IS 801 : 1975Code of Practice for Use of Cold-Formed Light Gauge Steel Structural Members in General Building Construction

IS 801:1975 is the code of practice for use of cold-formed light gauge steel structural members in general building construction. It governs structures made from thin (cold-rolled/press-braked) steel sections — purlins, girts, wall studs, floor joists, light trusses, and the Light Gauge Steel Framing (LGSF) systems now common in fast-track and modular construction. It is the light-gauge counterpart to the hot-rolled steel code IS 800.

It is read with the steel and loading stack:

• IS 800 — general construction in steel (hot-rolled; the parent design philosophy)
• IS 811 — cold-formed light gauge structural steel sections (the shapes IS 801 designs)
• IS 875 Part 1/2/3 — dead, imposed and wind loads
• IS 277 — galvanized steel sheet (the base material + corrosion protection)

Cold-formed members are *thin*, so their behaviour is dominated by local and distortional buckling of the slender plate elements long before the steel yields. IS 801's central concept is therefore the effective width (or effective section) approach: only part of a wide, thin compression element is counted as effective in resisting load; the rest is assumed buckled.

Key design themes:

• Effective section properties — computed for the actual stress, not the gross section
• Form factor / local buckling of stiffened and unstiffened elements (flanges, webs, lips)
• Lateral and torsional-flexural buckling of these open, low-torsional-stiffness shapes
• Web crippling under concentrated loads/reactions (thin webs)
• Connections — bolts, screws and welds in thin material behave differently (tilting/bearing/pull-out), and the cold-working raises yield at the corners

The section that 'looks' adequate on gross properties can be far weaker once effective widths and buckling are applied — that is the whole point of IS 801.

Brief: a lipped-channel cold-formed purlin spanning between portal frames, carrying sheeting dead load + wind.

Step 1 — loads: dead (sheeting + self) and wind suction/pressure to IS 875 Part 3; wind uplift often governs (net suction reverses the stress).

Step 2 — effective section: for the compression flange/web under the design moment, compute effective widths per IS 801 — the gross section modulus is reduced to an *effective* one.

Step 3 — moment capacity: allowable bending = f × Z_effective (working-stress basis of IS 801); check against the span moment for both gravity and uplift cases (the compression element swaps under uplift).

Step 4 — buckling/restraint: the unrestrained compression flange under uplift needs sag rods/anti-sag or the lateral-buckling capacity governs; check it.

Step 5 — web crippling at supports under the reaction.

Select the lightest IS 811 section whose *effective* capacities pass all cases — not the one that passes on gross properties.

1. Using gross section properties. The defining error — cold-formed capacity must use effective widths/section; gross properties dangerously over-state strength.

2. Designing only the gravity case. Wind uplift reverses the stress and unrestrains the other flange; many purlin/girt failures are uplift, not gravity.

3. Ignoring web crippling. Thin webs fail locally at supports/point loads — a check with no hot-rolled equivalent that is routinely missed.

4. Treating screw/bolt connections like thick-steel joints. Thin-material fasteners fail by tilting, bearing elongation and pull-out/pull-over; design to the cold-formed connection rules.

5. No anti-sag/lateral restraint. Slender open sections need sag rods/bridging; without them lateral-torsional buckling, not bending, governs.

• IS 800 — general construction in steel (hot-rolled; parent code)
• IS 811 — cold-formed light gauge structural steel sections (dimensions)
• IS 875 Part 3 — wind loads (uplift governs light roofs)
• IS 277 — galvanized steel sheet · IS 2062 — structural steel
• IS 1367 — fasteners · IS 811/IS 4923 — cold-formed/hollow sections

IS 801:1975 is old and working-stress based, while international cold-formed practice (AISI S100, Eurocode 3 Part 1-3) has moved to limit-state, the *Direct Strength Method* and explicit distortional-buckling design. With the rapid growth of LGSF / pre-engineered light-steel construction in India, many designers use proprietary software and AISI/EN methods, citing IS 801 as the locally-referenced code while documenting the actual basis — acceptable, and usually more accurate, when declared in the design basis report.

The practitioner essentials don't change with the code edition: cold-formed steel is governed by buckling and connections, not yield. Always design on effective section, always check the wind-uplift reversal with proper flange restraint, always check web crippling, and detail thin-material connections to the cold-formed rules. A BIS revision aligning with limit-state/DSM has long been anticipated; until then, treat IS 801 as the floor and supplement with AISI/EN for slender or unusual sections.