Experimental evaluation and component model for single anchored blind-bolted concrete filled tube connections under direct tension

This paper presents an experimental programme of single anchored blind-bolted concrete filled square steel tube connections under tension to understand the joint behaviour, with emphasis on combined failure mode. A total of eight full-scale specimens were fabricated and tested. Parameters including infill concrete, length and diameter of anchored blind-bolt, tube wall thickness and concrete strength were considered. The experimental programme is accompanied by bolt preload tests and a range of material tests for all the elements in the connection. Primarily, three failure modes of the connection were identified, viz., tube wall deformation, bolt fracture and combined failure. It was observed that, apart from the beneficial effect of bolt anchorage length in enhancing the connection performance, the combined failure mode may be preferred over other failure modes for higher ductility and collapse prevention. Concrete strength is identified as the primary influential factor determining the failure modes. A component model based on spring theory is developed for prediction of global force-deformation behaviour of the bolted connection. Based on this analytical model, the strength and stiffness of such a complex connection can be predicted with good accuracy.