anchor bolts too shor

huangyhg

anchor bolts too short
i visited a building construction site yesterday and was shown that the anchor bolts in a column baseplate do not extend through the baseplate enough to set the nut.  actually, some of them do not extend through the baseplate at all.  the problem appears to be that the contractor set the top of the pier too low (it would not be a problem if they were consistently low).  for some reason this was not brought to my attention when the problem was discovered, and now the rest of the framing has been installed.  this is a serious problem because these columns are part of a moment frame and the bolts are subjected to pull-out forces.  he has asked me what he can do the resolve the problem, either by welding the anchor bolts to the baseplate or by welding studs to the bolts and extending them through the top of the baseplate a sufficient distance to secure a nut.  what should i suggest that he do?
seems like a precarious place to weld...no room and little chance of inspecting a weld.  not to mention that this is critical for a moment connection and fatigue as well.
assuming that the pier is oversized, is it possible to jack up the column and slip a new, oversized plate undeneath the base plate which can be bolted down by drilling into the new steel plate and concrete pier and using expansion anchors or an appropriate concrete anchor.  the new, oversized plate can be welded to the existing base plate.
another alternate, in case the pier cannot accept a larger plate and bolts, may be to collar the existing pier with a steel plate.  the collar would be affixed to the pier by anchorages in the side.  the plate could then have appendages welded on the sides to accomondate new vertical anchor bolts.
interesting problem...waiting to see what other solutions are recommended.
sounds like you've got youself in a mess, not being an engineer type myself so i don't know if this would be an approved method, here goes.
i wouldn't recommend butt weldng the studs to the anchor, sounds like it would be a difficult position to get into and being able to produce a good consistant weld could be a problem.
presuming the anchor bolts are protruding a small amount what about making a base plate from say 1" plate and drilling holes to match the existing anchor bolt pattern, thru these holes the plate could be plug welded to the anchor bolts. this would require a welder with experience not to mention the correct documentation, cover thy a$% so they say.
before these plates are welded into place, plug weld studs so they protrude upward thru the plate and will give you sufficient length to do your bolting.
just my 2 cents worth...mike
i think that q has two good workable ideas there.  the option of sliding a larger plate with new hole positions below the existing plate is probably the best one, but the new plate will need to be thicker than the old one to carry the larger moment and prying forces generated in the new plate.
as another approach, how about welding triangular gusset plates to the column base in both directions.  the gussets would come wih their own base plates attached which carry new bolt hole positions.
another option (although i'm not convinced about this) is to grout in the existing bolts to ensure they can't move and then diamond drill out all of the existing bolts.  then grout in new ones in the same position.
i agree that you must nott attempt to weld extra lengths onto the existing bolts.
regards
andy machon
a variation on andy's gusset plate idea is to use a "bolt box" which is essentially an open faced box welded to the side of the column, 12 to 18 inches high through which a new bolt is inserted (all this after drilling through the base plate and coring into the concrete a sufficient distance to achieve necessary load capacity.  use structural epoxy to bond bolt to concrete) and nut placed at top plate.  technique is commonly used in tanks to spread load off the base plate and into the tank wall.  
i like q's collar idea also.  this puts the fasteners in shear rather than tension.  make sure the fastener depth picks up the rebar influence or you'll just shear a chunk of concrete off though.
welding to the anchor bolts can be done but it requires several considerations.  one, the "joint" is not a pre-qualified procedure and would have to be "qualified" through testing a similar setup in order to comply with aws (in us), cws (in canada) and likely other welding code bodies.  secondly, the "joint" would be a variation on a plug weld but would require tapered removal of the top of the bolt to affect proper weld access and provide some combined tension and shear mobilization in the weld.  nondestructive testing would then need to be done (angle probe ultrasonics)to verify weld integrity.  third, in welding, the filler metal and weld deposition technique should be selected such that piping porosity and other outgassing weld anomalies are reduced while still achieving adequate penetration and fusion. lastly, due to the thickness of the base plate and the anchor bolt, pre-heating and post-heating are likely necessary, particularly since the base plate is in contact with a huge heat sink (the concrete).
wish i had a nickel (well, ok maybe a buck...inflation, you know) for every time this has happened!
jamie2000,
hi!
the problem is a function of support depth or base type.
if you have the stanchion sitting on a column plinth and size of the plinth say about 350mm max. than you can drill through at sufficient depth and put in dowels of suitable diameter laterally. this dowel has to be checked for both shear and bearing. at plinth faces allow for cleats that can reach upto the stanchion. use suitable gusset plates to weld the stanchion and the cleats. ofcourse cleats, gussets and weld length and thickness has to be designed.

