IS 1161 : 2014Steel Tubes for Structural Purposes - Specification

IS 1161:2014 is the specification for steel tubes for structural purposes — the circular hollow sections (CHS) used in tubular trusses, towers, columns, space frames, sheds, handrails and scaffolding. It is the material spec behind every structural tube; the *design* of tubular members is to IS 800.

It sits in the structural-steel stack:

• IS 800 — general construction in steel (design of tubular members/connections) · IS 2062 — structural steel plate/section (the comparator material)
• [IS 806] IS 806 — use of steel tubes in general building construction · IS 816 — welding · IS 808 — open-section dimensions

IS 1161 specifies light / medium / heavy tube classes, the standard outside-diameter × thickness range, the steel grade (yield strength designations) and the tolerances, ends and tests (tensile, flattening, bend, hydraulic/leak as applicable):

• A circular hollow section is highly efficient in compression and torsion (radius of gyration equal in all directions, no weak axis) — the reason tubular trusses/columns and towers use it
• The class (light/medium/heavy) sets the wall thickness for the same OD — structurally critical: a 'light' tube substituted where 'medium/heavy' was designed fails capacity and local buckling checks
• Designation by yield strength must match the IS 800 design assumption

The engineering point: tube selection is OD + wall thickness (class) + steel grade, and the recurring failure is treating tubes by diameter alone — substituting a thinner class or a lower grade than designed silently removes section capacity and buckling resistance that IS 800 assumed.

Scenario: a compression member in a tubular roof truss designed to IS 800.

Step 1 — design demand: IS 800 gives the required section (OD, wall thickness) and steel grade/yield for the axial + buckling demand.

Step 2 — specify the right tube: IS 1161 tube of the correct class (light/medium/heavy → wall thickness) and grade — not just 'X mm dia pipe'.

Step 3 — verify on delivery: check OD, wall thickness and the grade/test certificate; a thinner class than specified is a hidden capacity loss.

Step 4 — connections: weld per IS 816 (tubular joints — profile cuts, weld throat) to the IS 800 connection design.

Step 5 — corrosion: tubes are sealed-section sensitive — detail end caps/galvanising to keep the inside dry.

Get OD + class + grade right and the efficient hollow section performs as designed; substitute a light tube for a medium one and the truss is under-capacity invisibly.

1. Specifying tubes by diameter only. Class (light/medium/heavy = wall thickness) and grade are structurally decisive — diameter alone under-specifies.

2. Substituting a lighter class / lower grade. Silently removes the section capacity and buckling resistance IS 800 assumed.

3. Confusing structural tube with plumbing/GI pipe. Non-structural pipe to a different standard is not an IS 1161 structural tube.

4. Ignoring internal corrosion. Hollow sections trap moisture — seal ends / galvanise; an internally-corroded tube loses wall thickness.

5. Welded-joint detailing. Tubular connections need correct profile cuts and weld throat (IS 816) — a poor tubular joint, not the tube, is often the weak link.

• IS 800 — general construction in steel (design of tubular members) · IS 806 — use of steel tubes in building
• IS 2062 — structural steel (plate/section comparator) · IS 808 — open hot-rolled section dimensions
• IS 816 — metal-arc welding · IS 1608 Part 1 — tensile testing (acceptance)
• [IS 1239] IS 1239 — mild steel tubes (plumbing — *not* structural)

IS 1161 is current (2014) and underpins all tubular steel construction, which is structurally elegant precisely because the circular hollow section has no weak axis — superb in compression and torsion. The chronic field error is procurement-level: ordering tubes by diameter alone and accepting whatever class/grade arrives, when wall thickness (light/medium/heavy class) and steel grade are exactly what IS 800 sized the member on. A thinner class or lower grade than designed is an invisible capacity and buckling-resistance loss. Specify OD + class + grade, verify wall thickness and the test certificate on delivery, detail tubular welded joints properly (IS 816), and seal the sections against internal corrosion — then the efficient hollow section delivers the economy that makes tubular construction worthwhile.