Rarely is a concrete project completed without using temporary or permanent anchoring systems. Anchors range in size from 1/4- to 1 1/2-inch-diameter and embedment depths of 2 to 6 inches. Manufacturers specify allowable loads for each anchor. Besides load capacity, you must consider other factors when choosing the most economical anchoring system. LOADING When choosing the best anchor for each project, consider the applied loading. Shear, tension, or combined shear-tension may be applied as a static, dynamic, or impact load. The most common static load is produced by the weight of materials, the dead load. Dynamic or vibratory loading is most commonly associated with machine anchors. An impact is a shock load. ANCHOR SYSTEMS The four major anchor groups are expansion, wedge, undercut, and chemical. 1. Expansion: This type of anchor provides frictional resistance by side hole contact applied from the expanding action of shields or wedges. 2. Wedge: Like the expansion anchors, wedge anchors rely on side frictional resistance; however, the way they achieve this resistance is different. Wedge anchors have soft metal sleeves that expand and conform to drill hole irregularities. 3. Undercut: Undercut anchors don't rely on friction to transfer the applied load to the concrete. Instead, the anchor bears directly against an undercut in the concrete, transferring the applied load by compression. 4. Chemical: Forces are transferred by chemical bond from the anchor into the surrounding concrete.