HSS10x10 Column Dents 1

[Guastavino]

Hi All,

KookK had a great thread last year about column dents, and I've run into a similar issue, but I'm thinking this one merits some repair. See below pics.

It's a 40' tall HSS10x10x3/16 in 50' square bays with a TPO roof, ie very light. The bottom 4' are what you see. Column appears plumb as I put a level on all sides.

Here are my repair thoughts, weld 3/4"x4" studs at 12" o/c on each side and encase it with concrete, either 2' diameter or 2'x2' square pier that has stirrups and vertical bars that are epoxy anchored into the "pier", ie concrete to fill slab cut out, below. My thoughts are that that will stabilize any buckling opportunity and transfer load as required.

Problem is, I don't feel like I can "design" check this. It's just judgement based that load can transfer to the studs around the bent areas and then back into the column at other studs and it will stabilize buckling etc.

What blinds spots do I have?

Thanks to all!

 

[KootK]

With your detail, would you see any problems with welding perpendicular to the face of the HSS Wall on the only walls that are probably supporting 100% of the axial load; similar to transverse to a flange of a W-Beam in highly loaded condition? And then 4-times.

It's certainly worth of consideration:

1) In my original detail, and the one that I recommend if it's possible, there would have been full height flat plates and no transverse welding.

2) It's somewhat of a different situation than with a wide flange beam.

2a) Your axial stresses in such a slender column should be no where near those in a beam flange.
2b) You've got four sides sharing the load. You can rotate the welding with some cool down time in between.
2c) Softening a beam flange can lead to flexural deflection in the beam under load. Less of an issue in a column.

3) Now that I think of it, one could do parallel welding with the stitch plate option as well. And that would be an improvement.

I don't even think that a PJP weld is 100% necessary. One doesn't need 100% of the compressive strength of a composite steel section, a simple chamfered edge and fillet-groove or something should be more than sufficient for a sleeve... or am i missing something?

If the look would be acceptable, you could just fillet weld on a radiused splice plate.

Concrete just allows for more construction tolerance and unless you have a highly detailed 3d measured deflected column then you run the risk of things being skewed.

Non-issue. It's just fine if things are skewed.

KootK's, Should you cap this thing with something? keep the top closed off?

Maybe for aesthetics but certainly not for structural purposes. There's no doubt that the concrete solution is prettier and cleaner when all is said and done. My only beef with it is the cost.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Guastavino]

KookK and EE,

1. The reason I opted out of Parallel fillet welds as opposed to flarebevel at the corners is because the bottom plate has to be so close to the bottom that I didn't think it would be constructible to put a fillet weld that close to the floor.

2. Reason for the height is that some of the damage extends to nearly 4' on one of the columns. Not sure I posted that picture.

3. I think I'll show a vertical rebar in between each pair of studs to accommodate shrinkage based on 0.0018*area. As well as spec non-shrinking grout fill.

4. I might add a layer of studs at the damaged area too just to "hold" it in place. Belt and suspender approach.

5. I get the concept of holding it 1/2" off the concrete, but my thought is that if I leave it flush, it's just one more load path in the case of emergency. Theoretically I get the not wanting to load the slab infill, but if this column were to ever experience an overload, it would at least have somewhere to go, albeit "junky" fill-in concrete. Are there other downsides im not thinking of?

 

[KootK]

My 1/2" gap suggestion was only for the steel option. I would also leave it flush for the concrete.

In your steel detail, I would make mention of the fence thing as part of your recommendation. From an industrial engineering perspective, I'd think that you'd want something in place to keep folks from bumping into the sharp corners with their bodies, not just their forklifts.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

you know what would keep people from bumping and stubbing toes or tripping and lawsuits... encase it in a round concrete shape

 

[KootK]

Absolutely. I've always thought that to be a nice feature of the concrete option. I'm sensing that your emotional investment in the concrete solution is rather high. Never fall in love with your own designs. They're the ficklest of mistresses.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

I actually like the steel option, it has real load paths not black magic concrete loads. I just thought it was a worthwhile poke. The ficklest is the most fun, would it fun if there was only one option?

I appreciate the back and forth as always! Have a good weekend (if those exist for you)

 

[KootK]

I'd be curious to know the relationships at play here. If I was the building owner concerned with resale value and the repair was being paid for by a tenant, I'd definitely go with the concrete option. If I was the owner of the building as well as the occupier of the space, I might go with whatever was cheapest. Age of the building and expectations for future use might factor in too.

It would be bold but I'm pretty sure that you could do a sonotube concrete wrap with a column cage and everything would be just fine. No casing, no studs. I've seen some composite column stuff and driven pile / pile cap research that leads me to believe that you cold fully develop the tube into the concrete in about 15" of embedment, even without the studs.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Guastavino]

So owner requested details to repair column for a tenant leasing the space. Not sure what option they will take. I'm going to give them both. They will price them with a contractor and pick accordingly. If they tell me which route they take, i'll try to remember to post an update. Thanks for everyone's help!

