Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

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

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Conrad,
The reason HSS(Hollow Structural Section) is being used is that it is torsionally strong. However your comments pointed out one problem and that is the WT is the same depth as the HSS. This makes for a lot of welding at the flanges of the HSS which are round. The welders have to be specifically qualified for that flare bevel weld--at least here they do. Of course the designer's intention might be to try and get the forces at the extremities of the WT into the flanges of the HSS. If I were facing this problem, I would try to get
(1) the HSS deeper to make the welds easier or
(2) the WT shallower but heavier to achieve the same effect and/or
(3) reinforce the HSS web with a thickener plate to avoid oil-canning of the HSS wall or (4) add a small length of flange on the bottom of the WT to make it a W again to spread the forces
Just some thoughts for your and Jim's consideration.
Gary

Conrad Harrison wrote:
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
Steven CONRAD Harrison
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
your situation.  I will admit, however, that I could be remembering
incorrectly.

Regards,

Scott
Adrian, MI


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)




******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********