mcerd1
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| posted on 3/2/09 at 10:21 AM |
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OT - bent bolts ?
I've got a wee problem at work
a customer has managed to bent one of the anchor bolts that holds up a steel structure - its a very slight bend
the bolts are cast into the concrete and can't be changed without removing the whole foundation
I know that the bolt will still be strong enough (its an M24 8.8 FFS), but they want something to prove its still strong enough 
anyone know where I can find some theory on this to keep them happy ?
-Robert
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yellow melos
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| posted on 3/2/09 at 10:24 AM |
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Surely if it was able to get bent in the first place it has been used beyond it's design limits ??
or did sombody do somthing stupid to it.... like swing a 20 ton RSJ into it.
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BenB
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| posted on 3/2/09 at 10:26 AM |
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If it ain't fallen down yet it's strong enough 
I very much doubt there's going to be theory on "slightly bent bolts" on the basis that any effect on the bolt will surely depend on
how the bolt got bent in the first place, the loads applied to it etc etc.
Also 8.8 graded bolts will be tested to 8.8 standards. I'm pretty sure that test won't include "how much strength is left after
it's been bent a bit"....
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Steve P
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| posted on 3/2/09 at 10:28 AM |
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Is it still holding the structure? its strong enough then.
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nick205
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| posted on 3/2/09 at 10:34 AM |
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Can you still fit the nut onto the thread?
Can you "persuade" it back into shape?
Can you install another fixing/anchor point close by?
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gazza285
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| posted on 3/2/09 at 10:39 AM |
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Once the structure is built the anchor bolts have nothing to do but keep the leg plumb, it's not under any more load than how tight you have
tightened it. Tell them that you will have to employ the services of an engineer to calculate the new load capacity (which will not have changed,
steel is elastic to a certain degree remember), and as they have damaged it, they will have to pay for the engineer.
Either that, or bend it back with the old 14lb sledge hammer.
DO NOT PUT ON KNOB OR BOLLOCKS!
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britishtrident
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| posted on 3/2/09 at 10:44 AM |
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Some mesurements and back of the envelope simple bending theory will give the numbers for the tensile and compressive plastic deformation strain.
But you would need tensile test result for the type of bolt in question to interpret the numbers.
What it really hinges on has the bolt been stressed beyond its yield point ----- yield point and the limit of elasticity are different on some
steels they are quite far apart, if they weren't stretch head bolts wouldn't work.
If that looks OK
They next part of the problem is to figure how the bolt material will behave when it is straighten and the best way to straighten it -- ie the
mechanical properties if the bolt is heat to red heat and cooled. For that you would need a metallurgist.
Because bolts have stress raising features ie the threads I would either apply a generous factor of safety to the results or get a finite element
analysis done by an a credited practioner.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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richardlee237
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| posted on 3/2/09 at 10:44 AM |
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The bolt has been plastically deformed and may have surface cracking and work hardening. The physical properties have been changed and no Qualified
Engineer would certify the strength. The other problem is that if you try to use as it is then the bolt will try to straighten leading to further
deformation etc etc.
If this is a real problem, then the simple answer is to diamond drill a core out of the concrete and fix in a new anchor bolt using a proper chemical
bonding system like Kem fix. It is relatively cheap and certifiable.
I have done this a few times when either the bolting pattern was not known before the foundation was poured, or there was a snafu like the one you
have. It is a perfectly acceptable system but casting in the anchor bolts is cheaper.
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
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iank
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| posted on 3/2/09 at 10:47 AM |
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If the customer bent it and are the worried ones then surely they will be expecting to pay for it to be corrected.
I'd put together a quote for fixing it properly (ripping out foundations and re-laying with new bolts etc) and the time it will take and let
them decide if they want to take the pain.
Anything else will require a proper structural engineer to estimate the load the bolt will be taking as a worst case - it's possible the other
undamaged bolts are enough on their own, but if not then it's going to be virtually impossible to estimate the remaining strength of a bent
bolt.
