Anchor bolts too short 9

[jamie2000]

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?

 

[IJR]

This last post can not pass without my support. One of the best input for the rest of us in this profession, keywords being "dreading phone calls" from sites(with consequences like bad stomach and pointing fingers to others).

What makes someone a good engineer is how he lives with his design. Whether it works out fine at site or not, you should just go and live with it and be able to enjoy doing that too. Sometimes I have found that though sites did well with my work I could have done better with a small change in design.

My respects
ijr

 

[elpoblano]

Jamie200,

Another proven solution (have done it many times with corroded, off-plumb and short anchor bolts) is, to completely cut off the existing a. bolts leaving enough projection above the concrete (if necessary remove the concrete to a lenght were welding is conforta ble and repour the pier later) to weld a new section of the same type of rod. The welding shall be complete penetration groove weld and sized to take the same stresses than the original a. bolt.

Why so much reluctancy to weld an extension to the a. bolt? There used to be a standard for welding rebar and a. bolts, but I can't find it. It was an old CSA one, so anybody knows what is the new standard?

Ensure that your new a. bolts are plumb and will not deviate from it due to the welding residual stresses. You can tread your new a. bolts after cooling. Install your column, plumb it and place your grout.

It sounds like a lot of work, it is not, and it is a very cheap solution too.

If we are to be philosophical in every single tread in this website there won't be enough disk space for it. An engineer's merit is to keep focus, TIPS only please!

 

[Tomfh]

Here's a link about couplers and welding extensions:

http://www.aisc.org/Template.cfm?Se...omSource/FAQContentDisplay.cfm&FAQID=985&TA=1

If you want to weld make sure the bolts are weldable!





I'm only a new engineer but in my short career I have been warned about problems with cast in anchor bolts many times. I've heard people say chemical anchoring is better, since it is so much easier for the boys to get the positioning correct.

What do you guys think of chemical anchoring for hold down bolts?

 

[Stress02]

Doesn't the amount of heat that will be imparted to the original anchor bolt when welding create a potential for cracking the concrete?

I have always resisted welding for that reason.

 

[epr]

I wonder if Jamie2000 is still around. His question is now approximately 5 years old, and answers are still coming !!!
This is, however, a good opportunity to explain a project where we had 2" diameter high strength anchor bolts that were just long enough to be a couple of threads short of reaching the top of a single nut. Although it is not recommended, we welded the anchor bolt to the nut as a last ditch effort. I explained to my client that if it did not work, the structure (which was installed before I was called to inspect) would have to be taken down, the foundation would have to be modified, and new anchor bolts installed (a very expensive process).
I do not remember all the details (it's been about 10-12 years ago), but we pre-heated the base assemblies to a few hundred degrees for a period of time and then performed the welding. It was a slow process , but it did work well. Testing (dye penetrant and ultrasonic) confirmed that no damage existed after the procedure was complete.