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!

 

[EngineeringEric]

Can you fill the column with fine grout to a height above the dent? Keep it from local buckling inwards?

I did a similar repair as you mention with a round tube (10"OD): I added studs, i wrapped it with a 18"(?) pipe halves-welded, i filled it with concrete. I designed my studs to transfer the vertical load of the column into the concrete above the dent and 'around' the dent.

Edit:
Also, suggest painting more of the column and possible bollards to keep the forklift driver from hitting the repair... maybe dangle a tennis ball from the ceiling?

 

[Guastavino]

EE,

Thanks much, and I can fill the column. They also want the protection, so I'm thinking just form up around it and place concrete, or a steel pipe welded would be great too if they want to spend the $.

I feel bad for the next forklift driver...

Interestingly enough also, they asked me for a "repair" option and "protect" option. I can't see a simpler repair than forming it with concrete since they want it protected too. Only other option I see with steel is for them to temporary shore, cut out the bad piece, put in a new piece and full pen weld it. And even then, I don't know how you get backing bars in there to do that and I think you would need them per AWS wouldn't you?

 

[KootK]

You could also do something like this for the lower 4' combined with one of those guards that was mentioned in my thread. It avoids SOG work and can be numerically verified with relative ease.

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]

I like EngineeringEric's solution for this one.

 

[msquared48]

Used it before and it works great. I agree with EE too.

Mike McCann, PE, SE (WA)

 

[EngineeringEric]

My new favorite thread of all time!

I think that the steel sleeve will add more protection from impact than just concrete surface, the concrete will get chipped and hammered by forks, the steel sleeve filled with concrete will ding, scrape, but will only fail when it shears off the entire system...

Have fun!

 

[KootK]

I feel that, as with most engineering decisions, the correct answer is the lowest cost answer that is sufficient (as opposed to excellent). While I very much like the finished product that would result from the armored elephant's foot scheme, I think that the butcher's bill is just too high for something that probably doesn't even require repair in the first place.

If you presented the client with a concrete reinforcement scheme and a steel reinforcement scheme for them to price, I have a tough time seeing them choosing the concrete option unless they'd been biased towards protecting the snot out of the thing. Consider the work required for both schemes:

Concrete Reinforcement

1) Mobilize a stud welding machine to come out and do just a handful of studs.
2) Order a large, uncommon steel tube segment and have it cut in two in the shop.
3) Demo the slab on grade if OP decides to implement that.
4) Perform a vertical orientation full/partial groove fiel weld of the tube halves.
5) Cast non-shrink concrete around the outside of the column.
6) Drill a hole in the column and fill it with non-shrink grout.
7) Weld a patch over the grout hole if you're inclined to do so.

Steel Reinforcement

1) Order of few length of some common material that will be lying around any local shop.
2) Fillet weld everything in place.
3) Wait for your fence thingy to show up in the mail.

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,

Great points. So my concern with your channel detail are:

1. I think the tube column is already too bent out of shape. There isn't a straight side to put in the flat plate. It's bulging both sides.
2. I don't want to bear the channels on the concrete below in order to transfer that load. the damage extends low on at least one of the two affected columns. so I might not be able to develop the plate on either side.

With that said I like your detail and am open to other suggestions.

Also, one other question in terms of HSS shape splices (can't work hear because of constructability), but don't you have to have backing bars if you did a full-pen weld?

 

[hokie66]

Yes, you need backing bars, but they will be placed in the shop.

The steel sleeve is dead easy and simple, and I don't even believe the studs are required. The steel provides excellent restraint for any bursting stress. And the impact resistance will be much superior to either just concrete or steel shapes.

 

[Guastavino]

Hokie,

Thanks. Problem with full-pen welds and backing here is that you can't put a new piece if there are backing bars in the way because it wouldn't fit on the existing column. Unless I'm missing something?

 

[hokie66]

I don't understand your problem. The backing bars go on the half circles, either one on each piece or both on one piece. The bars would only be say 3 mm thick, so won't really take any additional space.