if it is resting on a base than it would be easier to use rawl bolts drilled  and set in epoxy. check bolt dia. for tension and anchorage. these bolts are to hold cleats maybe in 2 directions or all around depending on the pull out forces. again allow suitable gussets welded to both stanchion and cleats.
note the gusset shape is important for aesthetic purposes.
hope this is useful.
riz
why the heck don't general contractors bring these things to our attention sooner?  then they expect us to dig them out of the hole they put themselves into and want an answer asap.  i say have them go buy a new column or repour the pier.  the building is not what you designed or intended.  who's paying for your time to fix the mistake? if i sound a bit to bitter, please excuse me.  but i'm tired of having gc's coming to me to fix mistakes that shouldn't have happened if they would just do the job they're supposed to...coordinating the subcontractors and keeping an eye on the job instead of sitting in the job trailer drinking coffee and eating donuts.  i've only been in the business for 4 years and i feel i'm bitchin like some old grumpy se.  (or maybe just whining like a baby...  
the latter i think.
andy machon
moeit,
general contractors, for ages, have tried the patience of many engineers.  yes, they should be qualified to do the work and yes they should do the work as depicted on the plans but our industry mandates a quick and appropriate repsonse from the engineer in situations like this no matter what the cause.  usually, the general contractor's fix is based on convienence or expedience for that situation and ignores what function the designer meant for that detail to play in overall scheme of the structure.  as such, i am glad to have the opportunity to review those proposals and determine just what is appropriate rather than perpetuate the problem.
but it seems to happen more often than not.  is it approriate for me to tell them to make it right? to build it the way it was intended?  my reason being, is that i usually do not have the time to deal with these screw ups when i have 50 other things to do.  i don't feel comfortable just giving them the 'quick fix solution' they're always asking for.  it's my boss' seal that's on the line, and my credibility as an engineer.  i don't like being walked all over and i hate it when they tell me, 'you're holding up the job.'
when do they take the responsibilty?  it always seems to be my fault for not being out there to supervise them, my fault for not responding soon enough, my fault for not doing enough site visits, my fault for not catching it on the shops, i'm not the gc!  
i'm sorry if my venting is inappropriate.  i just want to know i'm not the only one.  and that as my career goes along it's not always going to be this way.
well said, q.
the construction process is not an easy one, just as design is not easy.  having experience on both sides of this table, i can say that we all bear responsibility for communication....communication of design intent (which is sometimes lacking), communication of lack of understanding of the design intent (just a simple question will sometimes suffice...the trick is knowing when you need to ask the question!), and communication of intolerance.  
most engineers are not "in your face" personality types and the result is a grizzled construction superintendent holding the high hand.  in my experience, construction people respect clarity.  when engineers respond to questions, all too often the answer is equivocal.  if you want a contractor to tear something out and start over, tell him exactly that.  just be sure you're right!  if you screwed up and didn't make your intent clear, work out a solution and don't complain about the question.  i get a bit wary when i don't get questions.  that means they think they know what i want.
and moeit, contractors are not slovenly idiots (well...there are some exceptions!).  in another 10 or 15 years, look back and see how much they taught you, either through overt competence or through inadvertent screw-ups.  you might be surprised.