Of all the structural steel sections that are curved in a variety of ways, one of the most difficult to curve is the steel channel rolled against the strong axis.
When bending a channel the “hard way” in a three-roll bender, the section tends to distort in a number of ways. The web tends to become compressed and, in the worst case, cripples. The flanges tend to bend in toward the center of the web and lose their 90degree angle with the web. The section also tends to twist. There sometimes is a bump in the web where it meets the flange. And the tighter the radii, the more difficult bending becomes. Similarly, the thinner the channel and the wider the web and flanges, the more difficult bending becomes. However, with the proper tooling, with the right machinery, and, most importantly, with an experienced machine operator, channels can be successfully curved even to tight radii.
What I have been talking about so far is curving structural channels, channels that have an outside sharp corner 90degree edge where the flanges meet the web. But channels can also be made by forming plate on a press brake. The resulting section typically has a radiused outside corner that takes the shape given by the press brake punch and die. A benefit of a formed channel is that it can be made to dimensions not available with structural channels, i.e. different plate thickness, different web width, and different flange height. A drawback of a formed channel is that it is more difficult to curve than a structural channel.
A current application involves curving 12.75″ x 2″ x 1/4″ formed channels to a 320′ inside radius. Although the radius is large, the web is wide and the plate is thin, the formed sections are rolling well. Since these channels are being formed to become a waler cap for a seawall near a resort in St. Joseph, Michigan, appearance was a big concern. This is the first time these engineers have used formed steel channels for the cap. I think they will be happy with the product.
