Bending and Curving
Structural Steel can be curved to enhance the beauty and functionality of buildings
Curved steel framing brings grace and function together in almost limitless ways. It offers new design solutions and opportunities, allowing architects to stretch their imagination and create iconic, inspirational structures that draw the eye.
Bending/rolling steel is the process of curving a steel member to a specified radius and arc length. Bending is commonly used to describe the process for a tighter radius bend, whereas rolling is used to describe a larger radius bend. (For more on the bending process, see the Modern Steel Construction article There's More than One Way to Bend a Beam.)
Bent and rolled beams, channels, angles, tees, pipe and HSS can be used as elements of roof trusses, domes, stadiums, arenas, canopies or any other structure that requires a curved aesthetic.
The bending process offers a consistently smooth finish with a consistent radius over the entire arc length. For example, if you miter-cut several pieces of steel and weld them all together to create an "arch," it would be much more time-consuming and expensive than bending—and it wouldn't look as good.
Keep in mind that bending is a separate process from generalized fabrication and takes place at a separate bender-roller facility. While some fabricators possess the know-how and equipment to bend steel, bender-rollers are typically specialty subcontractors to fabricators. Benders receive steel from the fabricator (or sometimes supply it themselves), perform the job-specific bending-rolling and then ship the curved steel back to the fabricator.
While working with curved steel adds another element to the design process, it doesn't have to complicate it . To ensure thing go seamlessly, here are several very important but very simple items that should be included on construction drawings when designing and specifying curved elements:
- Shape and size of the member to be bent. This might seem obvious, but benders often receive requests for estimates that don't include member size, and there is a big difference between bending a W8×10 and bending a W40×215. And don't forget to list the steel grade for the member as well as whether it muse be domestically produced.
- Orientation of the member. In other words, how/on what axis is the member to be bend? The table at right shows the various dimensions for curving steel. A few notes:
- "Easy way" is bending a member around its weak axis, and "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, the heel (the intersection of each leg) can be oriented in, out or up
- Note whether the section is going to be used as AESS (architecturally exposed structural steel); tolerances will be tighter and more attention will be paid to the final look of the section
- 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 ft, then indicate that on the drawings!
- A final item to consider is the trimming requirement. If the beam is 25 ft in length, only 22 ft to 23 ft of that beam may be bent due to the placement requirements within the bending machine. Be sure to note the total beam length needed on drawings for the estimator, material purchaser and detailer.
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