Experimental study on cyclic behavior of thread-fixed one-side bolts bolted endplate connection to strengthened concrete filled square steel tube with fixed thread length

Abstract

This paper presented the experimental results of the Endplate Connection to Concrete Filled square Steel Tube (ECCFST) with fixed thread length via Thread-fixed One-side Bolts (TOBs) under cyclic loading. Two stiffening strategies, namely the internal polygonal tube stiffener and the cross-H section stiffener, with two stiffener flange thicknesses (18 mm and 14 mm) corresponding to two column wall thicknesses (6 mm and 10 mm), respectively, were proposed to strengthen the panel zone of the connections. Failure modes occurring for the connections were mainly affected by the weakest component of the joint region. Besides, the moment-rotation hysteretic curves and seismic performance of the joints were compared and analyzed. For all cases with fixed thread anchored length, the TOBs performed well and no thread failure occurred under the repeated reversal loading. Test results revealed that the mechanical performance of the joints can be ameliorated by adopting the strengthening components especially the cross-H section stiffener, which effectively limited the tube wall deformation from transferring the force to the opposite tube wall through the web of the stiffener. The rotation capacity and ductility of ECCFSTs were satisfactory and can meet the ductility limitation with regard to FEMA-350, demonstrating a potential for ECCFSTs in practical application.