×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

"Stiffeners" at torsional connection

"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.

In Russia building design you!

RE: "Stiffeners" at torsional connection

I would assume all torsion is taken up at the first stiffeners. Now it's simple.

RE: "Stiffeners" at torsional connection

You said it was a torsional moment, but your double headed arrow shows otherwise. If it is a torsional moment, the arrow should be pointing along the axis of the HSS. Using the right hand rule, the thumb points in the direction of the arrow and the fingers point in the direction of the moment. Please clarify.

BA

RE: "Stiffeners" at torsional connection

(OP)
BA: Yes, I oriented the arrow incorrectly.

renderu: That is a thought. I am trying to be economical as well, as the work is for a nonprofit group.

In Russia building design you!

RE: "Stiffeners" at torsional connection

I think my suggestion is economical. You could do a calc on my assumption within, at least an hour. Trying to figure out the stresses going on in your arrangement is complicated. Material for the extra gussets is small. Labor would be an extra hour or so. You probably spent that much just posting and discussing the problem on this forum. If you're not charging then that's all good. How many of these are you constructing? Just one? That's important also.

RE: "Stiffeners" at torsional connection

(OP)
renderu: I agree it is complicated. If I could find a way to avoid the use of those stiffeners, it would be good - there are four of them at the moment (two displays, two per display). My time spent is immaterial as it is a 'not-to-exceed' LS - I expect to spend some personal time on more interesting projects.

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?

In Russia building design you!

RE: "Stiffeners" at torsional connection

I don't have any specific advice on the arrangement at this moment. I don't have that reference info at home. Torsion in welds and in non-continuous (open) sections is tricky. I would need to go back to my textbook. But it is ultimately simple.

RE: "Stiffeners" at torsional connection

You could weld the HSS directly to the plate. M= 9.5'k = 114"k. It requires 114/5 = 22.8k each side. That is probably not an approved welding procedure, so use a connector plate each side of the HSS about 6" long . Fillet weld to the HSS and the base plate as required.

If you want to stiffen the HSS, use a cap plate on the end.

BA

RE: "Stiffeners" at torsional connection

I agree with BAretired, partly. Except that I would consider the peak stress at the start of the weld. I would need to think about it a bit more to be sure, but I think that in this case I've previously used a weld stress along the length of the HSS that has a linear profile from start to finish.

RE: "Stiffeners" at torsional connection

(OP)
BA: I would love to do that - 22.8k/(1.392*1/2") = 32.7" for a transversely loaded 1/2" fillet weld. If I lose the constraint on the footing dimension that would work well.

In Russia building design you!

RE: "Stiffeners" at torsional connection

(OP)
Never mind that: AWS indicates effective lengths for only end-loaded weld lines.

In Russia building design you!

RE: "Stiffeners" at torsional connection

a7x1984, are you sure you are reading that weld capacity correctly? In Canada, a 1/4" weld 6" long would have a factored shear value of 1.28*150mm = 192 kN or 43.2k. That is equivalent to an allowable shear of 28.8k. I doubt that your weld values are much different.

BA

RE: "Stiffeners" at torsional connection

Another possibility is to use a 4x4 angle welded to each side of the 5x5HSS with a couple of anchor bolts each. In that way, the base plate may be omitted entirely. If the bolts are spaced at [2.5+5+2.5] = 10" o/c, the tension per bolt is 9.5*12/10/2 = 5.7k, a light load for a 3/4" dia. A307 bolt.

BA

RE: "Stiffeners" at torsional connection

Quote (a7x1984)

BA: See attached pdf from AISC Manual. First page has longitudinal capacity, second page has 50% increase for transverse loading.

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

(OP)
I like that one too, BA.

In Russia building design you!

RE: "Stiffeners" at torsional connection

BAretired,
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

(OP)
Good lord. I need to go back to wood design.

In Russia building design you!

RE: "Stiffeners" at torsional connection

Quote (BA)

D is given as the number of sixteenths in the diameter, so 1/2" is 8 sixteenths.
should read:
D is given as the number of sixteenths in the weld size, so 1/2" is 8 sixteenths.

BA

RE: "Stiffeners" at torsional connection

Sorry, I am a slow typer, I see you have it figured out

RE: "Stiffeners" at torsional connection

Quote (wannabeSE)

BAretired,
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.

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

(OP)
Without the prequalified weld, I would rather go with BA's suggestion. Thanks, guys. At least we know my previously designed fillet welds aren't going anywhere.

In Russia building design you!

RE: "Stiffeners" at torsional connection

a7:
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

(OP)
dhengr: My point is that, as a service to the community, I am willing to spend more of my own personal time to shave off every dollar I can (i.e. explore various options and configurations). There isn't always a lot of additional time spelled out in the proposals for narrowing down to the dollar. When a community organization has a budget hinging on a few dollars, they need some extra help. That is what I see as the difference for me - nothing about sacrificing a sound design.

I am having a hard time visualizing your idea at this time in the night. I will try again in the a.m. =)

In Russia building design you!

RE: "Stiffeners" at torsional connection

I'm having trouble seeing this as being much of a problem. Because the plate is bolted, the end of the weld (nearest the extension of the HSS off of the pedestal) is may NOT be where the greatest weld stress is. It could be close to the bolts depending on plate thickness.

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 winky smile

http://www.eng-tips.com/supportus.cfm

RE: "Stiffeners" at torsional connection

(OP)
swearingen: It is a true force couple - no uplift. I agree with you on the anchor bolt comment; makes sense.

In Russia building design you!

RE: "Stiffeners" at torsional connection

If that's the case, then if the internal moment arm is about 9" (center of bolts closest to free end to end of HSS), then the tension on the bolts will be about 12.7k, or 6.4k per side. This is ignoring the other bolts, which do help. With this force, a small J-groove weld would easily hold it - no stiffeners and their requisite cutting, fitting and welding needed. You need to remember to design the plate thickness/bolts for prying action.

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 winky smile

http://www.eng-tips.com/supportus.cfm

RE: "Stiffeners" at torsional connection

(OP)
No prob: The HSS is about 6 ft long. There are two vertical HSS (about 6 ft tall) centered on the HSS beam about 2 ft apart. This framing supports large, plate-like permanent artwork (elephants in this case) that sandwich the vertical HSS's. The panels of the artwork are 16 sq.ft in surface area and made up marine-grade plywood. Not much dead load, but a lot of wind load on the panels.

In Russia building design you!

RE: "Stiffeners" at torsional connection

a7:
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

(OP)
dh:
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.

In Russia building design you!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources