Hanger problem with Autoclaved Aerated Concrete

[SprinklerDesigner2]

I have two motels built with Autoclaved Aerated Concrete

http://www.xella-usa.com/html/us/en/index.php

with sprinklers per NFPA #13R.

These hotels are the first structure of their type in Georgia.

I was concerned about hanger attachments so I visited the factory where I was presented with a list of "approved" hanger materials but they all utilized plastic inserts with maximum weights being 150 lbs. The only exception was you drilled through the concrete plank, countersunk a hole at the top then secure the rod using double nuts and washers. As the building has a standpipe I utilized this method for hanging all pipe > 2".

Explaining the problem the shop foreman and I experimented using Sammy screws. The first one we used was a concrete Sammy

http://www.sammysuperscrew.com/CST.htm

but it pulled out. Next I installed a 3" wood Sammy

http://www.sammysuperscrew.com/GST.htm

and, properly installed, it worked just great. After installing a 3" wood Sammy we hoisted the plank up on a forklift and three of us tried to pull it out and couldn't. Hanging weight was >650 lbs and trying our best to make the hanger fail all we succeeded in doing was deforming the band hanger.

Not exactly an engineering study I was satisfied the hanger would be adequate as long as our guys installed it correctly ie don't bottom the hanger out.

The first foreman we sent on the job thought it was better to use concrete Sammy's without talking to me about it. Not having the proper tool to install he used a regular ratchet, over spun the Sammy resulting in a number of them pulling out. I corrected the situation, changed the hangers to the 3" wood Sammy, installed over 700 and not a single one pulled out.

Word got out to the project engineer about the first hangers pulling out and now I have a problem. Explained the situation, that the first hangers were for concrete and improperly installed but he's not liking any of it now. The only alternative is replace all the hangers with rod drilled through the plank and double nutted.

I see the engineers point, the wood Sammy's are listed for wood, not Aerated Concrete.

Stuff cuts like butter, you use wood saws and drillers for holes and it takes about 30 seconds to drill so it isn't the end of the world if we have to do this. I figure it will take three guys a week so it isn't like I am trapped with nowhere to go.

I take it demonstrating the hanger is capable of holding 5 times it weight (mostly 1" CPVC) plus 250 lbs is not acceptable?

Thoughts from PE types would be most appreciated.

Thanks.

 

[trashcanman]

I would never allow drilling into a concrete wall or floor. Let the Structural Engineer make that call. That is what he/she is for.

 

[SprinklerDesigner2]

Trashcanman,

I couldn't agree more and we have had the OK to drill through the floor from start of project.

Monday morning I picked up an Autoclaved Aerated Concrete block from the manufacturer and overnighting it to Sammy Screw's engineering department. The engineering department is going to subject the hanger to pull out tests and whatever else they do. Once tests are completed they will write a report which I will forward on to the structural engineer who has indicated he will accept it.

For what it is worth we've installed 700 of these hangers and given instructions to our fitters to hang both their combined weight, this is about 550 lbs, to each and every hanger and so far not a single pullout.

At this point I really don't care, if we have to drill and double nut, this method is explicitly allowed by the aerated concrete manufacturer for weights up to 1,000 lbs, but if the Sammy failed it wouldn't be the end of the world right now. This stuff drills like soft wood and I am confident three guys could change out all the hangers in three or four days. An extra 72 to 96 man hours on > $200k worth of work wouldn't be the end of the world.

What I don't want to have happen is to have the floors finished, carpet down and walls painted to have the problem rear its ugly head because then I would have severe problems. At that stage I can easily see where the fix would cost several times what we sold the jobs for.

Now I am thinking even if I do get approval it might be prudent on my part to just drill through, double nut and be done with it.

 

[stookeyfpe]

SD2:

When you are talking to the folks at Sammy Screw, you may want the firm preparing the concrete to dialogue with each other to discuss long term issues as it relates to corrosive action between any the metals used in the alloy used to manufacturer the fastener and the materials formulated to batch the concrete.

I'm sorry I didn't post an answer earlier. But I have been thinking about your problem. For example, I'm assuming the sprinklers are installed indoors. However, is the hotel close to the coast, where salt air could potentially accelerate the corrosion of the Sammy Screws, resulting in a premature failure?

 

[SprinklerDesigner2]

Stookey,

Thanks, I'll bring up the corrosion.

For what it is worth these projects are 70 miles inland.