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The Concrete Wedge Anchor

Purchase Wedge Anchors

The wedge anchor is installed through the fixture into a pre-drilled hole. As the anchor is hammered into the hole, the clip is recessed in the gap of the conical space, allowing the anchor to penetrate the hole. The anchor is set by tightening the nut. As the nut is tightened, the rod is pulled up, making the clip move outward on the tapered space, thus wedging it against the wall of the hole. The wedge anchor, once installed, cannot be removed without damage to the surrounding concrete.

The wedge anchor can only be used in solid concrete, and not in brick or block base material. The wedge anchor can be used in a variety of applications, from light duty to heavy duty. Some common applications for the wedge anchor are fastening pallet racks to concrete, installing a railing, mounting machinery to a floor, attaching framing to a concrete foundation..the list goes on and on.

Other common names for the wedge anchor are:

Stud Anchor Kwik-bolt Thunderstud®
DFS wedge anchor Kwik-bolt 2 anchor Sup-r-stud
Redi bolt Hilti Kwik bolt Concrete stud anchor
Wedge all Kwik bolt Stud wedge anchor
Kingpin Power bolt Stud anchor system
Trubolt Power stud  

Concrete wedge anchors can be made from carbon steel or stainless steel. The carbon steel wedge anchor can be zinc plated or hot-dip galvanized. Stainless steel wedge anchors are available in 303 or 316 stainless.

Zinc plated carbon steel wedge anchors are the most common. The wedge anchor, clip, nut and washer are all made from zinc plated carbon steel. Although the zinc plating offers some corrosion resistance, these wedge anchors are generally used for interior applications only. Also, the zinc plated wedge anchor is not accepted for use in ACQ treated lumber.

Hot dip galvanized wedge anchors offer the next level of corrosion resistance. Hot dip galvanized wedge anchors are suited for use in exterior applications where corrosion from water or moisture is a concern. They can also be used in ACQ treated lumber. The wedge anchor, nut, and washer are made from carbon steel that is then hot dip galvanized, and the clip is made from 303 stainless steel.

Stainless steel wedge anchors offer the highest level of corrosion resistance and can be used in exterior applications. Wedge anchors made from 304 stainless steel are resistant to many organic and inorganic chemicals, but should not be used in a saltwater environment. The anchor itself is made from 304 stainless steel, while the nut, washer, and clip are made of 18-8 stainless steel (which is comparable to 304 stainless steel.)  Wedge anchors made from 316 stainless steel offer the best corrosion resistance and can be used in the harshest environments, even salt water. All components of this wedge anchor are made from 316 stainless steel.

The wedge anchor is available in 9 diameters:  1/4", 5/16", 3/8", 1/2", 5/8", 3/4", 7/8", 1" and 1-1/4", and a wide range of lengths. Wedge anchors are also manufactured with different thread lengths. Some manufacturers prefer to offer a fully threaded wedge anchor, while others produce a partially threaded wedge anchor. There are pros and cons to both types of anchors and the question of which anchor is the better choice is still heavily debated among professionals in the industry.

The partially threaded wedge anchor is threaded for about a third of its length. The diameter of the unthreaded portion is less than the nominal diameter. The foremost benefit of the partially threaded wedge anchor is that it cannot be successfully installed in a hole that does not meet or exceed minimum embedment requirements.

Determining the size of wedge anchor required for your application is a fairly simple process. Anchor diameter required is typically dependent upon the hole in the fixture itself. The length of wedge anchor required simply add the thickness of the fixture to be fastened to the minimum embedment for the wedge anchor diameter being used, plus the thickness of the nut and washer (approximately equal to the anchor diameter itself). So, consider you have a 1-3/4" thick fixture with a 7/8" hole. As indicated by the chart below, that would require a 3/4" diameter wedge anchor. A 3/4" diameter wedge anchor has a minimum embedment of 3-1/4". The length needed is simply figured:

Thickness of Material (1-3/4")
+Minimum Embedment (3-1/4")
+Thickness of Nut/Washer (3/4")
=Minimum length of anchor (5-3/4")

Installation of the concrete wedge anchor is not a complicated process. It is helpful to note that hole diameter is always equal to anchor diameter, and, furthermore, hole tolerance is crucial to the wedge anchor's performance. To achieve the proper hole, it is important to use a hammer drill with a carbide-tipped masonry bit. These bits are specifically designed for use in hammer drills and meet the necessary ANSI standards.

