×
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 in Large HSS Columns

Stiffeners in Large HSS Columns

Stiffeners in Large HSS Columns

(OP)
I have a custom HSS section that is approximately 5' x 10", it is being used to support large overhead doors.

My question is, the section needs to be stiffened at the top where the pulley assembly mounts to the column. How do I determine how far the stiffeners should run below the mounting bracket.

I'm worried about creating a point where the stiffness changes drastically and creates a "soft spot" in the column.
The load the stiffeners are holding is about 1/8 of the wind load (Which acts in the strong direction of the column and opposite to the dead load of the door).
So if the stiffeners run to far down the column I would have the same problem from the wind force which is much greater.

any input would be greatly appreciated.

RE: Stiffeners in Large HSS Columns

A sketch might help.

BA

RE: Stiffeners in Large HSS Columns

5 foot x 10 inches is a mistype, right?

This sounds like a basic stiffened seat design from the AISC manual but I'll reserve judgment until we get some more info.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Stiffeners in Large HSS Columns

(OP)
Please see attached sketch.

The initial wasn't a mistake, the modifications are required to an existing section as the pulleys and sheaves being mounted are changing location.

Also I am working with the Canadian steel code, if the AISC covers the topic better I would greatly appreciate some input in a direction to look.

Thanks

RE: Stiffeners in Large HSS Columns

Ok, that's cool. And nothing like I imagined. I see your bracket dumping moment directly into the stiffener behind it. That stiffener will need to be sized for flexure and shear etc. The stiffener will then dump the moment as a vertical force couple in the walls of the column. Size the welds accordingly.

Are you using the stiffeners to bring down the b/t ratio on the wide face of the column? If so, they'd need to run the full length of the column.

The localized stiffening doesn't bother me any.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Stiffeners in Large HSS Columns

(OP)
No the stiffeners are not needed to reduce the b/t ratio. the column as a whole can withstand the loading. I was more worried about having some type of local buckling where the stiffener ends.

RE: Stiffeners in Large HSS Columns

I see your point. You'd probably have to turn to Roark's to evaluate that. Fundamentally, it's not that different from the single plate shear tab connection that we do all the time without checking for buckling under the tab.

Out of curiosity, how are you dealing with the b/t issue? I've got that at 152 for the wide face. S16 table 4-2 limits you something around 38 depending on your steel grade. I did something similar for a free standing canopy once. We had to weld angle stiffeners to the inside of the wide faces to keep b/t from getting out of hand. Maybe since the column is existing, it's already stiffened.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Stiffeners in Large HSS Columns

I'd make the bottom edge of the stiffener on a 45 deg angle.

Faith is taking the first step even when you can't see the whole staircase. -MLK

RE: Stiffeners in Large HSS Columns

I'm curious too. How can such a large b/t ratio be justified by S16?

BA

RE: Stiffeners in Large HSS Columns

(OP)
S16 Table 4-2 (Look to take Table 2, pg 1-127) which given more limits.
basically if your b/t ratio is larger then the limits provided then you have either have a class 3 or 4 section. So for a Beam-Column analysis you can turn the section into an equivalent size that fits within the limit.

So take the b/t ratio, back solve for "b" then calculate your section strength with this property, realizing that that portion of the section is only able to fully develop without localized failures.

so specifically for the calculation that 5' long wall in theory became something like 1'-4".

RE: Stiffeners in Large HSS Columns

not knowing the thickeness or the actual loads...vital info. However, it looks like the only effective portion of the col for axial loads are the two end segments which would give you two vertical channel-shaped sections. There is no effective stiffening for the brkt & stiffener located @ the brkt.I would add horiz stiffeners at the top of col and at the bottom of the vert stiffeners. What this leaves you with is a quasi-horizontal bm in the top portion of the col eventually supported by the two effective vertical channel portions at the ends. If you did not have an applied mom at the brkt and just dealing with vert loads, then the center portion of the 5ft length can still transfer in shear this vert load to the end sections even though this portion does not have an axial load capacity of any useable magnitude and as a result would not need that quasi-horiz bm at the top.

RE: Stiffeners in Large HSS Columns

I think that the best way to deal with this is to use an effective Fy that satisfies b/t rather than an effective section. In your case, Fy would about 7 ksi assuming the real Fy is 36 ksi. In theory, this would obviate the need to follow Sail's recommendations. I'd be tempted to follow Sail's recommendations anyhow though as they just sound like thoughtful detailing to me. This is a good situation for belt & suspenders thinking.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Stiffeners in Large HSS Columns

Correction: I think you'll need to scale to SQRT(Fy). I'll double check when I get back to the office.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Stiffeners in Large HSS Columns

If we are using Table 2, a Class 3 section permits b/t to be 670/√Fy, so for b/t = 160, Fy = (670/160)2 = 17.5 MPa or about 2540 psi.

Welding continuous stiffener plates inside an existing hollow section is not possible, but it may be possible to attach the two five foot wide plates together at discrete points from the exterior in order to provide some stiffening.

BA

RE: Stiffeners in Large HSS Columns

Thanks for doing the math BA. 17.5 MPa is pretty lousy. Aaron's proposal may produce more advantageous results.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Stiffeners in Large HSS Columns

as BA pointed out welding inside the HSS may be difficult.
I would ,if possible, close off the top of the col with a flat pl and put cutouts in it if reg'd. For the bottom fla of the quasi-top bm I would add a horiz external stiff if it is not possible to add one on the inside. With a top bm of depth up to 10" , it may be possible to get a weld rod in the...10x10" opening clearance.
Rather than do all that fab, the other possibility is to weld a ,say HSS10x10 to the top of the col , close off the ends with a pl that extends dn the ends of the col a certain length or extend the ends of the col up to use as a closure pl for the HSS10x10. Then detail a brkt conn to this top bm. I always try to close off the ends of HSS members...open ends on HSS members , not good. Ofcourse, none of this may be applicable as the info supplied is not complete.

RE: Stiffeners in Large HSS Columns

If there is access from above, could insert a full height C9x13.4, in line with the eccentric pulley load. The C9 could be welded front and back from the top as far as the welder can reach, then spot welded to each 60" x 3/8" plate periodically through pre-drilled holes in each plate.

BA

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