Types of Anchors for Anchoring to Concrete - Hilti

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1.5 Traditionally, design engineers specify cast-in-place anchors if they know beforehand where anchors are to be installed. Headed Bolt L-Bolt J-Bolt Stud-welded Plate FIGURE 2. Cast-in-place Anchors Many of these types of anchors have special uses. Shear lugs and stud-welded plates provide large shear resistance, while channel bars give specific attachment capability. J and L bolts are typically used for anchoring sill plates to foundations, but have a tendency to straighten and pull out under high tension loading. Headed bolts under ASTM A 490 and F 1554 specifications are veritable workhorses for structural engineers. But what if the cast-in-place anchor is mislocated, or if the location of the anchor is not known before construction, or additional anchorages need to be made after the concrete is cast? The post-installed anchor industry has developed a wide variety of products for these situations. POST-INSTALLED ANCHORS With the development and improvements of rotary hammer drills and carbide-tipped bits, the user has the capability to install many different kinds of post-installed anchors in hardened concrete virtually anywhere that is accessible to the drills. Post-installed anchors can be divided into two major types, depending on the method of transferring load into the concrete. They are mechanical systems and bonded or adhesive systems. Anchors can also be cross-classified according to their load carrying capability; heavy-duty, medium-duty and lightduty. Table 2 provides an overview of the major types of post-installed anchors currently available as well as a generalized load categorization. Table 2. Post-Installed Anchors MECHANICAL SYSTEMS HEAVY- MEDIUM- LIGHT- DUTY DUTY DUTY Undercut Anchors • Torque-controlled expansion anchors Heavy duty sleeve anchor • • Wedge anchors • • x Coil anchors • • x Screw anchors • • • Sleeve anchors • • Light duty metal anchors • Plastic anchors • Displacement-controlled expansion anchors Drop-in x • x Self-drilling x • x BONDED OR ADHESIVE SYSTEMS Using threaded rods or reinforcing bars Capsule systems • • x Cartridge systems • • x Bulk-injection systems • • x Cemetitious or epoxy grouted systems • • x • Indicates normal category x Indicates possible but not primary category MECHANICAL ANCHORING SYSTEMS While mechanical anchors have been available for several decades, there have been significant advances in the types and capabilities of these systems. They cover the range from heavy duty to light duty capacities. The major concern is to select the appropriate anchors that will resist the expected loads for the given application. Is the anchor expected to experience seismic or fatigue loads, or merely static loads? While some anchors will withstand all of these types of loads, others may fail abruptly under dynamic loading at a load level less than the static capacity. ■ UNDERCUT ANCHORS These anchors have been on the market for about 20 years. They are excellent for use under both static and dynamic loads. They obtain their holding capacity through keying, that is, direct bearing on the concrete, and, under proper installation, can withstand very high loads without slipping out of the drilled hole. They are the preferred anchors for use where cracks in tension zones of the concrete can be expected to occur.
■ EXPANSION ANCHORS Expansion anchors have been available for at least 30 years. There are two basic types that are distinguished by their operating principles. The first, torquecontrolled expansion anchors, are installed by inserting the anchor into the drilled hole, and applying the prescribed setting torque to the head or nut. A cone at the bottom of the anchor is pulled up into an expansion sleeve that expands into the concrete with local crushing, and providing both friction and localized keying as load-transfer mechanisms. Most have a beneficial follow-up expansion characteristic that under tension loading, the more the anchor bolt displaces upward out of the hole, the greater the expansion forces. There are several types available that vary significantly in their ability to resist static and dynamic loads. The heavy-duty sleeve anchor (not to be confused with the light duty sleeve anchor composed of a sheet metal sleeve around a cone) can resist dynamic loads as well as function well in expected cracks in concrete. Wedge anchors are the most common type of torque-controlled expansion anchor. Many have been tested for resisting seismic loads and have received ICBO ES Evaluation Report listings for such service. Sleeve anchors are generally considered light duty, and rely more on friction and less on local crushing and keying of the concrete. They can be used in hollow masonry. The second major type of expansion anchor is the displacement-controlled expansion anchor. Two primary examples are the drop-in and the self-driller. Drop-in anchors are installed in the predrilled hole by use of a setting tool that drives a plug into the expansion portion of the anchor. The lower section of the anchor is expanded into the concrete, which experiences local crushing. The second type has cutting teeth on the lower end and drills its own hole. The anchor is driven onto an expansion plug that expands the lower portion of the anchor into the concrete. These anchors derive their holding capacity from friction and keying. The drawback is that they do not have any follow-up expansion. Once set, they do not expand further under loading. If the plug is not Sleeve Anchor FIGURE 3. Mechanical Anchors Torque-controlled Expansion Anchor sufficiently set, the anchor may experience reduced capacity. ■ OTHER TYPES OF MECHANICAL ANCHORS Screw anchors of smaller diameters and used for light duty applications have been available for many years. They are installed into holes drilled with matchedtolerance bits. Recently, manufacturers have been introducing larger diameter screw anchors in the heavy-duty range, either installed into holes drilled with matched-tolerance bits or using bits meeting the requirements of ANSI B212.15. They distribute the load into the concrete through load transfer from the threads to the concrete (keying). Coil anchors have also been introduced into the market in the heavy-duty Heavy-duty Sleeve Anchor Undercut Anchor Drop-in Anchor Self-drilling Anchor Stud Anchor FIGURE 4. Displacement-controlled Expansion Anchors load range. A coil anchor is composed of a coil near the end of a specially designed lag bolt. As the bolt is torqued, the screw advances through the coil, which expands into the concrete. High load capacities can be developed. ■ LIGHT DUTY ANCHORS There are many light duty anchors available, made of metals and plastics. They function in a variety of base materials, concrete, masonry, wood, drywall, etc. Manufacturers publish test data to document their capacities in these base materials. BONDED ANCHOR SYSTEMS Bonded resin or adhesive anchors were generally introduced into the construction market about twenty years ago.
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Types of Anchors for Anchoring to Concrete - Hilti

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