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Slab Pinched by Structure

Slab Pinched by Structure

Slab Pinched by Structure

I was always taught to never pinch a slab with structure that is carrying load from above.
The reason being that the column or wall would be separated from its bearing support by something that was not designed to be "in the way".

In addition, I have seen slabs sag out as a result of poor compaction, slab construction problems and water leaks below slabs.
When the slab sagged, it acted like a crow bar and sent distress through the entire house in the area of the column. I have seen
this more than once.

When I point this out to other engineers and builders, they look at me like I am crazy. I tell them, "This is not something I read in a book. I have seen it"
They squirm a little and re-evaluate their years of slab pinching projects and experience.

I just want other's take on this common construction "issue" which seems pretty clear cut to me, but is apparently "way over the top" to a lot of
guys I'm meeting in the industry.

The slab I'm speaking about is a typical residential, 4"thick, WWF reinforced, fancy floor covering. It is not designed to span anomalies and is not reinforced
with bar. It simply separates people's feet from the gravel and dirt below.

RE: Slab Pinched by Structure

What does "pinching a slab" mean?

RE: Slab Pinched by Structure

I've never given this much thought. Most commonly, I terminate slabs on grade at the side of walls and grade beams and only run the slab over top of those elements at doorway conditions. And, at those doorway conditions, there will be a local slab thickening and some L-bars into the structure below. They're not really designed to be the in between thing but they're detailed appropriately in my opinion. For architectural reasons I have, on occasion, run slabs on grade over frost walls and an inch or so beneath walls without doweling in so as to hide the joint. I haven't been made aware of any problems so far.

To some extent, what you're considering to be a detailing failure could also be viewed as a geotechnical failure.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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