Hollow Structural Sections (HSS) play a pivotal role in modern construction due to their versatility and structural integrity. Bending these sections to create curved members is a common practice, offering architects and engineers flexibility in design. This article explores various bending techniques, essential considerations, and cost factors associated with bending HSS in steel construction.
Understanding Top 7 Bending Techniques
Bending HSS requires specialized techniques tailored to achieve precise curvatures while maintaining structural integrity. Several methods are commonly employed:
- Pyramid Rolling or Cold Bending: Utilizes a three-roll bending apparatus to create constant radius curves.
- Involves varying the distance between rolls with successive passes to achieve desired curvature.
- Gag Pressing or Point Bending: Applies a small number of point loads using a hydraulic ram to create curved members, typically used for large radii.
- Hot Bending: Involves local heating followed by bending, commonly used for repairing straightening bridge girders after structural damage.
- Rotary-Draw Bending: Clamps the HSS into a form and draws it around a die with a specific bend radius, often used for large-scale production projects.
- Induction Bending: Utilizes an electric coil to heat a short length of the HSS before drawing it through a process similar to rotary-drawing, allowing tighter bends.
- Synchronized Incremental Cold Bending:Applies loading at multiple points along the length in a synchronized manner, resulting in tight radii with minimal distortion.
Considerations in Bending HSS
Several factors influence the bending process and the achievable radii of HSS:
- Bending Method: Cold bending methods are prevalent, each with its advantages and limitations.
- Wall Support during Bending: Properly supporting side walls during bending is crucial to minimize deformations.
- HSS Shape and Wall Thickness: Round HSS is easier to bend than square/rectangular sections, and thicker walls allow for lower bend radii without distortion.
- Bending Axis: Bending around the “strong axis” versus the “weak axis” affects susceptibility to deformation.
- Steel Yield Strength: Higher strength steels are less prone to over-straining and deformation during bending.
- Permitted Distortions and Surface Quality: Standards for allowable distortions and surface conditions vary, especially for Architecturally Exposed Structural Steel (AESS).
Minimum Bending Radii and Contemporary Practices
Determining minimum bending radii for HSS involves numerous variables and considerations, such as the bending method, support, shape, wall thickness, bending axis, steel strength, and permissible distortions. Tables providing typical contemporary cold bending radii aid in understanding bending capabilities for different HSS shapes and sizes.
Cost Considerations in Bending HSS
While construction costs are often evaluated based on material weight, the cost of bending HSS is primarily determined by the time taken to bend each member. Bender/rollers generally quote project-specific costs, but a general rule of thumb suggests an estimated cost of $0.25 per pound for steel bending on smaller projects.
Conclusion
Bending Hollow Structural Sections (HSS) in steel construction demands a nuanced understanding of techniques, considerations, and cost factors. Various bending methods cater to different curvature requirements, and considerations such as wall support, shape, thickness, and steel strength significantly impact bending capabilities. Tables providing minimum bending radii aid in determining achievable curvatures, while cost factors influence project economics and budgeting. Mastering these techniques, understanding considerations, and estimating costs are essential for successful HSS bending in the realm of steel construction.
