Cyclic performance of concrete-filled double-skin steel tube frames strengthened with beam-only-connected composite steel plate shear walls

The concrete-filled double-skin steel tube (CFDST) frame has been recommended as a lateral-resisting structural system; however, few investigations have been reported for seismic strengthening of CFDST frames. The aim of this paper is to investigate the cyclic performance of a CFDST frame strengthened with beam-only-connected composite steel plate shear wall (BF-BCW). The BCW is connected to the beam only by bolted connections. A BCW consists of a beam-only-connected steel plate shear wall (BSW) and a beam-only-connected RC shear wall (BRW) attached at one side of the BSW. Both experimental and theoretical methodologies are used. Firstly, three 1:2-scaled specimens were tested to analyze the failure mechanism and cyclic performance of the proposed system. Contribution of the BCW in strengthening the seismic performance of CFDST frames is quantified and compared to the contribution of the BSW. Results show that the BCW effectively enhanced the lateral stiffness and lateral strength of a CFDST frame, and it worked well due to the proposed bolt-connected frame-to-wall connections. BF-BCW specimens exhibited higher ultimate resistance by comparing with the BF-BSW specimens, indicating that composite action between the BRW and BSW in the BCW is efficient. A theoretical model is then proposed for calculating the ultimate resistance of the BCW in the test specimens; theoretical results are verified by the test results. Findings indicate that the BCW, as well as the BCW-to-frame connection, could be effectively used to strengthen existing and new CFDST frames.