Using Concrete expansion anchor bolts to hang heavy weight from concrete ceiling/floor pad
I am on a job where we are being directed to install concrete expansion bolts into a concrete ceiling,insert pieces of 3/8″ all-thread into the anchors,suspend pieces of uni-strut attached to the all-thread, and hang a lot of weight from the uni-strut pieces. I think this is silly and dangerous. My understanding of these bolts is that their main strength is to resist shear or side to side forces, and live most of their lives just sitting there waiting for something bad to happen. I assume that their pull-out or uplift strength is kind of secondary considering that the main seismic stress these bolts are likely to undergo is side to side. Hanging pipes and ducts in commercial building is quite common, but the weight of what is suspended is much less compared to the application we are being asked to use the bolts for. This application also depends a lot on the integrity of the concrete and its resistance to breakout, an unknown because it is an old building. My understanding is that these bolts are not made to live their lives constantly under high pull-out stress. Any opinion or enlightenment you can throw my way?
Replies
This is done all the time when hanging sprinkler pipes (which are quite heavy).
I suspect that the type of anchor is important -- the "right" type is a sort of wedge that will simply become tighter due to pull-out stress. But of course a lot depends on the integrity of the concrete.
Is there an engineers stamp on the install plans?
Concrete wedge anchors and 3/8" all thread together seem to be mutually exclusive.
Maybe he means lead drive in anchors and all thread. That is more the norm, and 1/2" all thread would be a better choice . That is what is normally speced on wet system sprinkler installation, along with the proper spacing of course.
I've seen wedge anchors in many sizes.
So have you figured out what he is using? Anchor bolts or wedge anchors?
co-incidentally, there is another fellow here with the same problem - maybe you two can compare notes
http://forums.finehomebuilding.com/breaktime/construction-techniques/using-concrete-expansion-anchor-bolts-hang-heavy-weight-concrete--0
Are you talking about this style wedge anchor?
http://www.itw-redhead.com/trubolt.asp
Ever tried to get one of those out? I have. It wasn't possible without tearing out the concrete. The ones I had to get out, I just ended up cutting off. They were 1/2".
The question is ... who is directing you to do it? Architect or engineer. If so ... just do it; but make sure you do it the way you are directed. They are on the hook for the design, not you. You are on the hook to do it the way they specify. To second guess the designer is making a mistake. If not an architect or engineer is asking for this, you need to consult with someone that is to make sure the design is kosher. Small price to pay for your integrity.