Have you worked on a building project that included bent steel and then had to answer RFIs because you were not exactly sure what the detailer or bender needed to produce that curved member? Here are several very important but very simple items that should be included in construction drawings when dealing with curved steel.
What are you trying to bend—what is the member shape and size?
This is simple and straightforward, but the benders often see requests for an estimate without a member size, and there is a big difference between bending a W8×10 and a W40×215. Plus, don’t forget to list the grade of steel for the member, and if it must be domestically produced.
There are many ways to bend or roll everything from thin sheet metal and flat bars to large beams and tubes. However, there are many variables that can affect the quality of a bend, so we have to choose the best way to bend and roll the metal profiles to ensure the quality of the parts will meet the desired result.
So the shape and size of the bend are important.
- The shape of the bend has determined the choice of the bending process, is it cold bending or hot bending? Is it roll bending or stretch bending? etc.
- The size of the metal profile is a concrete manifestation of the processing capacity: how big a machine do you need?
How about the orientation of the member?
The table on the Bending Styles page shows several different member shapes with common terminologies:
- “Easy way” is bending a member around its weak axis
- “Hard way” is bending around the strong axis
- “Flanges in” or “Flanges out” refers to the direction of the flanges on channels, angles, and tees;
- When an angle is curved on its diagonal, is the heel (the intersection of each leg) oriented in, out, or up?
Easy way Usually ordinary workshops or equipment can easily complete these tasks.
The hard way bending in the strong axis direction is manifested as the curling of the H beam on the structural parts, which requires a hydraulic device to prevent the deformation of the abdomen.
Interestingly, when we bend U-shaped aluminum profiles, the difficulty of “Easy way” (weak axis) is greater than that of “Hard way” (strong axis), because we need to control the side deformation of aluminum materials with different properties. At this time, we will suggest customers choose T4 or T5 material.
Is the section an AESS member?
Note whether the section is going to be used in an AESS (architecturally exposed structural steel) application—tolerances will be tighter and more attention will be paid to possible imperfections or distortions. Of course, this could increase the cost of bending, so be sure it’s specified sparingly—such as when the steel is within 20′-0″ of the viewer’s eye level.
Finally, we emphasize again, please be sure to be clear about the bending direction when asking, and it is best to note the allowable deformation amount.
What about the radius?
Be sure to label the correct radius. If you have a W8×10 bent the hard way and you need the inside radius to be 10′, then label that on the drawings.
The equipment you choose will depend on the shape to be bent and any special end-use requirements.
The most practical, accepted, and economical way to make large-radii bends generally is to cold-roll the material. Many variables have a bearing on the type of equipment you should choose, including the wall, flange, and leg thickness.
For large-radii bends, cold rolling achieves the desired radius with a minimum number of passes. Because of their size, wide-flange beams can be cold-rolled as well. The larger the radii, the easier cold rolling is.
Hot bending can be applied to 1.5D bending, which is a task that cannot be accomplished in cold bending.
What is the total length required?
A final item to note is the trimming requirement. If you have a 25′ length of beam, only 22′ to 23′ of that beam may be bent due to the placement requirements within the bending machine. Note the total length of beam needed on the drawings for the estimator, material purchaser, and detailer. The last thing you want to hear from the field is that the beam is short.
Ask the experts
What if you have a spiral channel stringer for a staircase that needs to be bent in both directions? How do you go about detailing that properly? What about that thin-walled HSS tube? Can it be bent to a 16′ radius without buckling the walls?
Works Cited: Bending and Curving, Bending hot ‘n’ cold