Experimental Investigation of the Rotational Behaviour of Apex Connections in Cold-Formed Steel Portal Frames

Abstract

An experimental campaign was set up to investigate the rotational stiffness and capacity of four different types of apex connections for use in cold-formed steel portal frames. Type A connections were constructed by bolting only the channel webs to a central bracket and provided a benchmark configuration. These connections were observed to fail by cross-sectional instability immediately adjacent to the first line of bolts. Type B connections featured additional bolts in the top flanges of the rafter channels. This configuration successfully moved the location of failure away from the connection and resulted in a modest increase in the rotational stiffness of 12%. Type C connections contained an additional haunch to accommodate bottom flange bolts. A more significant increase in rotational stiffness of 44% over the Type A connections was achieved. Type D connections also contained a bottom haunch and benefitted from a direct connection between bracket and channel top and bottom flanges. The rotational stiffness exceeded that of the Type A connections by 73%. However, the connection became prone to lateral-torsional buckling of the connection bracket.