Hilti HUS3 Concrete Screw
Hilti HUS3 is a mechanical concrete screw anchor for the post-installed fixing of light to medium structural and non-structural elements to concrete substrates. The anchor is a self-tapping concrete screw, supplied in standard diameters of 6 mm to 14 mm and lengths from 35 mm to 230 mm, with a hexagonal or countersunk head depending on application. Installation is by drilling a pilot hole sized to the screw diameter, brushing and blowing the hole clean, and driving the screw with an impact driver until the head bears on the fixture. The anchor develops capacity by mechanical interlock between the screw thread and the surrounding concrete, with no chemical adhesive required. HUS3 holds European Technical Assessment (ETA) approval for cracked and uncracked concrete with C1 seismic approval, and is supplied in galvanised, mechanically galvanised and stainless steel variants for varying exposure environments. TRSC specifies HUS3 for the post-installed fixing of light steel framing, services penetrations, balustrade brackets, mechanical equipment supports, and other applications where the load case is in the medium range and the installation cost per anchor is the controlling commercial consideration. The product's removability and re-installability are valued where temporary or relocatable fixings are required.
Hilti HUS3 is TRSC's default mechanical concrete screw specification for medium-load post-installed fixing where the engineering action is governed by mechanical capacity rather than the deep-embedment or full-capacity reinforcement requirements that drive injection adhesive specification. The product is selected over alternatives (Hilti HSL3 sleeve anchor, Ramset Trubolt+, Powers Spit-Lok drop-in anchor) on three grounds: (1) installation speed — concrete screws install in approximately 30% of the time of equivalent-capacity sleeve or wedge anchors, which controls labour cost on production-anchoring work; (2) removability — the screw can be removed and re-installed without compromising substrate integrity, which is valued for temporary or relocatable fixings (mechanical equipment that may be relocated, fitout elements with future change planned); (3) low edge distance and spacing — the HUS3 has lower minimum edge distance and inter-anchor spacing requirements than equivalent-capacity expansion anchors, which permits installation in confined or congested substrate conditions. The most common specification pitfalls TRSC encounters in the field are: (1) over-torquing — the screw must be driven until the head bears firmly on the fixture but no further; over-torquing strips the thread engagement in the concrete and reduces the anchor capacity; the contractor's impact driver must be set to the manufacturer-published torque and verified against a hand torque wrench at agreed inspection frequency; (2) hole diameter — the pilot hole must be sized to the manufacturer's published diameter for the screw size; oversized holes reduce thread engagement and oversized drill bits are a common contractor substitution that invalidates the design; (3) seismic application — HUS3 holds C1 seismic approval but the design loads are reduced from the static design loads under the ETA seismic provisions; engineers must confirm the seismic-design load is checked against the ETA seismic capacity table rather than the static capacity table. TRSC anchor specifications include the product nomination, the screw diameter and length, the embedment depth, the design load and seismic loads where applicable, and the substrate edge distance and inter-anchor spacing requirements.