Buckling of Anchor bolts
Buckling of Anchor bolts
(OP)
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.






RE: Buckling of Anchor bolts
If you want advice, try to give us as much information as you can.
RE: Buckling of 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.
RE: Buckling of Anchor bolts
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.
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
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.
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
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
RE: Buckling of Anchor bolts
Without all the background, its a reinstall by my book. Do it right, or dont do it at all.
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
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.
RE: Buckling of Anchor bolts
I see twisting plus compression failure.
RE: Buckling of Anchor 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
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
This does not change the fact that a repair is necessary.
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
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.
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
Magmath, once upon a time, I got involved on some projects similar to this. We "inherited" a design method, and that method consisted of designing the radial beams for all the vertical loads involved and basically neglecting all other loads. When I began looking at it in more detail, it presented some real problems. Specifically, the scallop plates develop membrane tension, and much of that tension results in a large vertical load, for which the beams are designed. But there is also a net inward load on each beam from that tension, and if you start trying to find the leg loads, that inward component also produces a large moment that affects distribution of the loads on the legs, and shifts loading more to the inner legs. That kind of thing may or may not be part of the problem here, just be aware that the load at the center may have been miscalculated due to unwarranted simplifications in the design. An additional issue is that some amount of load from the scallop plates must be transferred to the shell, but you don't know how much. An additional issue is that if the scallop plates are detailed as cylindrical sections, you get sort of an indeterminate shape out of them in the assembled structure.
Where I ran into this, was we had circular ringwalls under those legs, and were getting differential settlement of one ring relative to the others- with the effect that when the tank was unloaded, it would pop anchor bolts out of the concrete on the inner legs, and base plates would be suspended a couple of inches above the concrete.
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
RE: Buckling of Anchor bolts
I am also wondering why the center column should be designed to attract so much lateral load. It is unlikely that the connection between the radial beams and the center column can generate the kind of moment for the lateral resistance that is anticipated by the shear key and anchor rods. In an indeterminant structure like this I guess it is not surprising that center column bolts appear to have failed due to some unexpected lateral translation and racking under compression.
Ideally the lateral load should be taken care of with diagonal braces in the column array. The center column would then be modeled for bearing only with perhaps a horizontal slider connection to avoid attracting lateral load. A pinned connection could work if the center column is tied into the diagonal brace system.
Just a knee-jerk response based on two photographs :) Sorry to be a debbie downer. Maybe the design is fine and they just should have grouted the anchor rods before loading.
RE: Buckling of Anchor bolts
The bolts as shown are not adequate for any reasonable level of tension.
RE: Buckling of Anchor bolts