Erin J. Gachne Conaway, P.E., LEED AP and Jacinda L. Collins, P.E.
Every piece of structural steel experiences some form of bending during its life. Straightening, cambering, and curving of structural shapes are all representative of bending. W-shapes are straightened at the mill to a curvature that is within the tolerances as specified in ASTM Specification A6/A6M. Camber, or curvature, is often fabricated into structural steel beams to compensate for deflection. But it is the third reason for bending structural steel that is often misunderstood or just unknown.
What is "curved steel"? The use of curved steel in building projects is a growing trend that can benefit any type of project. Curved steel is used to increase visibility and provide more architectural freedom in aesthetics and functionality. But as curved steel has increased in popularity, so have the questions about it. "Who curves steel?" and "How is it curved?" are two common questions that many design professionals have.
Bending/Rolling is carried out by a "Bender", who is typically a specialty subcontractor of the fabricator. Curved steel is readily available for most projects, as there are many qualified bender-rollers located across the US. Many different bending techniques exist, and each process has its advantages and specific characteristics. The six most widely used bending processes in the industry are included in Table 1, listed in order based on prevalence of use in the industry.
Table 1: Bending process.
It is important for design professionals to recognize that different levels of quality and consistency are associated with each bending process, tooling and material size/thickness. Benders, if included early in a project, can help provide assistance on what is and isn’t feasible concerning a design, and can help save time and money as a project moves forward. In all cases, a qualified bending company is going to know what process is necessary to meet the design and quality requirements. Curved steel can provide many readily available options to benefit all project types - big or small - if properly understood and specified.
Do you have more questions about bending? Detailed questions regarding the visual appearance of a specific member with a specific bend and cost implications for a given configuration are best handled by contacting an AISC member bender-roller. For a list of AISC member bender-rollers and other bending information, visit www.aisc.org/benders.▪
Erin J. Gachne Conaway, P.E., LEED AP is the Intermountain West Regional Engineer with the American Institute of Steel Construction. Erin may be contacted at conaway@aisc.org.
Jacinda L. Collins, P.E. is an AISC Steel Solutions Center advisor. Jacinda may be contacted at collins@aisc.org.
References
The references below provide more information and guidance. Detailed questions regarding the visual appearance of a specific member with a specific bend and cost implications for a given configuration are best handled by contacting an AISC member bender-roller early in the process. For a list of AISC member bender-rollers and other bending information, visit www.aisc.org/benders or contact AISC’s Steel Solutions Center at 866.ASK.AISC or solutions@aisc.org.
ASTM International. ASTM A6/A6M—08: Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes, and Sheet Piling, 2008.
American Institute of Steel Construction. Code of Standard Practice for Steel Buildings and Bridges, 2005.
Bjorhovde, Reidar "Cold Bending of Wide-Flange Shapes for Construction". Engineering Journal, fourth quarter, 2006.
Alwood, Todd A. "What Engineers Should Know About Bending Steel." Modern Steel Construction, May 2006.
Smith, Brian and Geoff Weisenberger. "A Conversation with a Bender." Modern Steel Construction, July 2008.
Barnshaw, Russ. "Bending Considerations in Steel Construction." Modern Steel Construction, October 2009.