Buckling of Anchor bolts 1

[magmath76]

During construction,I have come across to an event that the anchor bolts supporting the central column buckled during erection of an elevated tank. I would like to calculate if that buckling is within the acceptable limit. Any help would be much appreciated.

 

[hokie66]

A photo or two would help. What caused the distortion of the anchor bolts? Just vertical load or was there a lateral component? Was the distortion caused by buckling or perhaps bending? A description of the column base would help, with size and number of bolts, etc. Anchor bolts for a column are typically not subjected to gravity loading, so would not buckle. Was there no grout under the base plate?

If you want advice, try to give us as much information as you can.

 

[magmath76]

Hi Attached is the photo of the column with buckled anchor bolts.
Column is a circular pedestal with 50mm thick base plate x diameter around 1125mm
it got 28 off 30mm anchor bolts
No grout under the base plate, column was supported on leveling nuts
It is a thickener tank, it happened during hydrotest.

 

[JedClampett]

You got real problems. Those bolts have zero capacity. I don't have the definition of buckling in front of me, but I'm sure it says something about uncontrolled deformation without any additional load. Structurally, unlike yield cases, we stay far away from any loads where buckling controls for that reason. I would be interested in what caused this, especially since the largest loads occur when the tank filled with water, not during construction. Maybe the lack of concrete around the bolts removed their lateral bracing and they acted like a series of little columns. Their kl/r (r being very small) became large enough where the buckling load was exceeded.
You're going to have to break some bad news to this contractor. Either remove or shore up that center column and rebuild the base from scratch or at least enough to completely reinstall the bolts. And don't let them try to get away with heat bending the bolts.

 

[dhengr]

Those bolts appear to be standing, unsupported, in 6 or 8" of water. Also, why are the holes in the base plate slotted. There is another full sized hole to the right of (counter clockwise of) every bolt, what’s that all about? I doubt that that column was intended to be loaded without being fully grouted. That whole foundation situation looks screwed up. Is that what the construction drawings showed?

 

[hokie66]

Screwed up, indeed. A grout pocket without any grout. What were they hydrotesting? The tank I presume, but there were unintended consequences.

Why are there so many bolts, anyway? What is their purpose?

Are there any bolts which are fractured? If the bolts are mild steel, bent but not broken, they could perhaps serve whatever purpose intended, provided you can live with the deflection which has now been built into the tank. If not, perhaps using a grout filled flat jack to jack the tank back into position is the way to go.

 

[magmath76]

Bolts were incorrectly casted in the first place and for the alignment of the columns the holes had to be slotted. I do not see, by visual any fracture on the bolts and also checked with a "hammer sound". Surprisingly one bolt stand upright as it was without any any bent. Construction drawing shows the same thing but only 230mm of pocket depth but the actual measured depth is more than 300mm.

 

[LittleInch]

I suspect two things - 1) - some of the bolts were already "bent" to get them into the slotted holes and 2) Someone forgot to figure out what the tank weighed when full of water instead of partly full with it's normal contents.

I wouldn't accept this in any shape or form. Loading up columns like this without the supporting grout being inserted and allowed to go off is simply negligent behaviour by the contractor and he needs now to suffer the consequences.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[ztengguy]

Whats the purpose of having that many bolts? Is there major uplift or overturing that you need to provide them for? Do you have a picture of the rest of the tank so we can really see what the construction is.

Without all the background, its a reinstall by my book. Do it right, or dont do it at all.

 

[SAIL3]

At first glance, I would have to aggree with Littleinch....following the clues...bolts misalligned to begin with which would suggest an attempt to lign them up with the holes in the base pl.....if it was a case of buckling of the bolts then why did the buckling not progress to a more advanced stage and be more uniform around the perimiter, unless, only some of the bolts were bent initially to align up with the holes ....however, the unsupported length of these bolts looks dicey and untill one has the total tested load and unsupported length of the bolts one can not make an informed analysis....

 

[fegenbush]

I am going to agree with LittleInch's second paragraph. This is unacceptable in every way possible. Absolutely gross negligence to an extent I have not seen in quite a while.

Please correct this situation before someone gets hurt of killed. For the record, a correct solution to this problem does not involve calculation, but rather it involves cutting, welding, etc.

 

[TDIengineer]

Did the connection experience torsional loading when water pressure was applied? is there a bend in the pipe above that would throw massive torsion when pressurized?

I see twisting plus compression failure.

 

[msquared48]

T thought about torsion too, but the head of the bolts are at the opposite side of the slotted holes from what I would expect if that were the case. I suspect some alignment problem since all the bolts appear to be to the same side of the slotted holes in this picture, possibly being pried into the position by ... whomever... that bay have induced an eccentric column condition to the bolts.

Oh, and the number of bolts - was this designed as a flange connection to take hydrodynamic tension rather than compression?

Mike McCann
MMC Engineering

 

[hokie66]

Until magmath answers the question of why so many bolts were required, and what are their purpose, we don't even know if the bolts are necessary. I would probably be more concerned that those gas-axed holes have decreased the bending capacity of the flange.

 

[magmath76]

Bolts are for overturning moment caused by seismic and wind loads, which is estimated at 2600KNm. Attached is the photo of a full tank with its supporting arrangement. no bend in the pipe noted.

 

[hokie66]

The tank has extensive cross bracing at the exterior, so that is where the lateral loads will be taken. If the central support has to take 2600 kN-m, you have big problems. But I doubt that is the case. I think a new analysis is in order, to define the actual loading on that central column. Is the base plate continuous under the column, or is there an opening?

 

[fegenbush]

If the bolting is for pressure/piping as msquared48 mentioned, it may be possible that there is a mismatch in the flange types. This is a common problem with large diameter flanges as there is a difference between API/AWWA/ASME B16.47 Series B and ASME B16.47 Series A flanges. Some of the sizes have the same number of holes, but different bolt diameter and bolt circle diameter. That might lead a crew to try to bend the bolts to match the mating flange.

This does not change the fact that a repair is necessary.

 

[JLNJ]

Maybe this "column" saw vertical loads far beyond what was anticipated. Just looking at the photo, it seems like the forest of smaller columns should have born most of the load. Possibly a strain compatibility or foundation settlement issue?

 

[Ron]

I noticed the tank bottom sheets have deflected between the bents. There is no secondary support here.

Bolt displacement appears post loading as compared to pre-installation bending....no marks on the bolts indicative of mechanical bending and some are on the wrong side of the slot to have been done for that purpose.

This is a screwy design....why would the central column be loaded so heavily when you have a substantial structure otherwise? Granted, all of the interior columns would be loaded heavier than the exterior ones; however, that could be easily handled without passing high loads to the central column. Is there a discontinuity between the end of the bents and the central column? If so, you have a whacky load path.

Is there a chance that the central column was intended for mechanical purposes and not structural? Seems not with so many bolts, but I suppose it could be. Maybe the bolts were only sized to take the self weight of the column and maybe a small amount of sheet/liquid above and it is taking more than anticipated because of the screwy load path.

If foundations for the first row of supplementary columns settled, it would put more load on the central column.

No answers, just more questions.

 

[magmath76]

Base Plate is a solid 50mm thick plate with no opening and it got a shear key as per the attached.