Mechanical anchors are devices used to give fasteners a firm grip in a variety of materials, where the fasteners by themselves would otherwise have a tendency to pull out.
Anchors can be classified in many ways by different manufacturers. In this unit, anchors have been divided into five broad categories:
• One-step anchors
• Bolt anchors
• Screw anchors
• Self-drilling anchors
• Hollow-wall anchors
One of the most common anchors in frame construction is the anchor bolt.
Anchor bolts are used to anchor the sill plate to the concrete foundation.
The anchor bolt is set into the wet concrete. The sill plate is then placed over the anchor and a nut and washer are used to secure the sill plate to the foundation.
The sill plate acts as a base for the wall framing.
One-step anchors are designed so that they can be installed through the mounting holes in the component to be fastened. This is because the anchor and the hole into which the anchor is installed have the same diameter.
Various Types of Anchors
Click on each to find out more:
A. Wedge Anchors:
Wedge anchors are heavy-duty anchors supplied with nuts and washers. The drill bit size used to drill the hole is the same diameter as the anchor.
Stud Bolt Anchors
A. Stud Bolt Anchors:
Stud bolt anchors are heavy-duty threaded anchors. Because this type of anchor is made to bottom in its mounting hole, it is a good choice to use when jacking or leveling of the fastened component is needed.
B. Sleeve Anchors:
Sleeve anchors are multi-purpose anchors. Tighten the anchor nut or screw to expand the anchor and tighten it in the hole.
C. One-piece Anchors:
One-piece anchors are multi-purpose anchors. They work on the principle that as the anchor is driven into the hole, the spring force of the expansion mechanism is compressed and flexes to fit the size of the hole.
D. Hammer-Set Anchors:
Hammer-set anchors are made for use in concrete and masonry. There are two types of hammer-set anchors: nail and screw. An advantage of the screw-type anchors is that they are removable.
E. Bolt Anchors:
Bolt anchors are designed to be installed flush with the surface of the base material. They are used in conjunction with threaded machine bolts or screws. In some cases, they can be used with threaded rod drop-in, and single- and double- expansion anchors.
Drop-in, and Single- and Double Expansion Anchors
Drop-in anchors are typically used as heavy-duty anchors. There are two types of drop-in anchors. The first type is made for use in solid concrete and masonry.
Single- and double-expansion anchors are made for use in concrete and other masonry. The double-expansion anchor is used mainly when fastening into concrete or masonry of questionable strength.
F. Screw Anchors:
Screw anchors are lighter-duty anchors made to be installed flush with the surface of the base material. They are used in conjunction with sheet metal, wood, or lag screws.
G. Self-Drilling Anchors:
This fastener has a cutting sleeve that is first used as a drill bit and later becomes the expandable fastener itself.
Guidelines for Drilling Anchor Holes
Drilling Anchor Holes in Hardened Concrete or Masonry
When installing anchors and/or anchor bolts in hardened concrete, make sure the area where the equipment or component is to be fastened is smooth so that it will have solid footing. Uneven footing might cause the equipment to twist, warp, not tighten properly, or vibrate when in operation.
The next slide presents an example of a typical procedure used to install many types of expansion anchors in hardened concrete or masonry.
Click on each button to find out more:
Step 1: Drill the anchor bolt hole the same size as the anchor bolt. The hole must be deep enough for six threads of the bolt to be below the surface of the concrete. Clean out the hole using a squeeze bulb.
Step 2: Drive the anchor bolt into the hole using a hammer. Protect the threads of the bolt with a nut that does not allow any threads to be exposed.
Step 3: Put a washer and nut on the bolt. Tighten the nut with a wrench until the anchor is secure in the concrete.
Hollow-wall anchors are used in hollow materials such as concrete plank, block, structural steel, wallboard, and plaster. Some types can also be used in solid materials.
a. Toggle Bolts:
Toggle bolts are used to fasten equipment, hangers, supports, and similar items into hollow surfaces such as walls and ceilings. They consist of a slotted bolt or screw and spring-loaded wings.
b. Wall Anchors:
Sleeve-type wall anchors are suitable for use in plywood, wallboard, and similar materials. The two types of wall anchors are standard and drive.
The standard type is commonly used in walls and ceilings and is installed by drilling a mounting hole to the required diameter.
The drive-type anchor is hammered into the material without the need for drilling a mounting hole.
• Wallboard anchors are self-drilling medium- and light-duty anchors used for fastening in wall board.
• Metal drive-in anchors are used to fasten light to medium loads to a wallboard.
Epoxy Anchoring Systems
Epoxy resin compounds can be used to anchor threaded rods, dowels, and similar fasteners in solid concrete, hollow walls, and bricks.
For one product, a two-part epoxy is packaged in a two-chamber cartridge that keeps the resin and hardener ingredients separated until use.
This cartridge is placed into a special tool similar to a caulking gun. When the gun handle is pumped, the epoxy resin and hardener components are mixed within the gun; then the epoxy is ejected from the gun nozzle.
Using Epoxy Anchoring Systems
To use epoxy to install an anchor in solid concrete, you have to:
1. Drill a hole of the proper size in the concrete.
2. Clean it using a nylon (not metal) brush.
3. Dispense a small amount of epoxy from the gun to make sure that the resin and hardener have mixed properly (this is indicated by the epoxy being of a uniform color).
4. Place the gun nozzle into the hole, and inject the epoxy into the hole until half the depth of the hole is filled.
5. Push the selected fastener into the hole with a slow twisting motion to make sure that the epoxy fills all voids and crevices, then set it to the required plumb (or level) position.
6. After the recommended cure time for the epoxy has elapsed, tighten the fastener nut to secure the component or fixture in place.
Using Epoxy Anchoring Systems
The procedure for installing a fastener in a hollow wall or brick when using epoxy is basically the same as the one just described. The difference is that the epoxy is first injected into an anchor screen to fill the screen, then the anchor screen is installed into the drilled hole.
Use of the anchor screen is necessary to hold the epoxy intact in the hole until the anchor is inserted into the epoxy.