Stud Concrete Anchor Bolts
Published by Robert Carlisle on Feb 23rd 2011
A stud concrete anchor bolt is a concrete anchor that, once installed into the concrete, has a threaded portion sticking up out from the concrete. Stud concrete anchor bolts are manufactured from standard carbon steel that is zinc plated or hot-dipped galvanize. It can also be made from stainless steel in grades 303/304 or 316. One end is threaded and the other end is necked down by a permanently attached steel clip. Stud concrete anchor bolts are packaged with the correct number and size of nuts and washers. The common generic name for a stud concrete anchor bolt is the wedge anchor.
Concrete Anchor Bolt Diameter
Stud anchor bolts range in size from 1/4” for light duty applications to 1-1/4” diameters for heavy-duty type applications. The diameter chosen for any particular application depends on the holding value requirements, on the specifications and on the hole diameter in the fixture being fastened.
Concrete Anchor Bolt Length
Each diameter of stud anchor bolt comes in a number of different lengths. The length of stud anchor bolt selected will depend on the embedment depth and the thickness of the material being fastened. To determine the minimum embedment depth, add the thickness of the material being fastened to the minimum embedment for the diameter of stud anchor bolt being used plus the thickness of the nut and washer.
The minimum embedment for each stud anchor diameter can be found at /wedge-anchor-technical-specifications
The hole diameter drilled into the concrete for a stud anchor bolt is equal to the diameter of stud anchor bolt being installed. The hole must be drilled using a carbide bit that meets ANSI standards. Hole tolerance is critical when installing a stud anchor bolt. Using an ANSI standard bit will ensure match tolerance between hole diameter and stud anchor bolt anchor diameter. The hole must also be drilled using a hammer drill set in the hammer mode to ensure hole tolerance for the stud anchor bolt.
Depth of Hole
The depth of the hole in the concrete for the stud anchor bolt must be a minimum of 1/2” deeper than the stud anchor bolt will penetrate the concrete. This extra space at the bottom of the hole ensures that the stud anchor bolt will not bottom out before it is embedded into the concrete at the proper distance. This extra depth also allows space into which the concrete dust created during the installation process will fall, which will ensure effective installation of the stud anchor bolt.
Stud anchor bolts are manufactured from four different types of materials or coatings:
• Zinc plated carbon steel – used for indoor applications where moisture is not present.
• Hot-dipped galvanized – used for outdoor applications where moisture is present.
• 303/304 stainless steel – used for outdoor applications submerged in water.
• 316 stainless steel - used for outdoor applications submerged in water and in other liquid chemicals, such as chlorine.
Each diameter of stud anchor bolts has an embedment depth that the stud anchor bolt must be inserted and installed at to achieve minimum holding strength. Deeper embedment will usually result in better holding values. The rule of thumb regarding stud anchor bolts is that the deeper the embedment then the better the holding strength. Embedding a stud anchor bolt too deep into the concrete may be difficult because rebar in the concrete may get in the way.
The thread length on different manufactured stud anchor bolts varies. Some stud anchor bolts have partial threads while others have full threads. Full threaded stud anchor bolts allow for the stud anchor bolt to be installed at less than minimum embedment depths if the user is not very careful. Partially threaded stud anchor bolts cannot be installed at less than minimum embedment depth, but the threads may not be long enough for shimming or leveling of the fixture.
Type of Threads
All stud anchor bolts utilize national coarse threads and are designated by the number of threads per inch. For example, the 1/2” –13 stud anchor bolt has 13 threads per inch and will accept any threaded item that has the same type of threads.
Stud Concrete Anchor Bolt Installation
- Drill a hole in the concrete using a hammer drill in the hammer mode. Use a carbide tipped drill bit that meets ANSI standards with the same diameter as the stud anchor bolt being installed.
- Make sure that the depth of the hole is drilled to a minimum of 1/2” deeper than the stud anchor bolt will penetrate the concrete and that the embedment depth meets the minimum embedment depth requirements for the diameter of stud anchor bolt being installed.
- Clean the hole of all dust and debris created during the drilling process by using a wire brush, vacuum or compressed air.
- Place the washer on the threaded end of the stud anchor bolt and then thread the nut on until the top of the nut is level with the top of the threads. This will protect the threads of the stud anchor bolt during installation.
- Insert the stud anchor bolt through the hole in the fixture and into the predrilled hole in the concrete, or insert directly into the predrilled hole in the concrete.
- Strike the nutted end of the stud anchor bolt with a hammer until a minimum of 6 threads is below the surface of the concrete or the fixture being attached.
- Using fingers, tighten the nut to finger tight.
- With a wrench, turn the nut clockwise 2 to 3 turns or until the required torque values are reached.