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RE: Concrete Strong Column/Weak Beam

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This calculation is simply a comparison of the flexural capacities of
the concrete SECTIONS to assure an appropriate mode of response.
Although member response can be more complicated, the check is really
intended to be a fairly simple calculation so it is based on the
section capacities.  For concrete sections M is always a function of P
but the effect is not significant for beams for which axial loads are
typically assumed to be absent.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Michael Valley, P.E., S.E.                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.              Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699      Fax:        -1201

-----Original Message-----
From: richard lewis [mailto:rlewistx(--nospam--at)juno.com]
Sent: Thursday, June 21, 2001 11:52 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Concrete Strong Column/Weak Beam


That is what puzzled me, "the flexural capacity of the columns is
affected by the coincident axial load".  Does it not matter how
slender a
column is when you check the flexural capacity based on the axial
capacity?

I take an interaction diagram, go up to the axial load and then go
across
to the curve boundary to find the moment capacity.  If it were a
column
design the moment capacity would be the magnified moment.  In this
check
it is just the moment capacity of the beam.

Rich


On Thu, 21 Jun 2001 10:16:41 -0700 "Mike Valley" <mtv(--nospam--at)skilling.com>
writes:
> Slenderness and P-delta do not play a part in this calculation.  The
> assumption is that flexural yielding will occur at every joint.
> The
> purpose of the calculation is to assure that the columns have
> sufficient flexural capacity to force yielding into the beams or
> girders.  Keep in mind that the flexural capacity of the columns is
> affected by the coincident axial load.
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> -
> Michael Valley, P.E., S.E.                   E-mail:
> mtv(--nospam--at)skilling.com
> Skilling Ward Magnusson Barkshire Inc.
> Tel:(206)292-1200
> 1301 Fifth Ave, #3200,  Seattle  WA 98101-2699      Fax:
> -1201
>
> -----Original Message-----
> From: richard lewis [mailto:rlewistx(--nospam--at)juno.com]
> Sent: Thursday, June 21, 2001 9:58 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Concrete Strong Column/Weak Beam
>
>
> I have a question regarding using ACI 21.4.2.2 check for the strong
> column weak beam check.  How is column slenderness accounted for in
> this
> check.  The ACI equation is :
>
> sum Me >= (6/5) sum Mg
>
> If I have a slender column, is Mg magnified somehow like in ACI
> 10.13.3?
> If I used a P-Delta analysis to get Mg, does it have to be
> magnified
> for
> this equation?  How does the effective length factor 'K' factor
> into
> this
> check?
>
> Rich


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