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WEDGE ANCHOR: A Type of Specialty Fastener

A wedge anchor is a type of specialty fastener used to attach objects to concrete or masonry structures. Wedge anchor may also be known as anchor bolt or expansion bolt in some areas.

A standard metal bolt makes up the base of the wedge anchor and is surrounded by a metal sleeve. Once an installer inserts the bolt into a masonry wall or floor, the base of the anchor slides up inside the sleeve. A rounded or conical tip on the end of the base forces the walls of the sleeve out to the side, where they grip the interior of the concrete or wall to form a secure hold.

Designers or Engineers must select each wedge anchor carefully based on several factors. They must consider the design action load that the anchor will need to support, as well as the composition and condition of the surface where it will be installed. Critical and minimum anchor spacing and edge distance should also be considered to justify the capacity of wedge anchor group installation. Everything from the length, diameter, the material of the anchor bolt, and base material compressive strength can impact the security of the installation that would require a load calculation for design verification. While standard installations are used in most applications, galvanized or stainless steel may be required in areas subject to frequent moisture or chemical exposure.

GENERAL 

An anchor can work properly only if it is correctly installed. The fixing thickness for suitable anchor length needs to be chosen so that the thickness of the non-bearing structure (plaster, insulation, etc.) and the fixture thickness are both complied with installation parameters to achieve secure tightening. The holes in the fixture should also conform to the standard (ref. ETAG Annex C, Table 4.1 – Diameter of clearance hole in the fixture) and these base plates do not undergo deformation under the load. This means that the base plate has to be rigid and fully placed against the base material. The washer should also be larger than the fixture hole.

DRILL BIT 

The drill bit diameter should be the same as the anchor diameter. Carbide-tipped masonry drill bits used for drilling holes for anchors should be checked to meet the dimensional requirements of the anchor manufacturers’ specifications. This means that especially the measurements and the concentricity of the tip need to be checked. Furthermore, all additional tools should conform to the manufacturer’s recommendations. To achieve the best performance of drill bits and to avoid possible damage, good condition and suitable hammer drill should always be used.

DRILLING 

A drill hole has to be at the right angle to the base material. Contractors can drill a hole that’s slightly longer than the anchor itself. It should be observed that reinforcement bars aren’t hit or drilled through to achieve the required anchorage depth. If reinforcement bars are hit, it could be possible that the load-bearing capacity of the fixing system is reduced or even the load resistance of the single anchor may be reduced. It is recommended to avoid contact with reinforcement bars and to abort the hole if contacted according to the design anchorage depth to place the anchors. The hole must be cleared of all dust and debris using a wire brush, compressed air, or vacuum after the drilling.

ANCHOR SETTING 

Before inserting the anchor into the hole, place the washer and nut on the anchor, then turn the nut a couple of turns. Not fully threading the nut protects the threads of the wedge anchor when hammering into the hole. Next, the entire unit must be inserted into the pre-drilled hole and carefully hammer the anchor’s dot point into each hole ensuring that the threads go below the surface of the concrete or past the edge of the fixture and that the minimum embedment is met. Once the washer’s face of the wedge anchor sits flush with the surrounding surface, use a wrench to tighten the nut 3-4 turns to hand-tight pre-position. It is recommended to use a torque wrench to ensure that the anchor has been installed correctly and tightened to the required torque value to draw up the anchor and fully expand the wedge sleeve and that sufficient force has been applied to ensure the fixing system will be safe.

OVERVIEW 

MASON Wedge anchor is an excellent choice when anchoring into solid concrete. These anchors have excellent holding values and are available in a range of materials to meet the requirements of many applications. It is important to make sure that the correct diameter and length are used in each application to ensure that the wedge anchor is set properly and safely.