C-J9J9 Anchor rods and embedments
PDF page 577 · AISC 360-22
The term “anchor rod” is used for threaded rods embedded in concrete to anchor structural steel. The term “rod” is intended to clearly indicate that these are threaded rods, not structural bolts, and should be designed as threaded parts per Table J3.2 using the material specified in Section A3.4.
Generally, the largest tensile force for which anchor rods must be designed is that produced by bending moment at the column base and augmented by any uplift caused by the overturning tendency of a building under lateral load.
TABLE C-J9.1 Anchor Rod Hole Diameters, in
| Anchor Rod Diameter | Anchor Rod Hole Diameter |
|---|---|
| 1/2 | 1 1/16 |
| 5/8 | 1 3/16 |
| 3/4 | 1 5/16 |
| 7/8 | 1 9/16 |
| 1 | 1 13/16 |
| 1 1/4 | 2 1/16 |
| 1 1/2 | 2 5/16 |
| 1 3/4 | 2 3/4 |
| ≥ 2 | db + 1 1/4 |
TABLE C-J9.1M Anchor Rod Hole Diameters, mm
| Anchor Rod Diameter | Anchor Rod Hole Diameter |
|---|---|
| 18 | 32 |
| 22 | 36 |
| 24 | 42 |
| 27 | 48 |
| 30 | 51 |
| 33 | 54 |
| 36 | 60 |
| 39 | 63 |
| 42 | 74 |
Shear at the base of a column is seldom resisted by bearing of the column base plate against the anchor rods. Even considering the lowest conceivable slip coefficient, the friction due to the vertical load on a column is generally more than sufficient to transfer the shear from the column base to the foundation. The possible exception is at the base of braced frames and moment frames where larger shear forces may require that shear transfer be accomplished by embedding the column base or providing a shear key at the top of the foundation.
The anchor rod hole sizes listed in Tables C-J9.1 and C-J9.1M are recommended to accommodate the variations that are common for setting anchor rods cast in concrete. These larger hole sizes are not detrimental to the integrity of the supported structure when used with proper washers. The slightly conical hole that results from punching operations or thermal cutting is acceptable.
If plate washers are utilized to resolve horizontal shear, bending in the anchor rod must be considered in the design and the layout of anchor rods must accommodate plate washer clearances. In this case, special attention must be given to weld clearances, accessibility, edge distances on plate washers, and the effect of the tolerances between the anchor rod and the edge of the hole.
It is important that the placement of anchor rods be coordinated with the placement and design of reinforcing steel in the foundations as well as the design and overall size of base plates. It is recommended that the anchorage device at the anchor rod bottom be as small as possible to avoid interference with the reinforcing steel in the foundation. A heavy-hex nut or forged head is adequate to develop the concrete shear cone. See AISC Design Guide 1, Base Plate and Anchor Rod Design (Fisher and Kloiber, 2006), for design of base plates and anchor rods. See also ACI 318 and ACI 318M (ACI, 2019) and ACI 349 (ACI, 2013) for embedment design; and OSHA Safety and Health Regulations for Construction, Standards—29 CFR 1926 Subpart R—Steel Erection (OSHA, 2015) for anchor rod design and construction requirements for erection safety.