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RE: K factor Approximation for Trussed Girders

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Thanks for the response.

I agree that it's odd- but the trusses were not designed to take anything
but gravity loads and the columns are designed for the smallest allowable
DL+LL forces.  I've had to look at the allowable live load reductions to get
the columns to work for gravity load alone.  All the connections are simple
riveted connections and there is not nearly enough block wall to transfer
the lateral loads via shearwall.

I looked at the old steel code (Forth Edition AISC)and I see what they
probably designed the columns for (there was no k factor in the design of
columns then, just l/r),  but even using a k=1, there is not nearly enough
moment capacity to transfer the wind load (which was 20PSF back then).

I'm just going to reccommend adding a few braced bays here and there and try
to stiffen up these frames to get them to work.

Brian S. Bossley, EIT
Ventura Engineering
7610 Olentangy River Rd.
Columbus, OH 43235
(614) 847-1110 x121


-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
Sent: Monday, June 28, 2004 12:36 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: K factor Approximation for Trussed Girders


Brian,

>From what you describe, you can use a lower K value.  I do find it curious
that a structure constructed in 1947 has no lateral force resisting system.
It may not be what it needs to be for current code requirements, but there
should be something resisting the lateral loads for over 50 years.
Regards,
Harold Sprague

>From: "Brian S Bossley" <bsbossley(--nospam--at)venturaengineering.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: K factor Approximation for Trussed Girders
>Date: Thu, 24 Jun 2004 13:54:55 -0400
>
>Fellow engineers:
>
>I am trying to analyze a frame that was built in 1947 and was never
>considered to take lateral load.  I noticed that if I use a k = 2, the
>existing column will not support half of the weight that it currently
>should under just DL+LL.  The girders framing into the column are trusses.
>I can get an approximate I for the truss based on the stiffness of the
>truss.  Can I use a lower k value based on the I/l ratios of the truss
>girder -vs- the wide flange column?
>
>Brian S. Bossley, EIT
>Ventura Engineering
>7610 Olentangy River Rd.
>Columbus, OH 43235
>(614) 847-1110 x121
>

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