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Damaged Large Pipe Column Repair

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azcats

azcats

Structural
Oct 17, 1999
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I've got a large pipe column supporting a sign structure that was hit by a large vehicle (Semi Tractor) and damaged. Pipe is 36" dia x 0.375" wall thickness. Photos linked below.

The column is cantilevered from a block foundation using lateral bearing to resist lateral loads. Axial loads are minimal relative to bending. My first instinct was to provide a wrap/doubler plate over the damaged area. The 'dent' is pretty well aligned with the sign face so that it's in the area of maximum bending stress. I'm in the midst of figuring out how to get the stresses transferred into and back out of the plate. But before I get too deep with that, I was wondering if any of you might have any bright ideas for repair that I'm missing. Or issues I'm not considering with this approach.

I'm thinking that I'll need to extend the wrap above and below the damaged area enough that I can provide a series of plug/slot welds to achieve the required stress transfer. I'm not really comfortable with a big fillet weld across the top and bottom and brief numbers show the sizing wouldn't be practical anyway.

One of my concerns is that the section isn't simply dented, but overly deformed where a nicely rolled plate wouldn't fit over the dented area. I wonder if a series of adjacent channels spanning the dent would be more practical. At least with those the flanges could be trimmed to fit over any deformations...and then I could use all fillet welds. Hmmmm...

Foundation damage is going to require the removal and replacement of some concrete below grade.



Thoughts are appreciated.
 
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My first thought is to use vertical plates, not channels. The inside edge of the plates would be cut to exactly match the contour of the dent. The outside edge would be vertical. The outer shell could be made in three or four sections which would meet and be welded to the vertical plates.

The new shell could be curved to the appropriate radius and would act in conjunction with the vertical plates and dented shell for a strong composite section.

BA
 
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Consider cutting the damaged area out and butt-welding a section (or maybe 2 sections) back in to replace it. Weld a couple of beams on for temporary support.


 
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I'd check the capacity with a concrete filled section. That would not repair the damage done already, but would reinforce against further buckling. The normalcalacity increase just by doing this is somewhere in the order ot 30%.

You still might be able to weld a curved plate to the outside after that, and/or frp wrap as mentioned too.

Mike McCann
MMC Engineering
 
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My first thought, and it would take some examination before I could go with it, was to nibble/shape some vertical plates to be welded perpendicular to the pipe. These would add section and be an active restraint against further buckling.

Michael.
Timing has a lot to do with the outcome of a rain dance.
 
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The column needs to be "rounded back to round" - "straightened back to round" ? - the language is difficult to write right. 8<)

Difficult to do. You need to "push in" at the points where the column is "bulged out" from nominal, and (somehow simultaneously) "pull-out" where the steel is bulged in from nominal. The steel now is "popped" inside nominal across one part of the arc, and bulged out at both ends of that arc. Once it is "rounded" inside nominal all the way across the dented area, then you can weld a new rounded (rolled) plate over the "bulged in" areas.

I don't think a chainfall wrapped around the column - no matter how cleverly applied - will work unless you can "focus" the net pressure on the specific area bulging, without further kinking the good parts..

What material? Painted carbon steel or aluminum? Galvanized?
Can you get into the inside of the column - even if that might be difficult?

I've got some ideas, but they might be unorthodox.
 
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@racookpe1978, The writing may be difficult, but your fix is impossible. The process you describe will not achieve the objective, there is no process except cutting out and replacing the damage that will work.

Michael.
Timing has a lot to do with the outcome of a rain dance.
 
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Oh, I agree completely with that requirement to "replace the structure" ..

But, if the existing steel can be bent back into a shape where a properly rolled cover plate can be fitted over the dent, then welded all-around to the existing column, then you would not have to remove the dent. Its strength is replaced with the good plate now carrying the load.

my question was finding ways to straighten the column where "dented out" so as to allow the replacement cover plate to be fitted around the column. Hence, my question about material and my question about access into the center of the column. Both are intended to find ways of "moving" the crimped (popped out) corners of the dent.

As-is, if you can't straighten that dent, then you must cut out the bad steel and weld on the replacement cover plate - but carry the load for the sign while the guts of the sign's column are cut out and being welded.
 
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Thanks for all the input and suggestions.

It is a steel pipe with no current or simple access inside. And at 36" dia, I'm not sure how practical it would be to work inside. The sign is in a rural area so I don't believe attempting a repair that's not a sure thing is a good idea.

The top of the structure could be fairly easily removed (bolts) if we decide to go with the removal (of the damaged section) and replacement route. But expense on that might be excessive with CJP welding and required inspection/testing. Plus a more significant crane that might not otherwise be needed.

Any thoughts on using T sections and nibbling/shaping the web to match the contour of the damage? Could weld stiffeners between the pipe/web/flange if required for flange bracing. Sort of a hybrid approach of BA's and ra's ideas.

