Column face bending in anchored blind-bolted connections to concrete filled hollow sections

This research investigates the bending behaviour of the column face component of concrete filled tubular columns connected to other structural members via Extended HolloBolt (EHB). The effect of bolt gauge and pitch distances and anchored length were investigated by experimental tests and finite element analysis. Totally, eighteen specimens were tested and 31 finite element models were analysed. Results showed that, the concrete acts compositely with the anchored bolts until it fails by forming a cone shape starting from the anchored nut and extending to the concrete surface. The cone radius at the concrete surface is equal to 0.82 times the anchorage length. The contribution of the anchored bolts in the component plastic strength can be quantified by considering the work required to initiate concrete cracking across the cone projection on the column face. The component initial stiffness seems to be influenced significantly by the bolt gauge and anchorage length. The use of small bolt pitch or bolt gauge limits the advantage of anchoring the EHB in the concrete and the large bolt gauges result in minor yield in the column walls (g ≥ 85 % of the column face width). A Major enhancement in the component strength can be achieved by increasing the bolt anchorage length to more than six times the internal bolt diameter (d_b).