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# RE: WT to HSS Out of Plane Moment Connection (Torsion??)

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: WT to HSS Out of Plane Moment Connection (Torsion??)
• Date: Wed, 17 Jan 2007 13:03:51 +1030

```At first reading I thought the question was about fastening to the face of a
HSS, and confirm that Blodgett has good coverage of connections.

But if I understand this structure correctly the beams are the same depth as
the HSS, the beams are cantilevers and the HSS is being used in torsion to
resist the fixed end moments (FEM's) of the cantilevers.

I don't know about anyone else but I was taught that it is poor practice to
have any part of a frame subject to torsion, no matter what the numbers say.
For normal bending there is a problem with flexural lateral-torsional
buckling, so to directly apply a torsion is asking for trouble. It is
generally considered good practice to design and detail so that direct
torsion is not present.

So have options:
1) frame cantilevers into columns with moment connection
2) provide counter acting backspan
3) provide knee-braces
4) could triangulate and provide tension cables above canopy, but these are
little use for wind uplift.

Basically need to get rid of the cantilever moment. From maximum shear
stress theory, the yield strength in shear is 50% of the yield strength in
tension, so using materials in shear is inefficient. The current beam is
subject to bending and torsional moments, bending produces extreme value
normal stresses in the outer fibres, torsional moments produce extreme value
shear stresses in the outer fibres. I don't know about US codes, but no
Australian code covers such a condition, so would need to check from first
principles. The expectation however is zero rotation at the cantilever
support, and it is unlikely that the torsional resistance of any section can
achieve this.

But maybe I misunderstood the description of the structure.

Regards
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
Roy Harrison & Associates
Consulting Engineers (Structural)
PO Box 104
Para Hills
SA 5096
South Australia
tel: 8395 2177
fax: 8395 8477

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Wednesday, 17 January 2007 11:44
To: seaint(--nospam--at)seaint.org
Subject: Re: WT to HSS Out of Plane Moment Connection

Jim,

You might try looking in Blodgett's book.  I seem to recall some sections
on welding a shear tab to the face of a HSS, which would be similar to
incorrectly.

Regards,

Scott

On Mon, 15 Jan 2007, Jim Lutz wrote:

> I am looking at a glass canopy which is cantilevered from a torsion
> beam. The glass canopy is supported on a series of parallel WT beams
> that frame into the long side of a rectangular HSS section which is
> supported at its ends. At the connection to the HSS, the WT has the same
> depth as the HSS, with the flange on top.  I have some intuitive
> concerns about local buckling of the HSS because the WT will be
> delivering the compression load over a narrow width into the bottom
> flange of the HSS, which is unstiffened. There is a little bit of design
> guidance for out of plane moment connections for HSS to HSS in the AISC
> Steel Specification, but I don't see anything that really applies to the
> situation I am looking at. Anybody got a good reference you can point me
> to? Oh yeah, and to make things more interesting, the WT's are skewed to
> the HSS.
>
> Jim Lutz, P.E., S.E.
>
>
>
> 720 3rd Avenue, Suite 1200
> Seattle, WA 98104-1820
> 206 505 3400 Ext 126
> 206 505 3406 (Fax)
>
>
>

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