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The situation is a steel baseplate that has to be anchored to concrete to resist lateral loads.

base plate with 8 holes

The lateral load on the base plate is great enough that more than one or two anchor rods are required. The base plate has room for 8 anchor rods.

The holes in the base plate will be somewhat over-sized per AISC to aid in setting the base plate over over the anchor rods. The anchor rods have already been cast into the concrete. The nuts on the anchor rods will not be tightened enough to consider the connections to be slip-critical. There will be some movement of the base plate required before it engages the anchor rods.

Variations in the placement of the anchor rods and the hole locations will mean that not all of the anchor rods will be engaged at the same time.

In this situation, how do you determine how many anchor rods can be considered to be effective in resisting the load? The number of anchor rods will directly effect the size of each anchor rod.

Air
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hazzey
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1 Answers1

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This report (large PDF warning) on base plate design says that the AISC Steel Design Guide I instructs the use of plate washers fillet welded to the top of the base plate, with the inner diameter of the washer being much closer to the rod diameter, to ensure initial engagement of the rod. Specifically, I found that information in Sections 2.3.2 (pp.8-10), 3.3.1.2(p.21), and a visual example in Figure 3.9.

While that doesn't directly answer your question, it seems the answer is "You can't determine that, so we put in other design elements to account for it."

Trevor Archibald
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