Quote:
Originally Posted by ckissick
Here's my guess as to how it failed.
I'm assuming the floors were post-tensioned slabs. During construction, you lay out the rebar, then use hydraulic rams to pull them tight, like guitar strings. Then you pour the concrete and let it set. Once set, you release the tension on the rebar. It tries to relax, but transfers the stress to the concrete, making it tight and rigid.
Now, let corrosion begin. If the rebar rusts, it loses its grip on the concrete and the whole thing loosens and weakens. The slab is no longer able to hold the load and fails.
|
The cables come with a plastic sleeve around them. The cables are laid in the formwork and then the concrete in placed. The cables are tensioned AFTER the concrete is placed. They are pulled a few days after the concrete is placed. I worked on 3 post tension projects when I was younger. I actually was on the crew that pulled the cable with the jacks. It is very important to grout the ends of the cables at the slab or beam ends. It seals the cables.