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Re: Base Plate for Moment Frame-Shear Transfer

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For moment frame columns, there are a couple of primary mechanisms for transfer of shear, and the anchor bolts should be considered the least of them.  Anchor bolts may be adequate under small loads, but a 3/4" bolt with  1 1/2" of grout will fail at around 5 kips lateral force.
For intermediate level forces, the primary transfer of shear forces is developed through friction between the base plate and the grout / concrete developed from the overturning forces on the plate.  Consideration must be given to whether leveling nuts or leveling plates are employed during construction.  Additionally some would argue that the concrete encasement surrounding the column base provides a large measure of shear transfer through bearing as well.  The caveats with relying on friction transfer depend on the quality of the grout / grout placement, and the magnitude of the uplift forces.  What works in theory may not be realized in the field.
For large force transfer shear lugs are not un-common, but again proper grouting and quality control is critical.
AISC has some excellent publications regarding base plate design and considerations.  The steel design guide series volume 1 "Column base plates" should be considered a must for the office library.
----- Original Message -----
Sent: Thursday, August 22, 2002 11:27 PM
Subject: Base Plate for Moment Frame-Shear Transfer

A question came up today when designing a base plate for a steel moment frame which resists lateral forces.  We  are considering using a standard base plate with anchor bolts and 1 1/2" of grout.

How is shear considered to transfer from the base plate, through the grout bed and into the footing?  Do anchor bolts act in bending, or does grout adequately transfer the load thru interlock against steel and concrete.

Or, should a different method be considered, such as embedding the base of the column into the footing.

Thanks in advance...