in aspect ratio result in a decrease in the lateral drift capacity.
• Concrete-filling the inner steel tube leads to a significant increase in the lateral drift capacity.

This paper presents an experimental study on seismic behavior of square fiber reinforced polymer (FRP)–concrete–steel columns. Six hybrid double-skin tubular columns (DSTCs) manufactured using high-strength concrete (HSC) were tested under combined axial compression and reversed-cyclic lateral loading. The main parameters under investigation were the axial load level, size of inner steel tube, provision (or absence) of a concrete-filling inside the steel tube, and the column aspect ratio. The results indicate that, in general, square DSTCs exhibit very ductile behavior under combined axial compression and reversed-cyclic lateral loading. However, the important influence of the axial load level on the column behavior is evident, with an increase in the load level leading to a significant decrease in the lateral deformation capacity of DSTCs. The results also indicate that a DSTC with a larger inner steel tube exhibits lower lateral displacement capacity than that of a companion DSTC with a smaller inner steel tube. It is shown, however, that provision of a concrete-filling inside the inner steel tube leads to a significant increase in the lateral deformation capacity of a DSTC with a larger inner steel tube to a level that is higher than that seen in a companion DSTC with a smaller hollow inner steel tube. Experimental results are presented together with accompanying discussions on the influence of the investigated parameters on the seismic behavior of square DSTCs.