Steel Solutions Center

7.2. Base Plates

7.2.1. How can one account for base-plate distortion due to welding?

When grouted, such curling or distortion is of no consequence. Otherwise (e.g., if leveling plates are used or if the base mates to a steel element), the gap allowance of AISC Specification Section M4.4 should not be exceeded. Additionally, see Specification Section M2.8, Finish of Column Bases.

7.2.2. When a steel base plate bears on less than the full area of concrete, the nominal bearing strength 0.85f'cA is multiplied by the lesser of 2 or the square root of the ratio of geometrically similar concrete area to base-plate area. Why?

The AISC Specification Section J8 is consistent with ACI 318 provisions, which recognize the increase in bearing strength that results from the confinement that is provided by the concrete surrounding that providing direct bearing resistance.

7.2.3. What are the preferred hole diameters in base plates?

The recommended maximum hole sizes for anchor rods in base plates are given in the AISC Steel Construction Manual Table 14-2. It is noted that these hole sizes permit a reasonable tolerance for misalignment in setting the bolts and more precision in the adjustment of the base plate or column to the correct centerlines. Note that these hole sizes are such that flame-cutting will often be required. An adequate washer (see 7.2.4) should be provided for each anchor rod. Because these hole sizes are recommended as maximum sizes, the use of smaller hole sizes is often justified if anchor-rod groups are set accurately.

7.2.4. What thickness and size of washer is required for the preferred hole diameters in base plates?

Recommended sizes for washers are provided in the AISC Steel Construction Manual Table 14-2.

7.2.5. When should grout holes be provided for base plates?

Grouting of base plates can be accomplished for common base-plate sizes without the need for grout holes. However, the use of a grout hole should be considered when the smaller side dimension of the base plate exceeds approximately 24 in. Two grout holes may be required for very large plates or long rectangular plates. See the discussion on grouting in Section 2.10 of AISC Design Guide 1: Base Plate and Anchor Rod Design (Second Edition).

[1] James M. Fisher and Lawrence A. Kloiber, 2006, Design Guide 1: Base Plate and Anchor Rod Design (Second Edition), AISC, Chicago, IL.


last updated 17 November 2020