IS 800:2007 — “General Construction in Steel: Code of Practice” — moved Indian steel design from the old working stress method to the limit state method, aligning it with international practice.
Steel is increasingly common in Indian residential and light-commercial work: mezzanines, stair stringers, canopies, roof trusses over halls, and full pre-engineered structures. Here are the essentials of how IS 800 thinks.
Limit state method and partial safety factors
Like IS 456 for concrete, IS 800:2007 checks ultimate (strength) and serviceability (deflection, vibration) limit states with partial safety factors on loads and resistance.
| Resistance governed by | Symbol | Value |
|---|---|---|
| Yielding | γm0 | 1.10 |
| Ultimate stress / rupture | γm1 | 1.25 |
| Bolts — friction & bearing type | γmb | 1.25 |
| Welds — shop / field | γmw | 1.25 / 1.50 |
Section classification: will it yield or buckle first?
Before any strength check, IS 800 classifies the cross-section by how slender its plate elements are — because a thin flange can buckle locally before the steel ever reaches yield.
- Plastic (Class 1): can form and rotate a plastic hinge — needed for plastic analysis.
- Compact (Class 2): can reach the full plastic moment, limited rotation.
- Semi-compact (Class 3): can only reach the yield (elastic) moment.
- Slender (Class 4): local buckling governs; effective-section methods required.
Members: tension, compression, and beams
- Tension members: check gross-section yielding (Ag·fy/γm0), net-section rupture at bolt holes (0.9·An·fu/γm1), and block shear. Rupture at holes surprises many first-time designers.
- Compression members: strength depends on the slenderness ratio (KL/r) through four buckling curves a–d, which account for imperfections. Column strength drops steeply with slenderness — doubling the unsupported length can more than halve the capacity.
- Beams: a laterally unrestrained beam fails by lateral-torsional buckling below its section capacity. Restraining the compression flange (e.g., by a slab or purlins) is the cheapest strength upgrade in steel design.
- Deflection limits (serviceability): typically span/300 for beams under live load, span/150 for cantilevers (Table 6 gives the full set).
Connections: where steel structures actually fail
Most steel failures trace back to connections, not members. IS 800 covers bearing bolts, friction-grip bolts, and welds. For ordinary building work, snug-tight bearing bolts of property class 4.6 or 8.8 with E250 plates are the workhorse.
- Bolt shear, bolt bearing on the plate, and plate rupture must all be checked — the weakest link governs.
- Minimum pitch 2.5 × bolt diameter; minimum edge distances per Table 19.
- Fillet welds: design strength is based on the throat area at fu/(√3·γmw). Site welds carry the higher factor (1.5) for a reason — quality control.
Concrete or steel for a residential project?
For typical Indian homes, RCC remains the default: material availability, familiar labour, and fire/corrosion robustness. Steel wins where speed, long clear spans, or light foundations matter. Hybrid solutions — RCC frame with a steel stair, canopy or mezzanine — are common, and the interfaces between the two materials deserve the most design attention.
Frequently asked questions
Is IS 800:2007 still the current steel code?
Yes. IS 800:2007 remains the current general steel construction code in India (with amendments), and it uses the limit state method.
What steel grade is used for building structures in India?
Most rolled sections and plates are grade E250 conforming to IS 2062 (yield strength 250 N/mm²). Higher grades like E350 are common in pre-engineered buildings.
Why do steel beams need lateral restraint?
An unrestrained beam can twist and deflect sideways (lateral-torsional buckling) at a load well below its section strength. Connecting the compression flange to a slab, deck or purlins suppresses this and lets the beam use its full capacity.