Bugger - too late again
[Edited on 3/2/09 by iank]
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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mcerd1
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| posted on 3/2/09 at 10:53 AM |
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quote:
Originally posted by yellow melos
or did sombody do somthing stupid to it.... like swing a 20 ton RSJ into it.
yeah something like that....
quote:
Originally posted by richardlee237
If this is a real problem, then the simple answer is to diamond drill a core out of the concrete and fix in a new anchor bolt using a proper chemical
bonding system like Kem fix. It is relatively cheap and certifiable.
I have done this a few times when either the bolting pattern was not known before the foundation was poured, or there was a snafu like the one you
have. It is a perfectly acceptable system but casting in the anchor bolts is cheaper.
we do these all the time too - but its too late now, and we are not doing the site work
quote:
Originally posted by richardlee237
The bolt has been plastically deformed and may have surface cracking and work hardening. The physical properties have been changed and no Qualified
Engineer would certify the strength
yeah - thats the problem
quote:
Originally posted by britishtrident
.....or get a finite element analysis done by an a credited practioner.
hadn't thought about FEM, but I doubt they'll pay that much or wait that long 
******
just to clear things up a bit
the structure is installed, it hasn't fallen down - but the end customer (our customers customer) is doing design asurance stuff
the structure is best thought of as an out door industial support (eletrical substation) so it has to support a fair moment at the base as its not far
off being a cantalever column
despite that the design load in the bolts themself is nowhere near the limit
btw - I'm an engineer (mech eng degree) but not chartered, so they will only be hapy with calcs (and as above no chartered engineer would touch
this)
[Edited on 3/2/09 by mcerd1]
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richardlee237
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| posted on 3/2/09 at 10:59 AM |
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You cannot assume that the foundation bolts are doing nothing other than locating the structure, without calculating the loadings.
It is quite possible to have an uplift on the structure due to wind loading or other dynamic loads imposed by machinery.
That said I have seen a lot of plant where the foundation bolts were not even tightened up or the nuts were missing completely and they had been
standing for years.
If you can determine the leg loadings either by calculation or by the original design calcs then you may be able to show the bolt is redundant.
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
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mcerd1
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| posted on 3/2/09 at 11:13 AM |
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quote:
Originally posted by richardlee237
If you can determine the leg loadings either by calculation or by the original design calcs then you may be able to show the bolt is redundant.
Loadings arn't a problem - I designed the structure
it has quite large moments (and some uplift under certain load cases) - these arn't your typical structures
I was comeing to that conclusion myself - but its not ideal as the next question will be "why were there so many bolts then if they arn't
needed?"
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r1_pete
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| posted on 3/2/09 at 11:14 AM |
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So the client is trying to pass the risk of failure onto yourselves by asking for the assurance.
I wouldn't accept that, I'd respond with - we can no longer guarantee the structural integrity, and some words around you bent it you
cough up for the rectification.
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richardlee237
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| posted on 3/2/09 at 11:29 AM |
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As you are aware of the design loadings and if you are confident that you have enough capacity in the remaining bolts then you can certify it. The
fact that you had surplus capacity in the system before the damage, was because your experience has shown that these things happen. Or words to that
effect. You can also point out that there is some remaining capacity in the deformed bolt as well.
This is when an Engineer has to have the courage of his convictions, training and experience.
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
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smart51
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| posted on 3/2/09 at 11:42 AM |
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quote:
Originally posted by richardlee237
if you are confident that you have enough capacity in the remaining bolts then you can certify it.
This sounds like a much easier tack to follow. If 3 of the 4 bolts fitted are enough on their own, it doesn't matter how much the 4th one is
weakened.
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BenB
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| posted on 3/2/09 at 11:44 AM |
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My attitude would be the same as when I lend someone a car:
you bend it, you mend it
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britishtrident
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| posted on 3/2/09 at 11:56 AM |
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The other approach of course is to straighten the bolt and get a pull out test done but the foundations might not have enough exposed area to take two
40 ton jacks and load cell.
If takes say 50% of UTS without showing more plastic deformation you have won a watch.
