  a hollow structural section (hss) is a type of metal profile with a hollow tubular cross section. the term is used predominantly in usa, or other countries which follow us construction or engineering terminology. hss members can be circular, square, or rectangular sections, although other shapes are available, such as elliptical. hss is only composed of structural steel per code. hss is sometimes mistakenly referenced as hollow structural steel. rectangular and square hss are also commonly called tube steel or structural tubing. circular hss are sometimes mistakenly called steel pipe though true steel pipe is actually dimensioned and classed differently from hss. (hss dimensions are based on exterior dimensions of the profile, while pipes are essentially dimensioned based on interior diameters, as needed to calculate areas for flow of liquids.) the corners of hss are heavily rounded, having a radius which is approximately twice the wall thickness. the wall thickness is uniform around the section. in the uk, or other countries which follow british construction or engineering terminology, the term hss is not used. rather, the three basic shapes are referenced as chs, shs, and rhs, being circular, square, and rectangular hollow sections. typically, these designations will also relate to metric sizes, thus the dimensions and tolerances differ slightly from hss. ==use in structures== hss, especially rectangular sections, are commonly used in welded steel frames where members experience loading in multiple directions. square and circular hss have very efficient shapes for this multiple-axis loading as they have uniform geometry along two or more cross-sectional axes, and thus uniform strength characteristics. this makes them good choices for columns. they also have excellent resistance to torsion. hss can also be used as beams, although wide flange or i-beam shapes are in many cases a more efficient structural shape for this application. however, the hss has superior resistance to lateral torsional buckling. the flat square surfaces of rectangular hss can ease construction, and they are sometimes preferred for architectural aesthetics in exposed structures, although elliptical hss are becoming more popular in exposed structures for the same aesthetic reasons. in the recent past, hss was commonly available in mild steel, such as a500 grade b. today, hss is commonly available in mild steel, a500 grade c. other steel grades available for hss are a847 (weathering steel), a1065 (large sections up to 50 inch sq made with saw process), and recently approved a1085 (higher strength, tighter tolerances than a500). ==manufacture== squ
Structural_engineering