"Stiffeners" at torsional connection
"Stiffeners" at torsional connection
(OP)
Have a torsional connection at the top of a concrete footing (supporting a relatively light item with a lot of surface area). Therefore, wind is my evil loading...See attached sketch.
Torsional moment is 9.5 k-ft - not large, but trying to get an estimated weld length has been difficult. The only way around it, that I could see, was to flare "stiffeners" from the HSS section to get the required weld length.
Basically (3) things I am unsure of:
1. Now that I have introduced these elements, is it even worth checking their capacities? If yes, is there a rational procedure floating around? My intuition says this small loading can be handled by inspection with not much additional analysis.
2. I am concerned that as the HSS begins to torque there will be an uneven distribution of stress in the welds, maybe causing the 'front-loaded' welds to crack. Any ideas in configuring this connection in a different manner?
3. I can't find a prequalified weld between the HSS and the base plate. The closest I could find was a flared weld, but it didn't show the HSS bearing on the plate to be welded to.
Torsional moment is 9.5 k-ft - not large, but trying to get an estimated weld length has been difficult. The only way around it, that I could see, was to flare "stiffeners" from the HSS section to get the required weld length.
Basically (3) things I am unsure of:
1. Now that I have introduced these elements, is it even worth checking their capacities? If yes, is there a rational procedure floating around? My intuition says this small loading can be handled by inspection with not much additional analysis.
2. I am concerned that as the HSS begins to torque there will be an uneven distribution of stress in the welds, maybe causing the 'front-loaded' welds to crack. Any ideas in configuring this connection in a different manner?
3. I can't find a prequalified weld between the HSS and the base plate. The closest I could find was a flared weld, but it didn't show the HSS bearing on the plate to be welded to.
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RE: "Stiffeners" at torsional connection
RE: "Stiffeners" at torsional connection
BA
RE: "Stiffeners" at torsional connection
renderu: That is a thought. I am trying to be economical as well, as the work is for a nonprofit group.
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RE: "Stiffeners" at torsional connection
RE: "Stiffeners" at torsional connection
At the moment, I am wait to hear if we can get rid of the beam in torsion and extend the vertical members (not shown) into the footings. That option is highly dependent on the displays, as they have already been constructed by the artist.
Do you see an option that avoids the stiffeners?
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RE: "Stiffeners" at torsional connection
RE: "Stiffeners" at torsional connection
If you want to stiffen the HSS, use a cap plate on the end.
BA
RE: "Stiffeners" at torsional connection
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
BA
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
BA
RE: "Stiffeners" at torsional connection
Look again. 1.392DL for 1/2" weld would be 1.392*8L or 11.1kips per inch length of weld. D is given as the number of sixteenths in the diameter, so 1/2" is 8 sixteenths.
BA
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
With strength design in the US, a 70 ksi fillet 70ksi weld is good for 1.392 kips per 1/16". I am guessing a7x mixed up 1/2" in the denominator with 8 (for 8/16=1/2").
For a 1/16" fillet weld Φ0.6 FexxAw = 0.75(0.6)(70)(0.0625)/sqrt(2) = 1.392 kips.
If the applicable code allows, a flare bevel groove weld (with reinforcing fillet if need) may work.
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
D is given as the number of sixteenths in the weld size, so 1/2" is 8 sixteenths.
BA
RE: "Stiffeners" at torsional connection
RE: "Stiffeners" at torsional connection
I agree that a direct weld is a possibility, but my preference would be to use angles each side, bolted to the foundation.
BA
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
Nonprofit structures act essentially the same way as full paying clients structures act, and they require the same full attention to detail and design and cost. You mean the 5x5 tube is being twisted about its own axis, with a torque T = 9.5 ft.kips? Put a 1/2 or 5/8" end plate on the tube, 6" high and 6" wide at the top, and 14 or 15" wide a its base, at the base plate. Center four A.B’s. on either side of this end plate, two on each side of the HSS. If you wish put another plate 5" wide x 12" long under the tube and atop the main base plate with a couple A.B’s. in it to guard against the tube acting as a 4' long lever arm against lateral loads.
RE: "Stiffeners" at torsional connection
I am having a hard time visualizing your idea at this time in the night. I will try again in the a.m. =)
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RE: "Stiffeners" at torsional connection
Also, do you truly have a force couple creating this moment, or is there an uplift component as well? In other words, is this a 1k load, 9.5ft away pushing up or something similar? This matters, because not only do you have to account for the moment, but the uplift as well.
-5^2 = -25
http://www.eng-tips.com/supportus.cfm
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
Forgive me for bugging you, but I am VERY curious as to how this thing is loaded in pure moment. Can you expound on that? I'm having trouble seeing how a setup like this can be loaded in such a way...
-5^2 = -25
http://www.eng-tips.com/supportus.cfm
RE: "Stiffeners" at torsional connection
In Russia building design you!
RE: "Stiffeners" at torsional connection
Then that 5x5 tube has a small vertical cantilever load on it, mostly just DL; it has a lateral canti. load on it, (wind load)(face area on 1.5 to 2 face areas); plus the torsional load you have been talking about. All a vibrating and potential fatigue mess back at the conc. pier. And, if it is someplace where a 300# drunk can try to chin himself, don’t forget that. Quite a different problem than what you have been talking about.
RE: "Stiffeners" at torsional connection
Fatigue from wind on a structure like this? That seems like an unreasonable amount of analysis. The curb surrounding the displays is not mountable, and I think the lateral component is negligible in this case: I can't see 500 lbs of lateral load doing much to affect any interaction equations.
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