The first step for installation is to drill your hole (at least 1/4" deeper than minimum embedment, accommodating a minor amount of concrete cutting which may not be able to be cleaned out of the hole), ensuring you meet the minimum embedment requirements for the diameter wedge anchor you are using. Minimum embedment is approximately 4-1/2 bolt diameters. Before drilling your holes, be certain to consider that no anchor should be placed any less than five anchor diameters from an unsupported edge, and no less than ten anchor diameters apart. The forces generated by the wedge anchor are transferred to the concrete — if they are placed too close together, holding values can be diminished, or the concrete may be damaged.

Mark From Up to, but not including Mark From Up to, but not including
A 1-1/2" 2" N 8" 8-1/2"
B 2" 2-1/2" O 8-1/2" 9"
C 2-1/2" 3" P 9" 9-1/2"
D 3" 3-1/2" Q 9-1/2" 10"
E 3-1/2" 4" R 10" 11"
F 4" 4-1/2" S 11" 12"
G 4-1/2" 5" T 12" 13"
H 5" 5-1/2" U 13" 14"
I 5-1/2" 6" V 14" 15"
J 6" 6-1/2" W 15" 16"
K 6-1/2" 7" X 16" 17"
L 7" 7-1/2" Y 17" 18"
M 7-1/2" 8"      

Wedge anchors are an excellent choice for anchoring into concrete because of their exceptional holding values. The holding power of any anchor is always dependent upon the quality or strength of the concrete itself. The holding values are also based on the depth of embedment - the deeper the embedment, the better the holding values. When comparing technical data for different manufacturers, it is important to determine what values are being given - ultimate load ratings or working load ratings. Either term is acceptable, but it is important that when comparing products, equivalent values be used.

      2000 PSI 4000 PSI 6000 PSI
Anchor Diameter (in.) Embed. Depth (in.) Torque Ft/Lb Tension (LB) Shear (LB) Tension (LB) Shear (LB) Tension (LB) Shear (LB)
1/4 1-1/8 5-10 1170 1443 1771 1813 2773 2635
1-3/4 1841 1443 2408 1813 2773 2635
2-3/4 1975 1443 2748 1813 2830 2635
3/8 1-1/2 25-30 1631 4318 3636 5121 4448 6232
3 3229 4318 5653 5121 5975 6232
5 4075 4318 6328 5121 6360 6232
1/2 2-1/4 50-60 3999 7419 6714 9377 9616 9888
4 6336 7419 8942 9377 10192 9888
6 6902 7419 10175 9377 12064 9888
5/8 3-3/4 75-90 4999 8264 8747 12928 9760 16373
5 8854 8264 15590 12928 19802 16373
7 9381 8264 16710 12928 17732 16373
3/4 3-1/4 150-175 6638 12504 11314 17050 16230 22965
6 10084 12504 18408 17050 21092 22965
8 11170 12504 19805 17050 22522 22965
7/8 3-7/8 200-250 8392 18250 16354 20234 16801 23980
5-3/4 12064 18250 18250 20234 23404 23980
8-3/4 12784 18250 16850 20234 25575 23980
1 4-1/2 250-300 9773 23617 18250 27605 27460 28909
7-1/2 11890 23617 26726 27605 34960 28909
10 15590 23617 30491 27605 37840 28909
1-1/4 5-1/2 400-450 17550 32275 22971 42690 32368 55566
7 21050 32275 27845 42690 48366 55566
10 27893 32275 34788 42690 61272 55566

Holding values shown above are ultimate holding values for the embedments shown. A safety factor of 4:1 (or 25%) is generally accepted as a safe working load. For example, if the ultimate shear load for a 1/2" dia. wedge anchor in 4000 psi concrete is 9377 lb., then the safe working load for that anchor is 2,344 lb. It is also important to remember that this value is the holding value for one anchor. If eight anchors will be used to anchor a fixture, the combined holding value would be 18,752 lb. (2,344 lb. X 8 anchors).

Although the wedge anchor can only be used in solid concrete, it is still a versatile anchor - available in a wide range of diameters and lengths and offered in zinc, hot-dipped galvanized and stainless steel for a variety of applications. This, combined with its exceptional holding values make the wedge anchor an excellent choice for most fastening jobs.

Purchase Wedge Anchors

Jan 13th 2009 Bob Carlisle

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