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[SEAOC] [SEAOC] 9" Anchor Bolt Embedment -Reply

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The anchor bolt length was increased in response to the common
problems observed after the Northridge Earthquake.

An unfortunate, but very common construction sequence used by
builders of residential buildings constructed on slab foundations is to use
a two pour sequence.  The footings are poured first, causing a
horizontal construction joint to be formed at the slab to footing interface.
This joint must be clean and free of sand and debris before the slab
concrete is poured if  good shear transfer is occur.   This does not
happen as building inspection can not assure this without being at the
site during the pour.  Sliding of slabs and sand pockets were observed in
many instances.  The additional length of the anchor bolts as well as the
decrease in spacing to four feet is expected to provide significant
enough doweling action to prevent slip from occurring, and prevent
concrete pop outs at the footing edge due to shallow embedment
(approx 1 inch) into the footing at the construction joint.

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