Thanks again.
 
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I would look at encasing the section in concrete, with vertical bars to resist the flexure, ties for confinement, etc. Extend the encasement high enough to ensure transfer of forces between the pipe and the concrete. If needed, weld studs or vertical "fins" to the pipe to help transfer forces.

If buckling of the pipe is a concern, drill holes thru the wall and pump in self-consolidating concrete to above the height of the damage.

Check the footing for the added weight of the concrete... if overturning moment controlled the size of the footing, the added dead load may not be an issue.

Good luck,

Brandon Rossetti
Rossetti Engineering, PLLC

 
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If you were to build a submarine out of that tube, you couldn't take it down very far.
E.g. collapse pressure would not exceed 78 psid for a perfect tube, and 51 psi for one that was out of round by 10mm, assuming syp=36ksi and some other stuff.

I know it's not externally pressurized, but consider the possibility of pressurizing the interior in an attempt to de-dent the tube, at least partially. The sign may be tall enough that just filling the tube with water might be sufficient.



Mike Halloran
Pembroke Pines, FL, USA
 
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The load would have to be take off the 36" pipe column during this operation, but otherwise, find someone who is very good with a rosebud heating torch, and has experience heat straightening and bending steel. This will be a tougher job (maybe not practical) since he can only heat from one side. Cut vertical kerfs every 6 or 8" up through the bulged or dented region; this makes the process easier since it turns each plate element into a more plane plate element rather than a three dimensional shape. The kerfs get beveled and welded back up after straightening. Then a new rolled cover plate gets added with some regular plug welds to the straightened steel pipe, plus a fillet all around. Disadvantage..., the mating surfaces might be more susceptible to rusting, maybe a few drain holes left in the lowest fillet weld regions would fix this.

I also like the idea of filling the pipe with concrete to an elevation above the damage. Then, also cast a 6 or 8" thick concrete skirt all around the outside of the pipe, with a top sloped to drain. Tool a reglet all round the stl. pipe to be filled with caulking. Reinforce the skirt with vert. bars and with hoops just as you would a round conc. column.
 
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Weld a 6"x6" steel ring around the column above and below the damaged area. Leave the damaged pipe as is. Fit hefty steel verticals between the two rings and weld wherever possible. Place two half cylinders with radius 24" on the outside of the verticals and weld in place. Make'em good and thick. Maybe cover them with rubber bumber material as well.

This will provide a four foot diameter pipe in the lower six or eight feet but who cares? Beauty is in the eye of the beholder and this would provide a solid resistance, a sort of bollard, to the next yahoo who drives into it.

BA
 
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alot of good ideas presented....here is a slight variation on BA's....full ring top & bott say 24" away from damaged area...vert memb each side of dent say 12" beyond damaged area...then run vertical members in between as req'd from top ring to bottom ring...could be T-sections or other aesthetically pleasing cross-sections.....leave the dent in-place...check that there is enough length left below the dent to transfer the loads from the reinforcement back into the column shell and if not enough length , extent vert members to fdn and address the transfer of load in them to the fdn.....also check for overall plumbness of column...also as dhengr mentioned those experienced in heat straightening can accomplish amazing results....
 
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See attached sketch for an idea that expands on what the others have recommended.

The strength member - the replacement steel - would first be rolled as a 36 inch diameter inside dia. Thickness would would 1/8 thick (or 1/4 inch) thicker than the current column steel. This would let a complete fillet weld be established all the way around the added belt.

Belt needs to be long enough to extend at least 3 to 6 inches longer than the dented area is tall.

belt should not be a complete circle, but, after rolling into a circle (or half circle) should be cut into 6 sextent parts. Leave approximately 1-1/2 to 2 inches between each segment for two vertical welds. A fillet weld around each segment provides vertical as well as horizontal support, and is easier to handle in the field and weld and build than a series of slot welds. The segments will cover up the 3x handholds.

the two handholds that cut out the kinks will allow the dent to move under the pressure of the internal threaded rod or hydraulic jack. Excess rolled steel plates inserted as stiffeners between the jack and column will prevent the threaded rod (or jack) from deforming the column steel at each end.
 
 http://files.engineering.com/getfile.aspx?folder=2b2a323f-d5bd-4ce1-ae30-bad782172987&file=36_Pipe_Column_IMG_3121.jpg
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In more detail: Divide the damaged area in half vertically. Fillet weld a stiffener beam on one side close to the divider line. Cut out the other side of the damaged area, tack back=up bars on the inside, fit a new piece of pipe in & butt-weld. Weld a stiffener beam over that side, gouge the beam off the first side, insert a similar piece there, then weld the seam down the middle.

Contact people that actually do this kind of work, and they can give you a good idea of what's practical for them.
 
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