The structural behavior of composite cold-formed steel beam-to-column joints with different connection shapes

Cold-formed steel (CFS) is becoming increasingly popular in several countries as a promising alternative to conventional steel due to its lightweight characteristics. However, there is still a lack of data on joint behavior, particularly composite connections integrated with CFS. The shape of the connection also plays a crucial role in the performance of the composite joint. To address this issue, we conducted experimental tests on six specimens with cruciform subassemblies of CFS beam-to-column joints, each featuring a different beam-to-column connection shape. These shapes included a top and bottom seat cleat angle, a back-to-back web connection forming a box column section, and a back-to-back web connection forming a box beam section. This paper presents the experimental results, including moment capacity, rotational capacity, initial rotational stiffness, ductility, the slip of a concrete slab, and modes of failure. The results indicate that the beam-to-column joint’s configuration greatly affects its strength and behavior. Compared to the specimen with an I-section shape for the beam and column, the specimen with a box column section increased the ultimate load by 33% and reduced the deflection by 75%. The specimen with a box beam section increased the ultimate load by 90% and reduced the deflection by 71%. The top and seat angles used in the connection between the beam and column displayed high ductile properties, with a rotation capacity exceeding 30 mrad, making them suitable for plastic analysis and seismic design. While cyclic load had little effect on the ultimate strength of composite joints, it significantly increased their rotation capacity. Overall, our experimental results show that the suggested composite cold-formed steel beam-to-column connection shapes are effective in terms of stiffness and ultimate moment capacity.