IS 4000 provides comprehensive guidelines for the design, assembly, and tightening of high-strength friction grip (HSFG) bolts in steel structures. It covers critical parameters like slip factors for various faying surfaces—including the effects of hot-dip galvanizing—and standardizes installation methods such as the turn-of-nut and calibrated torque control techniques.
Specifies requirements for hot-dip galvanized coatings on fasteners.
Quick Reference Values
minimum bolt tension0.85 times the proof load
slip factor clean mill scale0.33
slip factor sand blasted0.48
slip factor hot dip galvanized0.10
hole clearance up to 24mm bolt2 mm
hole clearance above 24mm bolt3 mm
Key Formulas
P_s = μ × n × P_o — Slip resistance capacity of joint (μ = slip factor, n = interfaces, P_o = minimum bolt tension)
Practical Notes
Never reuse fully tensioned HSFG bolts; they must be discarded once tightened to their minimum bolt tension.
Faying (contact) surfaces must be strictly free of dirt, oil, paint, or loose scale, as these severely reduce the slip factor and compromise joint capacity.
Standard hot-dip galvanized surfaces significantly lower the joint's slip factor (down to ~0.10) unless properly treated (e.g., light grit blasting or wire brushing) before assembly.