Experimental investigation of long-span cold-formed steel double channel portal frames

Abstract

Cold-formed steel haunched portal frames are popular structures in industrial and housing applications. They are mostly used as sheds, garages, and shelters, and are common in rural areas. Cold-formed steel portal frames with spans of up to 30 m (100 ft) are now being constructed in Australia. As these large structures are fairly new to the market, there is limited data on their behavior and design recommendations. An experimental program was carried out on a series of portal frame systems composed of back-to-back lipped channels for the columns, rafters, and knee braces. The system consisted of three frames connected in parallel with purlins to simulate a free standing structure, with a span of 14 m (46 ft), column height of 5.3 m (17 ft), and apex height of 7 m (23 ft). Several configurations were tested including variations in the knee connection, sleeve stiffeners in the columns and rafters, and loading of either gravity only or combined horizontal and gravity loads. Deflections were recorded at various locations to measure global and local movements of the structural members. A total of eight frames with unbraced columns were tested and one frame with braced columns. Experimental results are presented herein including frame strengths and failure modes for the various frame configurations and loading conditions, as well as quantified moment-rotation relations for the column base connection. The contributions and effects of the different knee connections and sleeve stiffeners are presented. The overall frame behavior of these structures and suggested design considerations are discussed.