Why use straight structural steel frames for construction when curved structural steel can be used instead? Obviously, this is said in jest. However, in applications where a certain amount of curved structural steel is required, there are some things to understand. Firstly, not all curved structural steel is the same, or at least not curved in the same way. While different bending rollers may use similar equipment, the key lies in how they utilize that equipment, making them distinct from each other.
The Art and Methods of Bending
“Rolling and bending are largely an art rather than a science—it’s about how a company uses a certain method with a certain machine,” says Barry Feldman, president of bending roller company Kottler Metal Products. Regardless of how good the machine is, a skilled operator is needed to achieve high-quality bends. In many projects, especially in architectural applications, there may be 100 pieces, each with different radii and degrees of curvature.
Various Bending Methods
Secondly, there are various methods for bending steel. Two common types are rotary-draw/compression bending and roll bending or pyramid bending. The latter is named for the machine having three adjustable rolls in a triangle or pyramid configuration. Tighter roll spacing results in a smaller radius. The operator places the beam in the rolling machine, adjusts the three rolls’ spacing, and slowly begins rolling, frequently checking for distortion in the early passes. Additional passes are carried out, with the operator measuring the overall radius after each pass to monitor progress.
Heat Induction Method
Rotary-draw/compression bending is a different method, mainly used for complex bends in the machine and parts industry. In this process, the structural member is bent by rotating it around a die. While both methods bend steel in cold conditions, another method—heat induction—requires heating the steel during the bending process. Heat induction bending relaxes the steel, aiding in achieving tight radii and minimizing distortions.
Other Bending Methods
Two additional methods—incremental bending and rotoform bending—can also be used to curve steel. Incremental bending involves supporting steel at two ends and applying pressure at a third point, particularly useful for curving steel to high radii. The second method uses a specialized process to extrude steel from a straight condition into a bend, offering flexibility in radius parameters.
Bending Inquiries
Given the various bending methods and the infinite possibilities achievable, designers are always seeking insights. The AISC’s Steel Solutions Center has received questions about bending steel, and while AISC can provide some general guidance, it’s usually best to contact a bending roller for their expertise.
- Minimum Rolled Radius for Wide-Flange Steel: There are no strict guidelines for the minimum bending radius, as it depends on several variables. These limitations should be discussed with the bending roller providing the service. Some general guidelines can be found on page 2-37 of the AISC 14th Edition Steel Construction Manual, and the AISC website provides information related to curved members.
- Tolerances on Curved Beams: The 2010 AISC Code of Standard Practice has limited tolerances for curved members. These depend on factors such as whether the member is architecturally exposed structural steel (AESS). Discussing required tolerances with the bending roller is recommended, and adding them to contract documents ensures alignment with expectations.
- Maximum Geometric Camber for a W27 Rolled Beam: Capacities of bending rollers and fabricators vary. It’s best to consult with a bending roller and a fabricator to get their opinions.
- Possibility of a 90° Bend in a Pipe: Yes, it’s possible. The key factors are the radius and bending method. Contacting a bending roller or fabricator to discuss limits, options, and costs is advised.
Conclusion
What is the best way to bend steel? The determination of the best technique depends on factors such as the overall member size, web and flange thickness, radius requirement, and the end application of the material. Consulting with a bending roller about the best options for a particular application and their capabilities is crucial. Involving bending rollers early in a project can help assess the feasibility of a design and save time and money as the project progresses. Bending rollers are accustomed to working under pressure and can bend whatever is required in fast time frames.
Works Cited: https://www.aisc.org/
