# Structural Steel Tube

Structural steel tube is widely used in the building construction industry. Due to the varieties of steel tube dimensions available in the market, their usage in constructing building component is unlimited. These structural members can be used for beams and columns in steel tube buildings.

**For A36 rectangular steel tube pricing click here or here for A36 square tubing.These links will prompt to select the tube size. For rectangular tubes the letters A & B represent the two sides, and C represents the thickness. For square tubes A represent the two sides and B thickness - all dimensions are inches, conversions to millimeters are also available. Once the tube size is selected a screen with pricing will appear. Please note these tube sizes are A36 steel, when using the design formula shown below to select the tube size needed, use Fy 36 ksi in lieu of 46 ksi, everything remain the same.

The varieties of steel tube sizes available square tube, retangular tube , and circular tubes enable different applications of their usage. A square tube for example due to its symmetrical view in all direction are well suited for columns and diagonal brace members, very common at architecturally exposed structural steel braced frames. Similarly round tubes can be used the same way for the same reason as the square tubes.

Rectangular tubes on the other hand are more suited for steel beams and girders. By placing the long side of the tube vertical, assuming the load is parallel to the long side, will greatly increase its load carrying capacity.

For example, a 4x4 tube, size designation HSS4x4x1/4 section modulus of 4.11 in^3, weighs 12.21 pounds per foot. In comparison to the smallest 10 inch rectangular beam HSS10x2x3/16 weigh 14.53 pounds per foot with section modulus of 8.74 in^3. With slight increase in weight, 16%, the 10 inch tube will more than double the load carrying capacity of a 4x4 tube of the same wall thickness.

Lets take a look at the load carrying capacity in terms of pounds:

Moment formula M = wL^2/8

Section modulus (S) = M/.66Fy

Fy is yield strength of HSS is 46 ksi.

Substituting M; we have S=wL^2/8/(.66Fy) and solve for w yield w = (.66Fy)S*8/L^2.

For a 10 feet long beam HSS4x4x1/4 & HSS10x2x3/16

w = .66*46*4.11*8/120^2 = .069 kip/in = 831.9 lbs/ft or 8,319 pounds at mid span

w = .66*46*8.74*8/120^2 = .147 kip/in = 1769 lbs/ft or 17,690 pounds at mid span.

As the section modulus suggested, 10 inch deep tubular beam more than double the load capacity of a 4 inch square tube.

Refer to steel patio cover plans where structural steel tubing are being used for columns.

Per AISC (American Institute of Steel Construction) steel structural tubing needs to be ASTM A500 grade B with Fy (yield stress) of 46 ksi. Also used for structural application is A500 grade C with Fy=50 ksi

For steel tubing used for architectural purposes, ASTM A500 grade A with Fy = 39 ksi.