Hollow structural steel (HSS) is becoming more and more common in structural designs. According to AISC, HSS now accounts for about 18 percent of the structural steel market. HSS has become more popular recently because of aesthetics and its superior resistance to lateral torsional buckling. In terms of curved HSS, we see it being used for AESS (architecturally exposed structural steel) and trusses.
Curved HSS – whether it is circular, square or rectangular – has its challenges. When bending HSS, there is typically some deformation of the cross section. The tighter the radius, the higher the deviation from the original dimensions. In some cases, if the radius is small enough there could be height and/or width differences up to +/- 1/2 inch depending on the size and thickness of the section. Such difference could be difficult to hide if the design includes two HSS tubes, especially if one HSS is rolled and one is not. This is called meeting face-to-face or cross section to cross section and is shown in the picture below.
In most cases, the pressure needed to create the required radii will cause different amounts of deformations in the hollow sections. For similar radii, the difference could be minimal. Increasing material thickness can help minimize deformation, as can creating a larger the radius.
If designs or material sizes cannot be altered for the curved HSS, there are different options to minimize the impact of curved steel deformation. Rolling members holding a straight tangent in one or both ends or changing the splicing points are two options. Also accommodating the rolling/bending or heat induction bending procedures to reduce joint misalignments. CMRP estimators and engineers have extensive knowledge when it comes to curving HSS and can help with any technical questions in the early design stages of the project.