However if the bolt is bent through an arc of more than about ten degrees it is almost certainly beyond saving
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mcerd1
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| posted on 3/2/09 at 11:57 AM |
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quote:
Originally posted by BenB
My attitude would be the same as when I lend someone a car:
you bend it, you mend it
that would be nice, but they don't want to and we can't make them
they just want somone to say its ok in a way that they can prove (this sort of thing drives me mad, and they do things like this all the time  )
these are big international companies - they don't take any responsibility unless they have to and won't take my word for it either
without calcs to prove it
even if I was the world expert on capacities of deformed bolts they'd want calcs
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mcerd1
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| posted on 3/2/09 at 12:02 PM |
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quote:
Originally posted by britishtrident
The other approach of course is to straighten the bolt and get a pull out test done but the foundations might not have enough exposed area to take two
40 ton jacks and load cell.
If takes say 50% of UTS without showing more plastic deformation you have won a watch.
However if the bolt is bent through an arc of more than about ten degrees it is almost certainly beyond saving
its got to be less than 10 deg - they only had to drill the base plates 2mm oversize to make it fit (and its 25 or 30mm think I think)
I'll suggest a pull out test - but I'm not sure they'll want to take the structure down again......
they normally use 150% of the factored design load for pullout tests on chemical anchors so I guess they'd do the same here
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richardlee237
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| posted on 3/2/09 at 12:08 PM |
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This sort of situation is exactly what Project Engineering is all about.
It is very easy to say that it is the fault of the steel erector, crane driver or whoever and that they must put it right.
Are you really going to demand they dismantle the whole plant to replace 1 bolt ?
I don't think the client would too impressed or mcerd1's employer even though it would cover his a**e.
The Engineer has got to be able to demonstrate (either by calculation or physical load test) that the plant is still safe or not, that is why he is an
Engineer and not a steel erector.
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
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MikeR
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| posted on 3/2/09 at 12:11 PM |
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i can't follow most of this but ....
sounds like they know there is a problem and want someone else to say its ok - that way if its not ok, they get to blame someone else (and have taken
reasonable precautions if judges get involved).
be careful.
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britishtrident
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| posted on 3/2/09 at 12:15 PM |
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Re-thinking pullout test
simpler solution is a crane & load cell -- all thats required is some kind of special fitting to allow a pull to be applied directly to the
bolt.
[Edited on 3/2/09 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 3/2/09 at 12:30 PM |
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quote:
Originally posted by richardlee237
This sort of situation is exactly what Project Engineering is all about.
It is very easy to say that it is the fault of the steel erector, crane driver or whoever and that they must put it right.
Are you really going to demand they dismantle the whole plant to replace 1 bolt ?
I don't think the client would too impressed or mcerd1's employer even though it would cover his a**e.
The Engineer has got to be able to demonstrate (either by calculation or physical load test) that the plant is still safe or not, that is why he is an
Engineer and not a steel erector.
Reminds me of the Navies & Magnox nuclear power staion horror stories ----- When trying to increae the working life of these stations in the
1970s the engineers inspecting the pressure vessls foud unexpectedly severe corrosion on vital bolts and reinforcing bars
The cause was eventually tracked down by chemical analysis, the navies working at the top of the power station were not provided with toilets
facilities at the top so when they wanted to pee simple used the holes where long reinforce bars came up from the foundations. After the concrete was
poured the corrosive elements were trapped -- result a ticking time bomb that reduced the strength of the structure. The engineers then had to get
shed loads FEM analysis done very quickly.
[Edited on 3/2/09 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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MikeRJ
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| posted on 3/2/09 at 12:44 PM |
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quote:
Originally posted by mcerd1
[I was comeing to that conclusion myself - but its not ideal as the next question will be "why were there so many bolts then if they arn't
needed?"
Answer: I always in design adequate redundancy with these fixings since customers seem to regularly damage them during installation
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richardlee237
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| posted on 3/2/09 at 01:10 PM |
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The Construction Design Management Regulations require the designer to provide calculations of the plant loadings and design details and calculations
of the holding down arrangments. It is quite reasonable that the client asks that any deviation from the design is certified to be safe.
If they have specifically queried a bent h/d bolt then you have to assume that bolt is no longer any good. As you cannot calculate it, even by FEM as
you cannot certify the material.
If you really cannot certify the design with the remaining bolts by calculation then it is always possible to weld on an extension to the base plate
and bolt that down to the foundation. Thus restoring the original calculations.
The CDM Regulations were brought in to eliminate, amongst other things, the "she'll be right" attitude.
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
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