Clause 5.4.1 specifies the partial safety factors (γm) for material strength in limit state design. These factors account for material variability, manufacturing tolerances, and the consequence of failure. They are applied to characteristic strength values to obtain design strength.
Key Requirements
•γm0 = 1.10 — for resistance governed by yielding (tension yielding, beam bending, local buckling)
•γm1 = 1.25 — for resistance governed by ultimate stress (net section rupture, bolt failure, weld failure)
•γmw = 1.25 — for shop welds; 1.50 for site welds (as per some interpretations and Annex F)
•γmb = 1.25 — for bolts (shear, bearing, tension)
•These factors are used in the denominator: Design strength = Characteristic strength / γm
Reference Tables
Table 5 — Partial Safety Factors for Materials (Clause 5.4.1)
Description
γm
Value
Resistance governed by yielding
γm0
1.1
Resistance governed by ultimate stress
γm1
1.25
Resistance of connection — shop fabrication
γmf
1.25
Resistance of connection — site fabrication
γmf
1.25
Resistance governed by buckling (bolts)
γmb
1.25
γm0 = 1.10 is used for yielding checks (tension on gross section, beam moment, compression). γm1 = 1.25 is used for fracture/rupture checks (net section, bolt shear/tension).
Formulas
Design Strength = (Characteristic Strength) / γm
General formula for obtaining design strength from characteristic strength using partial safety factor
γm = Partial safety factor for the relevant failure mode (γm0 or γm1)
Practical Notes
✓The ratio γm1/γm0 = 1.25/1.10 = 1.136 means that failure modes involving fracture (net section rupture, bolt failure) carry a 14% higher safety margin than yielding modes.
✓In practice, γm0 = 1.10 gives an effective factor of safety on yield of about 1.10 × 1.5 (load factor) ≈ 1.65 against working loads — comparable to the old working stress method FOS.
✓Unlike IS 456 where γc = 1.50 for concrete, IS 800 uses γm0 = 1.10 for steel — reflecting the more controlled manufacturing quality of structural steel compared to concrete.
Common Mistakes
⚠Using γm0 = 1.10 for net section rupture check — rupture is governed by γm1 = 1.25, not γm0.
⚠Applying partial safety factors to loads instead of material strength — load factors (γf) are separate and specified in IS 800 Table 4.
⚠Using γm1 for beam bending capacity — bending (yielding of cross-section) uses γm0 = 1.10.