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.
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The complex we were an owner at used cables in addition to rebar. It was my understanding that in addition to the rebar, there were tubes from side to side for the cables. After the concrete cured, the cables were tensioned to a very high force.
This was my balcony after the tile was removed. You can see where rebar rusts, it expands popping cement and tile. You can also see where previous management, prior to my purchase) decided to caulk the cracks with in-house maintenance rather than do a proper repair.
I was part of a very vocal group during the few years prior to this project, demanding work done by properly per engineering reports. While our board of directors berated us they at first claimed it was all 'cosmetic' Then spent two years trying to find an engineer that would back them up. The final engineer actually deemed my balcony as uninhabitable, removed and replaced the whole thing.
The final cost was over 8 million, including balcony repair, waterproofing and refinishing the exteriors, and replacing and repairing many of the columns in the lower level parking.