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Re: Transfer of Load from Column to Footing?

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Is this a case where plain structural concrete may be used for capacity requirements? If the pier counts as a pedestal (h/d < 3), Eq 22.5.5 of ACI 318 allows the use of bearing capacity for the pedestal, or 0.85fc' * A where A is the larger of the bearing area or SQRT(A.pedestal/A.bearing) < 2 if the "supporting surface is wider on all sides than the loaded area."

That seems almost automatically good, since I do a bearing capacity check under all baseplates anyway.

At 03:33 PM 10/29/2004 -0400, you wrote:
For columns, ACI requires 1%xAg of the concrete column for vertical reinforcement. Then there's the minimum 1/2%xAg for dowel reinforcement between the column/footing interface. The compression development length of this 1/2%xAg sometimes controls the footing thickness. My questions are as follows:

1. Does this apply to short piers where you have a steel column on a 36" or less pier? I often have piers that are around 24" tall to get the bottom of the footing below the frost line. This height does not allow proper compression development length for the dowel bars into the pier, let alone a compression splice lenghth.

2. Where Moments are induced into the footing, I embed and size the anchor rods to develop the tensile forces applied to the anchor rods. In a short pier, if 1%xAg is used for the vertical reinforcement, the pier's height can not adequately provide a development length in tension for the vertical reinforcement. Can I embed every vertical bar into the footing with a standard hook and make sure the hook is developed in tension? I realize this is pain to build but with a short pier, what are the options?

3. The is the allowable reduction factor of A-required/A-provided. In most cases, the minimum 1%xAg requirement is much larger than what is required by design. Can I count on this?

Thanks.
--Daniel E. Boltz, P.E.




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