Desinging Weld for Torsional Loading 2

[Stillerz]

I am trying to design welds for torsional loadings (twisting) on HSS.
I am using Blodgett's procedure for welds treated as lines.
Table 4 on page 7.4-6 of Blodgett has the equation for the force on the weld for "twisting" as:

f=T*C/Jw

Jw can readily be determined from table 5 on pg. 7.4-7 for HSS.

My question is, how does one determine "C" for a rectangular HSS ?

 

[desertfox]

Hi Stillerz

Look on this link it gives C for various rectangular sections:-

http://www.roymech.co.uk/Useful_Tables/Sections/RHS_cf.html

desertfox

 

[Stillerz]

Desert-
I am not sure that is the "C" I am looking for.
That "C" also appears in the AISC manual.
in looking at Blodgett's sketch, it appears the "C" in the equation is more like the "C" you typically see in
f=MC/I for bending stress.

 

[desertfox]

Hi Stillerz

Okay in that case then you want the distance from the centroid of the weld to one corner of the box ie the diagonal distance look at this link and see the examples:-

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html#Design_St

desertfox

 

[desertfox]

Hi Stillerz

This might be easier to read:-

http://www.utm.edu/departments/engin/lemaster/Machine Design/Lecture 34.pdf

desertfox

 

[Stillerz]

desert-
Thanks...makes more sense now.

 

[cntw1953]

stillerz:

In general, the torsional stress in a closed shape is proportional to wall thickness and distance from load center. Let me know if it is not.

 

[desertfox]

Hi Stillerz

Your welcome

desertfox

 

[GregLocock]

" torsional stress in a closed shape is proportional to wall thickness...Let me know if it is not. "


It isn't in the usual case and I'm struggling to think when it would be.




Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[cntw1953]

Greg:

I have some reservation on my own wording too.
If you have ROAK's FORMULA for Stress and Strain, please see CH 9, case 16 under Table 20 - Formulas for Torsional Deformation and Stress (mine is 6th ed).

Please comment after reading. Thanks.

 

[racookpe1978]

Thank you D.Fox - That seems to come close to a problem I've got.

Trying to convince my ozz to redesign a cantilevered beam weld holding a 6" cooling water pipe inside a generator frame.

Now, he is using a "L-shaped notch" (welded all around with 1/2 fillets) to connect a beam to a massive (2" thick generator frame member.

To save time for a welder working inside the generator after the copper and laminations have been installed, I want to re-design the joint so I can use a smaller (faster to weld) fillet that will need to be longer, and change the "L-shaped notch" to a "U" that will be deeper and have a longer moment arm.

How do I prove the longer moment arm will yield less weld metal required?

What is the economical balance between a longer thinner fillet and a much thicker fillet that can be shorter in length? Clearly, the same ultimate strntgh will be required.

 

[desertfox]

hi racookpe1978

I can't quite visualise your set up however if you go on the Roymech site link and scroll up you will see propeties of welds as lines for bending and direct loading.

http://www.roymech.co.uk/Useful_Tables/Form/Weld_strength.html#Design_St

If you can upload a picture or sketch for your situation I may be able to help further.

desertfox

 

[racookpe1978]

Sketch coming. Thank you.

 

[racookpe1978]

See sketch of current configuration here: he is calling for a total of ten linear inches of 1/2 fillet.

 

[desertfox]

Hi racookpe1978

I can't see it, the image is to large ie file to big.
Can you sketch it with some dimensions on?

desertfox

 

[racookpe1978]

Proposed U-Shaped notch, with longer 4" legs on each side of the 2" thick rib.

A bit heavier, but these things aren't going anywhere, and there are no interferences in this area that I need to worry about clearing. The notch could even be deeper, if that would help.

 

[desertfox]

Hi again racookpe1978

files to large to open and to give advice on stresses i will need dimensions

can you make the files pdf's


desertfox

 

[unclesyd]

You might want to look at the following.

http://www.steeltools.org/STEELTOOL...umentKey=67849ca7-7a49-4c4c-84d2-ac55fa5ebeac

Do a search for welds.

http://www.steeltools.org/STEELTOOLS/STEELTOOLS/Resources/SearchLibrary/Default.aspx

 

[racookpe1978]

In pdf format.

 

[racookpe1978]

Suggested geometry, with longer weld but greater moment arm.