What Is Steel Rectangular Tubing?
Rectangular steel tubing, also called rectangular tube steel or rectangular HSS, is formed from flat steel strip into a rectangle and welded along one seam. It is used for columns, posts, frames, lintels, railings and equipment supports, because it is stiff in both directions and clean to look at.
Structural tube is made to ASTM A500 or ASTM A1085. Mechanical tubing, made to standards such as ASTM A513, looks similar but is sold for machinery and general fabrication rather than building structures, so check the specification before you price a substitute.
Steel Rectangular Tube Sizes
Rectangular tube sizes run from sections a couple of inches across, used for rails and frames, up to HSS 20 x 12 for columns and trusses. Each size comes in a range of walls, in steps such as 1/8, 3/16, 1/4, 5/16, 3/8 and 1/2 inch.
How to Work Out the Weight per Foot
For a quick weight, take the cross-sectional area of the wall and multiply by the weight of steel. A rectangular tube's area is close to 2 x t x (H + B - 2t), where H and B are the outside dimensions and t is the wall, and steel weighs about 3.4 pounds per foot for every square inch of area.
For HSS 6 x 4 x 1/4, the area is 2 x 0.25 x (6 + 4 - 0.5), which is 4.75 square inches, and 4.75 x 3.4 gives about 16.2 pounds per foot, so a 20 ft length weighs about 323 pounds. Use the published weight from the AISC Steel Construction Manual or the mill for the bid, since it comes in a little lower because the formula ignores the rounded corners. The metal tonnage calculator totals the weight across a whole list.
How to Take Off Rectangular Steel Tube
- List every tube by size and grade, from the framing plans, sections and details
- Measure each piece's length, including any coped or mitered ends
- Convert to weight with the published pounds per foot, then total by size
- Plan the cuts onto stock lengths, so the drop is counted as waste instead of disappearing, which is what nesting does
- Add what comes with the tube: cap and base plates, welds, vent holes if it is hot-dip galvanized, and the finish
Common Mistakes on Tube Steel
The one that costs the most is pricing the drawn length without the cutting drop. Tube comes in stock lengths, so a 14 ft piece cut from a 20 ft length leaves 6 ft that either finds another use or becomes scrap.
The other regulars are reading the size in the wrong order, mixing up structural HSS with mechanical tubing, forgetting cap plates and vent holes, and taking weight from the nominal size without checking the published tables.
