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Re: Shear strength of concrete members

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It sounds like the column is shear critical which means that the column
will never reach its ultimate flexure capacity.
If you are doing a seismic evauation of a concrete building I would
definately recommend that you get a copy of ATC40.  You should also get
FEMA 273.  Between these two documents it should be able to answer most of
your questions.

>I am currently involved in a seismic evaluation of a 50 year old
>concrete structure.  Due to the inadequate shear reinforcement
>detailing, I have run into an issue that seems to have very little
>research/documentation.  The issue is the shear strength of a member
>(columns which are not part of the primary lateral force resisting
>system in this case) without shear reinforcement when the member has
>reached it's flexural capacity.
>'Reinforced Concrete Structures' by Park and Pauley has a brief
>section discussing shear at plastic hinges.  The section suggests that
>once the flexural reinforcement has yielded that the crack widths are
>such that very little shear can transfer by aggregate interlock or
>dowel action.  Therefore, the shear must be transferred across the
>compression zone.  This means that the bd term (shear area) that
>appears in all shear capacity equations would result in an
>unconservative value for the shear strength of the concrete.
>I would appreciate any input on this issue, specifically the shear
>area once the member has reached it's ultimate capacity.
>George Barclay, P.E.