Seismic response investigation on CFDST column to steel beam blind-bolted connections

Abstract The blind bolting technique, recognized as a novel solution to connect a beam to a closed section column for unavailable installation from one side, has been gradually employed in concrete filled steel tube (CFST) column to steel beam connections recently. However, unexpected failure modes including bulge of the thin-walled steel tube and anchorage failure of the blind bolt in the core concrete still existed for this type of connection, which resulted in a limited ductility and inferior strength of the connection. Therefore, a novel blind bolted joint was proposed by replacing the CFST column with the concrete-filled double skin steel tubular (CFDST) column to overcome the above problems. A series of interior joint specimens to square CFDST columns were carried out to investigate their seismic behavior. Compared with the CFST column joints, typical failure modes of the CFDST column joints were characterized. Seismic response was also analyzed in terms of the hysteretic performance, strength and stiffness degradation and energy dissipation capacity to explore the effects of the column hollow ratio and end plate type. The experimental results denoted the CFDST column to steel beam joint with blind bolts performed excellent seismic performance. Based on the equivalent method, two simplified analytical models were discussed to evaluate the initial stiffness of this type of joint. The experimental and analytical results were beneficial for the application of semi-rigid connections to CFDST columns in engineering practice.