Anchor Bolt / Foundation Bolt

An anchor bolt (also called holding-down bolt, HDB, or foundation bolt) is a steel bolt embedded in concrete to connect a steel structural member or equipment base plate to the foundation. The Indian standards governing anchor bolts: IS 5624:1993 (foundation bolts — specifications), IS 6133 (anchor fasteners with cement), IS 1367 (general fasteners), and the relevant IS 800:2007 design clauses for connection design.

Geometric configurations: (1) J-bolt — straight shank with a 180° bend at the bottom, providing mechanical anchorage in concrete; bent length typically 4-6 × shank diameter. (2) L-bolt — straight shank with a 90° bend at the bottom; used where headroom is limited. (3) Plate-anchor bolt — straight shank with a square or circular plate at the bottom, providing larger bearing area for high-uplift loads. (4) Hooked bolt — variant of L-bolt with a return bend. (5) Through-bolt — passes through the entire foundation slab and is anchored by a nut on the bottom face; used in pile caps and large foundations. The choice depends on uplift, shear, embedment depth, and concrete confinement.

Design per IS 800:2007 Cl. 10.4 + ACI 318 (Indian practice typically uses ACI for anchor design due to limited IS guidance): tension capacity governed by (a) bolt yield, (b) concrete cone breakout, (c) pull-out (for L-bolts and hooked bolts), (d) pry-out for short embedment. Shear capacity governed by (a) bolt shear, (b) concrete edge breakout, (c) concrete pry-out. Combined tension and shear via interaction equation. The most common Indian site issue is misalignment of anchor bolt template during foundation casting — bolts can deviate up to 25 mm from drawing, requiring oversized holes in column base plates. Pre-installation of templates (IS 5624 Cl. 5) and verification before pouring concrete are non-negotiable.