 

[hokie66]

I hate the one on the left. Just ugly and will need repair again soon, from experience in heavy industrial facilities, smelters and the like.

The one on the right grabs me. I would make sure those welds on the half pipe are complete penetration by using backer bars. The pipe is there to restrain the core, not carry the vertical load.

 

[KootK]

You hate the steel detail? Now that's some emotional investment. Has rapt hacked into your eng-tips account or something? I feel bad for my poor little steel detail. Inspiring such vitriol.

Just ugly

I was assuming this to be an industrial facility not the elevator lobby at Louis Vuitton.

and will need repair again soon

Based on anything other than this vague experience stuff? At the end of the day, it's just steel like the column itself. An integral part of the detail is, of course, the protection fence that has been mentioned several times.

I'd argue that the fence actually provides better protection than the concrete encasement. Every time that a forklift runs into the concrete, you've got potential for more steel damage immediately above and below the concrete. And now that the obstacle is twice as big as the original column, you're likely to have that many more impacts, each tending to batter the anchor bolts etc.

I would make sure those welds on the half pipe are complete penetration by using backer bars. The pipe is there to restrain the core, not carry the vertical load.

How much restraint could this lightly compressed concrete core possibly need? It's not as though it's the plastic hinge at the bottom of a moment frame or anything. By Nick's numbers I get about 3 MPa factored on the concrete section. I'd be happy to flange bolt the two halves together if that would't just result in more sharp edges.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Guastavino]

@hokie,

It's industrial space, so I don't care too much if it's ugly. And, they are going to bollard around it or put in some other bumper system to protect it. But if it happens again, they can fix it as such as time as that.

Agree on the CJP weld for the half pipe. Ultimately, they both work structurally, but as KookK brought up, one is just significantly cheaper than the other. I would prefer a slate roof for my house, but the asphalt shingles still work.

 

[hokie66]

KootK,

I'll only respond to the "vague experience" bit. It amounts to about 30 years, from aluminium smelters and reclamation plants, coal preparation plants, etc. I tried to tone down my language. Hate could have been "despise", and ugly could have been "horrendous". No emotional involvement here.

 

[KootK]

It amounts to about 30 years

The thing with experience, though, is that it actually has to be relevant in a statistical sense. Was it:

1) 30 years of using sexy concrete encasement details and having no problems OR;

2) 30 years of using horrendous details like mine and having lots of problems?

Only #2 would be statistically meaningful.

I've got this one residential contractor that I work with who had one 4" garage slab on grade settle and crack on him back in the 90's. As far as I can tell, nobody knows just why. For the subsequent 80+ projects, he's forced all of his structural consultants to place one lone screw pile in the middle of all his garage slabs on grade. No thickenings, no grade beams, still 4" SOG. There aren't even studs on the screw piles.

I tried to talk him out of this practice recently on the basis that, in punching shear, the screw pile probably couldn't carry a twentieth of the slab on grade tributary weight for some of these larger garages. He just won't have it. "Experience" has taught him, with absolute certainty, that placing a 4" diameter screw pile in the center of a three car, 4" SOG garage is the silver bullet for avoiding settlement problems. Sub-grade prep and the like are just esoteric concerns.

Experience with what works and experience with what doesn't aren't always the same thing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Guastavino]

I'll say this. My client likes the detail. And, it was a first time client. So I might get more work out of it.

All I could think of on my own that would work was a concrete encasement detail, but they specifically asked for a steel one as well. I was telling them I didn't think that a steel one would work without being a major operation. KookK's idea changed that, and for that I say thanks KookK!

@hokie, I'm extending benefit of the doubt that you're doing some friendly trolling to stir the pot. If not, I value your input, but I won't always agree with it, and for me that's ok. Fact is, I've never found an engineer I always agree with, and that's a good thing. At first I didn't like KookKs detail for this application because I didn't think it would work. Then I started drawing it and i realized it would work, and work very well.

Lastly, beauty is in the eye of the beholder, and my client wanted a cost effective solution option. So is it the best detail ever? No, but does it work and keep cost down? You bet, which is why my client likes it.

 

[hokie66]

Fair enough, njlutzwe.

KootK, I'll hold my tongue.

 

[KootK]

This is great. Now, whenever this comes up, we'll have two good, markedly different, canned details ready to go along with an exhaustive pros & cons list. If there's one thing that I know clients love, it's options.

KootK, I'll hold my tongue.

!@$#$%^!! You're getting too good at handling me. Might be time for a handle change.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Back to this one more time for me. In addition to strength and cost, perception is often an important consideration. For many people looking at the welded steel repair, whether they are engineers or not, I think opinions would be that the column has not been repaired, but rather just protected.