Finite element modeling and parametric study of cold-formed steel portal frames

Abstract eng:
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. Coldformed 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 feasibility and design recommendations. An experimental program was carried out on a series of portal frame systems composed of back-to-back channels for the columns, rafters, and knees. The system consisted of three frames connected in parallel with purlins to simulate a free standing structure, with a span of 14 m and apex height of 6.8 m. Deflections were recorded at various locations to measure global and local movement of the structural members. Several configurations were tested including variations in the knee connection and loading of either vertical or combined horizontal and vertical loads. Finite element models of the tested frames were completed. They were calibrated with material properties from coupon tests and column base stiffness data obtained from component tests. The models were validated with the experimental results, thus confirming the suitability of the developed modeling technique to accurately capture frame ultimate capacity and deflections. Additionally, parametric studies were completed through FEM to determine the effect of various knee connections, as well as the effect of column base stiffness on frame capacity and behavior for various loading conditions. Design recommendations based on the work herein are presented. 1  Background Cold-formed steel haunched portal frames are prevalent structures in housing and industrial uses, especially in rural areas in Australia. There is a demand for the construction of larger spans, however there is a lack of test data on their performance. Previous experimental studies have been conducted on medium span double channel portal frames (Lim & Nethercot 2002, Stratan et al. 2006, Zhang 2014, Wrzesien et al. 2012) consisting of either a single frame or bay. The experimental work discussed herein aims to expand the data available to larger spans and multiple bays. An experimental program was carried out on a series of haunched portal frame systems composed of back-to-back channels for the columns, rafters, and knee braces. Members were connected together with back-to-back L brackets bolted through the webs. The experimental setup consisted of three frames connected in parallel with purlins to simulate a free standing structure, however load was applied only to the center frame. Load was applied through a hydraulic jack, which connected to a load spreading system to distribute the load from the jack to eight

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