The wedge anchor can only be used in solid concrete. Wedge anchors are designed not to be used in other masonry materials such as brick or hollow block. The expansion clip on the wedge anchor is placed on the anchor body in a manner and location that makes the expansion tolerance location critical. This critical tolerance location of the expansion clip allows for the wedge anchor to be used only in a solid base material such as concrete. Wedge anchors are sometimes used in solid base materials other than concrete such as natural stone. They may work in this type of base material, but the holding values are not tested because each natural stone is different and inconsistent.
Wedge anchors derive their holding values through expansion against the base material. The expansion is created through mechanical means once the anchor is inserted into the hole in the concrete. The mechanical expansion of the wedge anchor is produced once the anchor is inserted into the hole in the concrete and the nut is turned clockwise. Turning the nut clockwise pulls the anchor body up through the nut, which makes the expansion clip slide down the cone-shaped, necked down a portion of the anchor body and expands the clip against the wall of the concrete and the wedge anchor body.
The expansion of the wedge anchor creates forces upon the concrete that must be taken into consideration when using wedge anchors. The distance between wedge anchors and the distance from an unsupported edge of the concrete is critical. Both of these distances are critical because the expansion forces created are cone shaped and the expansion cone of one anchor that overlaps with the cone of another will decrease the holding values of both anchor or one anchor if it is placed too close to an unsupported edge.
Generally, the spacing requirements used by the concrete anchor industry are that the anchors should be spaced a minimum of 10 anchor diameters away from each other and a minimum of 5 anchors from an unsupported edge of the concrete. Spacing closer will cause a decrease in holding values or there may not be any holding values at all.
The thickness of the concrete that the wedge anchor is placed into is critical because each diameter of wedge anchor requires a minimum embedment. For the wedge anchor to reach its minimum holding values in concrete, it must be set in the concrete at a minimum distance below the surface of the concrete. The thickness of the concrete is thick enough to allow the anchor to be placed so that minimum embedment is reached. The wedge anchor must also be placed so that it is no closer than 1.5 diameters from the unsupported side of the concrete.
Wedge anchors are manufactured from different materials that are used in different applications. Different types of wedge anchors should be used when they will be installed in different environments. A difference between the different types of wedge anchors is their ability to resist rusting. The zinc plated wedge anchor should be used in a dry environment where no moisture is present. In an environment where moisture is present, the wedge anchor that is hot-dipped galvanized should be considered. The 303 or 304 stainless steel wedge anchor should be installed if it will be submerged in water. In applications where the wedge anchor will be submerged in water and in certain chemicals such as chlorine, the 316 stainless steel wedge anchor should be used.
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully. Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications. This article is meant to serve only as a basic explanation of concrete fasteners. Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.