STEEL

HSFG Bolt (High-Strength Friction-Grip)

Pre-tensioned high-strength bolt transferring load by friction, not bearing

Also calledHSFG bolthigh strength friction grip boltslip critical boltfriction grip connectionpretensioned bolt
Related on InfraLens
CODES
IS 4000IS 3757
Definition

A High-Strength Friction-Grip (HSFG) bolt is a high-tensile bolt (to IS 3757) that is tightened to a controlled high pre-tension so the clamping force it induces lets the connection transfer shear by friction between the faying (contact) surfaces rather than by the bolt bearing on the plate. Designed and installed per IS 4000, the connection is 'slip-critical': it does not slip into bearing under service loads, giving a stiff, no-slip, fatigue-resistant joint.

HSFG connections are used where slip is unacceptable — bridges and structures under fatigue/load reversal, crane gantries, high-stiffness moment connections and oversized/slotted-hole situations. Their performance depends critically on achieving the specified bolt pre-tension (by torque control, turn-of-nut, or load-indicating washers) and on the slip factor of properly prepared faying surfaces (clean, unpainted or with an approved high-friction coating). They are costlier than ordinary bolts and demand controlled installation and inspection, so they are specified deliberately, not by default.

Where used
  • Fatigue/load-reversal connections (bridges, gantries)
  • Slip-critical + high-stiffness moment connections
  • Connections with oversized/slotted holes
  • Seismic + dynamically loaded steel joints
  • No-slip splice + bracing connections
Acceptance / threshold
Bolts to IS 3757, connection designed + installed per IS 4000: specified pre-tension achieved (torque/turn-of-nut/DTI) and verified, faying surfaces prepared to the design slip factor; slip + bearing + tension checks satisfied.
Frequently asked
How does an HSFG bolt work?
It is tightened to a high controlled pre-tension; the clamping force creates friction between the contact surfaces that transfers shear, so the joint does not slip into bearing — a stiff, fatigue-resistant slip-critical connection (IS 4000).
When are HSFG bolts used instead of ordinary bolts?
Where slip cannot be tolerated — fatigue/load-reversal members, bridges, crane gantries, high-stiffness moment connections and slotted/oversized-hole joints. They cost more and need controlled installation and inspection.
Related terms
Base Plate
Steel plate at the bottom of a column transferring axial load to concrete. Thickness governed by bending under bearing pressure.
Bolted Connection
Joining steel members with bolts; checked for shear, bearing + tension
Stiffener
Plate welded to steel beam web preventing buckling. Required at supports and points of concentrated load.
IS 1786 — Parts List (High Strength Deformed Steel Bars)
Complete list of all 1 parts of IS 1786 — high strength deformed steel bars.
Welding (Steel Joining)
Per IS 816 (manual) and IS 9595 (welding procedure)
Shear Stud / Shear Connector
Welded stud transferring horizontal shear between steel beam and concrete slab in composite construction.
Yield Strength (fy)
Stress at which steel begins permanent deformation. Common Indian rebar grades: Fe415, Fe500, Fe550, Fe550D.
Lintel
Horizontal beam over a door/window opening transferring wall load above to side walls. Min bearing 150 mm each side.
fy (Yield Strength of Steel)
415/500/550 N/mm² for Fe415/500/550
Development Length / Anchorage
Length of bar embedment to develop full strength