 

[KootK]

Hokie's talking about welding the outer, amoring tube; Nick's talking about welding a replacement chuck of the original column into place.

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.

 

[KootK]

1. I think the tube column is already too bent out of shape. There isn't a straight side to put in the flat plate. It's bulging both sides.

Bah! I set my original detail up assuming that the flexibility of the the flat plates would allow you to "hug the curve" as it were. The sketch below shows how you might handle it in a more extreme case. If you can find 4" of decent column above or below the damage, you should be good to go.

I don't want to bear the channels on the concrete below in order to transfer that load. the damage extends low on at least one of the two affected columns. so I might not be able to develop the plate on either side.

No, certainly not. Again, you only need a small amount of healthy column at the bottom to get the job done. How about a pic of the column with the lower damage?

and I don't even believe the studs are required.

I question this. Baring a vary long sleeve, without the studs I would expect the compression to remain in the steel section. And I wouldn't trust internal grouting to prevent further HSS wall buckling given:

1) How the extreme dents would push into the grout.
2) That grout shrinkage would probably crack the grout right behind the dent.
3) That the grout above the dent could be forced upwards.

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,

I really like both of your details, so I'm going to give both options. KookK, after further inspection, I think your first idea can work. And, if it can't based on field dimensions, surely the 2nd detail can. What do you guys think of the below? I'm thinking I don't need to had rebar to the concrete filled section because it's already confined, but I'm open to ideas.

As for the other detail, by my calcs, on a 40' column I need about 71kips of ASD load. The controlling welds are the vertical flare bevels which I calc at 70ksi*0.6*(2*3/16*5/16 eff throat)*8"long*4total welds/2(omega)=78.75k capacity of weld. The fillets on the 1/2" plate and c15 are a slam dunk.

Only other thing with KookK option. what do you think about the moment capacity being compromised and impacted the KL/r ratio above, etc. I'm not really sweating this in this instance, but curious how a somewhat weak link might impact.

Disclaimer to any future users of this detail, it's not Finished, preliminary!

 

[jreit]

njlutzwe, would you need any reinforcement to transfer loads from the concrete in the 20" OD pipe to the SOG?

 

[Guastavino]

jreit, good question. GOal of the detail is to transfer the HSS10x10 load to the studs above the damage to the concrete and then back into the studs below the damage back into the original column.

Now, in the real world, it will likely go into the diamond cutout of the slab that bears on the footing below, but there is a load path other than that. Does that make sense?

 

[KootK]

Sexy details! Comments:

1) I my original detail, I'd intended the flat plates to go the full height of the repair which would address the kL/r issue. Because the damage is so low in the column, however, it's probably not important here.

2) I'd hold the steel up 1/2" from the SOG.

3) Why's the steel repair so tall? Seems like it could be about 2' long centered on the damage.

4) I worry a bit about vertically restrained shrinkage craching in the concrete. Perhaps bond with the inner and outer tubes us enough to deal with that. I'd be tempted to specify a low shrinkage mix.

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]

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.

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?

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.

The way i view the column-repair, maybe likely in error, the column is holding itself up now (maybe no safety factor?). I want to support the damaged area so it does not deform under new loads, i want to take any new load, and i want to restore some of the surplus capacity (safety factor). What ever accomplishes that great. Concrete takes load, keeps it from moving downward (if it cannot move down it cannot buckle inward), and if i make a big enough ring/box i don't care if the column i out of plane by 2" vs 2.5". I have reinforced dents with big L angle columns welded on the sides of the column beyond the dent to keep the column from deflecting down... it worked well and your detail is similar but with more welding (required for degree of damage)

 

[EngineeringEric]

Lovely details, and my post took too long to post.

I would maybe add some studs in the middle of the column, including the damaged area to help keep that area from moving inward (yes tension of concrete)

I'd specify non-shrink non-expansive fine grout for the concrete.
Maybe slope the concrete at the top to keep people from spilling their sodas on the concrete flat surface

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