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

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Thanks Gary

I understand that HSS are torsionally strong, but down here we would still
have concerns about using the torsional strength as the primary means of
support. (Also the authorities down here are especially critical and
sensitive about structures covered in glass in public spaces.)

However, compared to the USA and UK, we don't really have any substantial
HSS, so the possibility of finding one suitable for use as a torsion beam is
relatively remote. Also our codes have no rules for checking torsion. The
design manual written to the code does provide guidance but it is still from
a perspective of torsion as a secondary effect being induced by poor or
unavoidable detailing issues. So there is obviously some traditional
opposition to it! From a Mechanical perspective torsion is the nature of the
game, and there are some huge machines, so it is something that can be dealt
with.

So if no one else has concerns about using a torsion beam, and it is common
practice with proven history of success, I guess I have nothing to be
concerned about. More over it opens up new possibilities for future
projects, assuming I can find a suitable section, and get anyone to go along
with the idea.

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: Gary L. Hodgson and Assoc. [mailto:ghodgson(--nospam--at)bellnet.ca] 
Sent: Wednesday, 17 January 2007 23:31
To: seaint(--nospam--at)seaint.org
Subject: Re: WT to HSS Out of Plane Moment Connection (Torsion??)

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)
>>
>>
>>
>>     
>
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