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RE: torsional property "C" as listed in 'aisc hss connection man ual'

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Title: RE: torsional property "C" as listed in 'aisc hss connection manual'
Ooops! Forgive me for not actually reading the message thoroughly enough before responding to see that you are actually making the plate girder into a box section. {-:
 
C for your box shape can be calculated as 2 times the wall thickness times the area enclosed by the box, measured to the centerlines of the bounding elements. There is a figure in the design guide I gave the link to below, but basically the bounded areas can be calculated as (depth minus average flange thickness) times (width minus average thickness of enclosing plates). Since your flanges are probably thicker than your webs, I'd take the smaller thickness in the calculation, since the shear will be evenly distributed around the periphery of the box. Any elements of the cross section that are not part of the box don't participate and shouldn't be counted.
 
Charlie
-----Original Message-----
From: Charlie Carter [mailto:carter(--nospam--at)aiscmail.com]
Sent: Monday, June 19, 2000 8:24 AM
To: 'seaint(--nospam--at)seaint.org'
Cc: 'Brian Sielaff'
Subject: RE: torsional property "C" as listed in 'aisc hss connection manual'

>In order to have better torsional resistance from a steel girder, curved in
>plan, I am trying to use a wide flange section with side plates (thus
>converting it into a box section). I plan to follow the same procedure given
>in AISC HSS connection manual. However, while computing equivalent torsional
>properties of this built-up section, I do not find any procedure to
>calculate 'torsion property C' as listed in pages 1-12 thru 1-55 of AISC
>manual. Does anyone know how to calculate 'C' value of a built-up section?

No. C is a torsional property that is unique to closed cross sections, since it is a function of the area enclosed by the cross section. A W-shape or plate girder does not enclose any area, and therefore cannot have a property such as C for HSS.

Open cross sections behave differently (they have both pure torsion and warping torsion). For detailed information on this, see AISC Design Guide No. 13, Torsional Analysis of Structural Steel Members.

    https://www.aisc.org/publications/shop.asp?action="">

Charlie