Last reviewed 16 Sept 2026 · 6 min read
Steel as a structural material
Advantages: very high strength-to-weight ratio; ductile (large deformation before failure, good for earthquakes); uniform, reliable properties; fast construction with prefabricated members; easy to modify, strengthen, dismantle and recycle; long spans with slender members.
Disadvantages: corrosion (needs painting/galvanising and maintenance); loses strength at high temperature (needs fire protection — strength falls sharply above about 400–500 °C); buckling of slender members and thin plates; fatigue and brittle fracture under certain conditions; higher material cost per tonne.
Mechanical properties
| Property | Value for structural steel |
|---|---|
| Modulus of elasticity | N/mm² |
| Shear modulus | N/mm² |
| Poisson's ratio (elastic) | 0.3 |
| Unit mass | 7850 kg/m³ |
| Coefficient of thermal expansion | /°C |
Grades (IS 2062)
| Grade | Yield stress (N/mm²), thin sections | Ultimate stress (N/mm²) |
|---|---|---|
| E250 (Fe 410) | 250 | 410 |
| E300 | 300 | 440 |
| E350 | 350 | 490 |
| E410 | 410 | 540 |
| E450 | 450 | 570 |
Yield stress reduces somewhat for thicker sections. Sub-qualities A, BR, B0, C indicate impact toughness requirements (for welded and low-temperature applications).
Rolled sections
| Section | Designation (Indian practice) | Typical use |
|---|---|---|
| Beams | ISLB, ISMB, ISWB, ISHB (light, medium, wide flange, H) | Beams, columns |
| Columns | ISHB, ISSC | Heavy columns |
| Channels | ISJC, ISLC, ISMC | Purlins, built-up members, lintels |
| Angles | ISA (equal and unequal) | Truss members, bracing, connections |
| Tees | ISNT, ISHT | Truss chords |
| Plates, flats, strips | ISPL, ISF | Built-up girders, gussets |
| Tubes / hollow sections | CHS, RHS, SHS (IS 4923, IS 1161) | Trusses, columns, space frames |
Example designations: ISMB 300 @ 44.2 kg/m (depth 300 mm); ISA 75×75×8 (equal angle, legs 75 mm, thickness 8 mm). Parallel flange sections (IS 12778 / NPB, WPB) are also rolled.
IS 800:2007 — design philosophy
IS 800:2007 uses limit state design (working stress design is retained in a separate section). The structure must satisfy the limit states of strength (collapse, buckling, fracture, fatigue, overturning, sliding) and serviceability (deflection, vibration, corrosion, fire).
Partial safety factors for materials ()
| Resistance governed by | Symbol | Value |
|---|---|---|
| Yielding | 1.10 | |
| Buckling | 1.10 | |
| Ultimate stress (rupture) | 1.25 | |
| Bolts (bearing type) and rivets | 1.25 | |
| Friction grip (HSFG) bolts — slip resistance | 1.10 (shop and field when slip at serviceability) / 1.25 (at ultimate) | |
| Welds | 1.25 shop, 1.50 field |
Partial safety factors for loads ()
| Combination (strength) | Dead | Imposed — leading | Imposed — accompanying | Wind or earthquake |
|---|---|---|---|---|
| DL + LL (+ crane load) | 1.5 | 1.5 | 1.05 | — |
| DL + LL + WL/EL | 1.2 | 1.2 | 1.05 | 0.6 (1.2 when wind/EQ is the leading load) |
| DL + WL/EL | 1.5 (0.9 where dead load is beneficial) | — | — | 1.5 |
For serviceability the factors are 1.0 on each load, except that with dead + imposed + wind together the imposed and wind loads take 0.8.