Precast Concrete Popping Noise 1

[MindofBarca]

Has anyone ever heard of precast concrete making a popping noise? I have read one other post on this forum and was not sure if they ever got to the bottom of the issue. I am an engineer at a precast concrete company and one of our customers called and mentioned 3-4 loud popping noises. He was not sure where the noises came from. Our hollow core planks were installed and grouted. I have heard of popping noises coming from slipping strands or over-stressed strands. Some other likely causes (from the other post) were thermal expansion and bearing pads not being installed correctly. If anyone has any insight or information it would be greatly appreciated. We are taking a trip to the job site today to see if any visual defects can be seen. Thanks in advance.

Jon

 

[msquared48]

Either thermal or shrinkage...

What is the application?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MindofBarca]

Here is the background on the project:

12" hollow core.
Dead load= 100 psf
Live load = 120 psf
Plank lengths = 43'-11"

It has been snowing alot, then warming up and melting. This project is in the Wisconsin area.
After visiting the site today we saw no signs of any physical damage. We talked to one of the site guys that was there the day of the popping, and he said this was no little pop. The site guy thought there was an explosion. He was standing next to the project when the boom went off and he said the boom made him jump in the air. There is one plank that stands out in particular, it seems to be deflecting around 1/2 to 3/4 of an inch. Which is odd considering the only loads that have been applied are a couple inches of snow. Any additional thoughts or concerns?

Thanks in advance,

Jon

 

[msquared48]

Deflecting up or down?

If it's down, I would suspect a ruptured prestress cable or anchorage, or two, or three or... This would definitely account for the loud popping.

If up, then inward wall movement at the plank end bearing locations, possibly due to backfilling?

Are the planks correctly supported?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

Are there any post-tensioned strands in these slabs?

BA

 

[msquared48]

These are hollow core planks BA, so, yes...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

Prestressed elements do tend to move up due to creep. Could it be that the planks tried to move differentially, stress was built up, then released by breaking the grout line? That would explain a very loud noise.

I have heard rifle shot type noises from post-tensioning strand breakage, and similar from release of thermal sliding stress at bearings, but those noises didn't sound like "explosions".

 

[BAretired]

I have run across hollow core slabs with pre-tensioning in the shop, but none with post-tensioning on site. If these have post-tensioning, I would suspect that each pop represents an anchorage failure.

BA

 

[msquared48]

Sorry BA, I overlooked the terminology. All the hollowcore I nave ever seen and used are post-tensioned in the casting bed, not on site.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[spats]

msquared,

I think the term your looking for is prestressed.

 

[msquared48]

OK... Picky, picky, picky...



Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MindofBarca]

The plank is deflecting, negative(positive would be camber). All of our hollow core is prestressed in our plant. All planks are correctly supported. They are supported by 12-14" thick poured walls with 4-5 inch ledges.
Thank you all for the responses. As of now we are going to wait for the snow to melt and look deeper into the grout key-ways and see if any cracking happened at the supports. If you guys have any other suggestions or comments I would appreciate them.

Thanks again,

Jon

 

[hokie66]

Mike, that is not picky. Hollow core slabs are pretensioned, not post-tensioned.

 

[JedClampett]

Might someone of adhered the flexible pads (intentionally or unintentionally) at the supports to the hollowcore. The popping could be due to the hollowcore rotation breaking the bond.