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Re: FW: Compression Capacities for WFs with Webs Not Compact

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Curt,

I 'll look into it. Thanks

Sam


On Tue, 11 Jan 2005 11:57:34 -0500, LaCount, Curt
<Curt.LaCount(--nospam--at)jacobs.com> wrote:
> Sam,
> 
> It looks to me like you are using f=36 ksi in equation A-B5-12.  The value
> should be the computed elastic stress, which in this case is limited by
> column buckling to 7.13 ksi.  At that stress, there is no reduction for be.
> 
> I hope that helps.
> 
> Curt La Count
> Jacobs Engineering
> Portland, OR
> 
> 
> -----Original Message-----
> From: Szuchuan Chang [mailto:szuchuan(--nospam--at)gmail.com]
> Sent: Monday, January 10, 2005 8:28 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Compression Capacities for WFs with Webs Not Compact
> 
> Hi,
> 
> I am reviewing an existing building with LRFD steel design.  Along the
> drag lines of a roof diaphragm are the existing W14x22 beams that
> suppose to pass on the collected diaphragm shear to the brace frame at
> the end of the building.  I am treating these beams as compression
> members just to see if it can take the loads to the brace frame.
> (Ignore bending for the moment.)
> 
> Fy=36 ksi;
> bf/2tf of the W14x22 is 7.46 which meets the flange compactness of 15.9;
> h/tw of the W14x22 is 53.3 which is bigger than the compactness of 42.3;
> assuming the beam is braced at 15 feet along the weak axis.
> Kl/r = 173.1;
> Table 3-36 on the manual page 16.1-143 give phi*Fcr = 7.13 ksi.
> area = 6.49 sq in
> Pall (without reducing for no-compact web) = 7.13*6.49 = 46.3 kips
> 
> To account for the reduction on the effectiveness on the web,
> I apply the Eq A-B5-12 on pg 16.1-91
> (using b=13.7 & t=0.23)
> I get "b sub e" = 10.2 inches.
> 
> I than reduce the cross section area form 6.49 - 0.23*(13.7-10.2) =
> 5.69 sq inches
> 
> The new capacity I got is reduced to 40.5 kips.
> 
> Question? Am I doing this correctly?
> 
> Thanks
> 
> Sam
> 
> 
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