Expansion Anchor / Chemical Anchor
Post-installed anchors in hardened concrete
Expansion anchors are mechanical fasteners that expand into a drilled hole in concrete, providing tension and shear resistance through interference fit. Used for connecting structural elements (steel members, equipment) to concrete after construction. Per IS 5624:1993 (foundation bolts) + Indian common practice referencing ACI 318 + ICC-ES (Evaluation Service Reports), expansion anchors are widely used in Indian construction for retrofit, equipment installation, and architectural attachments.
Main types: (1) Wedge anchor — most common; cylindrical body with wedge that expands when nut tightened. Capacity 8-50 kN tension; 5-30 kN shear. (2) Sleeve anchor — sleeve splits as bolt is tightened, gripping concrete. (3) Drop-in anchor — internally threaded; bolt inserted later. (4) Through-bolt — passes through entire member. (5) Chemical anchor — epoxy/acrylic resin; higher capacity than mechanical. Major Indian suppliers: Hilti, Sika, Bostik, Fischer, Pidilite ChemiAnchor, Wurth.
Design considerations: (a) Concrete edge distance ≥ 2× anchor diameter; anchor spacing ≥ 6× diameter. (b) Drilling depth ≥ specified embedment; deeper for higher capacity. (c) Concrete strength M25 minimum recommended; lower grades reduce capacity. (d) Anchor type — chemical for highest capacity, mechanical for routine. (e) Test loading — proof loading at 1.5× design load before commissioning. The most-overlooked aspect: edge distance and anchor spacing. Many Indian retrofit installations have inadequate spacing (4× diameter instead of 6×), causing premature concrete-cone breakout failure. Always specify minimum edge and spacing per ACI 318 / manufacturer.
- Equipment attachment to concrete (machinery, electrical)
- Steel-to-concrete retrofit connections
- Architectural attachments (cladding, signage)
- Renovation and partial demolition
- Pre-cast concrete connections