Desinging Weld for Torsional Loading
Desinging Weld for Torsional Loading
(OP)
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 ?
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 ?





RE: Desinging Weld for Torsional Loading
Look on this link it gives C for various rectangular sections:-
http://ww
desertfox
RE: Desinging Weld for Torsional Loading
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.
RE: Desinging Weld for Torsional Loading
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:-
ht
desertfox
RE: Desinging Weld for Torsional Loading
This might be easier to read:-
http://ww
desertfox
RE: Desinging Weld for Torsional Loading
Thanks...makes more sense now.
RE: Desinging Weld for Torsional Loading
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.
RE: Desinging Weld for Torsional Loading
Your welcome
desertfox
RE: Desinging Weld for Torsional Loading
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
RE: Desinging Weld for Torsional Loading
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.
RE: Desinging Weld for Torsional Loading
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.
RE: Desinging Weld for Torsional Loading
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.
ht
If you can upload a picture or sketch for your situation I may be able to help further.
desertfox
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
I can't see it, the image is to large ie file to big.
Can you sketch it with some dimensions on?
desertfox
RE: Desinging Weld for Torsional Loading
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.
RE: Desinging Weld for Torsional Loading
files to large to open and to give advice on stresses i will need dimensions
can you make the files pdf's
desertfox
RE: Desinging Weld for Torsional Loading
ht
Do a search for welds.
http
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
This file works out the equivalent fillet weld for the "U" shape to give the same weld area as the existing "L" shape,
the new fillet weld 0.227" however I suggest you round it up to 0.25".
We need to analyse the loads next, but I am unsure from your drawings the orientation of the load and also how it can be typically in 9 positions round the hole?
I will assume a single unity load acting at the hole running parallel to the 2" thick strip at the 5.5" distance as given on the original sketch.
desertfox
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
Nice job, if you look round the site you will find tables for "I" beams, channels,angles etc.
There is a lot of other good engineering info there to.
regards
desertfox
RE: Desinging Weld for Torsional Loading
Here is a calculation for the old and new weld stresses.
I used unity load because you didn't specify one, but you can see your new arrangement uses half the weld size but is under less stress than the old one assuming of course the load case I chose is correct.
Let me know what you think.
desertfox
RE: Desinging Weld for Torsional Loading
Design assumption, since all 9 pipe support plates are welded up identically, must be that the load is shared equally at all 9 bolted points, or that it's easier/better to make one common part than it is to individually calculate each plate and each weld.
RE: Desinging Weld for Torsional Loading
What is the orientation of the load as we look at your plan view? I assume the load is going into the paper but whats its magnitude?
I have calculated that your new arrangement only needs to have a quarter fillet weld as opposed to the half inch previously.
Are the calcs of any use to you.
desertfox
RE: Desinging Weld for Torsional Loading
Well if I am right about the direction of the load then the calc's I posted need the load turning through 90 degrees and the welds need to be stressed for bending not torsion, would you agree?
desertfox
RE: Desinging Weld for Torsional Loading
You are looking horizontally into one end of the machine casing. The weight (load) on these nine pipe supports is a circular 6" diameter pipe ring with a large number of equally spaced nozzles (small flex hose connections) spaced all the way around. So dynamic loads are equal everywhere around the circle, but were probably considered very low compared to the weight of the pipe assembly itself. (Reasonable, a small diameter flex hose will not transmit much force to its nozzle.)
Dead weight loads are "down" - towards the bottom of the image.
The dead weight was probably were considered equally divided among the nine bolted pipe supports, but since each acts vertically on each bolt at each pipe support, each weld is stressed at a different angle at each of the nine. Since weld and each pipe support plate is detailed identically, somebody apparently just figured stresses out once.
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
Thanks for the stars guys.
Well I think your worst case situation for the welds is the one I have detailed, where the component weight acts at 5.5" from the bolt hole vertically down creating torsion and direct shear but I could be wrong.
Not sure I agree that the weight of the pipe is equally shared amongst nine supports as they will always be some slight variation in the manufacture which destroys the symmetry. Indeed just looking at the sketch of the pipe supports they are not spaced symmetrical, one half of the pipe as four supports the other five and only one support is on the horizontal centre line.
I think if it were my problem I would design the support such that if I had all the weight hanging off one or two of those supports it would do the job, then the additional supports would be belt and braces.
I agree racookpe that whatever component weight hangs off the supports each of the welds is loaded differently.
desertfox
RE: Desinging Weld for Torsional Loading
I agree, the bolts would not have identical load if the supports are non-symmetrical. But you are quite conservative on only one or two out of 9 supports work scenrio, a huge safety factor for static pipe support.
I think a SF of 2 should satisfy most environment.
RE: Desinging Weld for Torsional Loading
Each time I encounter this type of data, I convert it to the format that was attached. I use the first column as a dropdown list to VLOOKUP in the sorted data. I add the index to convert it back, in the event I have to add or remove something.
Dik
RE: Desinging Weld for Torsional Loading
RE: Desinging Weld for Torsional Loading
Yes sorry it wasn't done intentional,but racookpe1978 had a situation very close to yours with torsional stress on weld,I suppose he felt it was related which in truth it was.
regards
desertfox
RE: Desinging Weld for Torsional Loading
Did you ever get your welding for torsional loading problem resolved? Or, are you just complaining about your thread being hijacked to be difficult. I hesitate to tell you what Blodgett is talking about, on pg. 7.4-6, because I thought I told you never to bring the subject up again, in public.
Blodgett's books and papers are sometimes a little bit difficult to follow, he was a bit short on explanation at times, his notation was lacking at times, some publishers might have done a little classier job of proof reading or exact technical review before printing, but the books would not have been as inexpensive either, and they sure contain a wealth of good info. I knew him pretty well and he was an amazingly intuitive guy on welding, weldment design and your kind of problem. For what he had to work with, he certainly boils the problems down to the basics, but could be quite theoretical too, when the problem called for it.