Performance of Edge-Loaded Cold-Formed Steel Built-Up Box Beams

The flexural performance of box beams under eccentric edge loading is discussed in this paper. Physical tests show that the combined effects of edge loading and the connection of the two primary box beam components (toe-to-toe joists), by top and bottom track members, may reduce the overall strength of the box beam. In the test results reported here, the mode of failure was predominantly beam instability due to twisting. In some cases, this instability was accompanied by elastic local buckling. Ignoring any composite action between the connected components of the box beam, the combined flexural strength of the primary beam components (joist members) was computed and compared with the measured capacity. This comparison showed that, based on the measured yield strengths, edge loading has a tendency to reduce beam capacity. These limited test results suggest that additional work should be undertaken to evaluate similar edge loading conditions that are commonly found in cold-formed steel framed structures.