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RE: Slabs on grade at garage and people doors

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If #1 implies that you are floating the slab everywhere except at door openings.  That doesn’t seem logical and sounds like a shrinkage crack waiting to happen across the doorway, or, if you reinforce it, someplace else that’s nasty and surprising.


IMO, perimeter anchorage of slabs to walls is probably the most dangerous aesthetic consideration in all of concrete er, “slabdom”. 


I’m a really big fan of 3 or 4 foot wide perimeter slab pour strips in nearly all situations and not less than about 3 weeks after the main slab is poured.  That way, the connection to the walls becomes less important.




From: Jim Wilson [mailto:wilsonengineers(--nospam--at)]
Sent: Tuesday, January 08, 2008 9:04 AM
To: seaint(--nospam--at)
Subject: Slabs on grade at garage and people doors


I'm looking for some opinion about slabs on ground at door openings - Which detail has more pros or cons?  Are there other details that perform better than these?


The typical slab detail in this case is to have an expansion joint at the perimeter to allow it to float inside the foundation wall.

1. Drop foundation wall at door 8"-12", extend slab over and pin to wall with reinforcement bent out of the wall and into the slab.

2. Drop foundation wall at door 8"-12", extend slab over with a horizontal slip joint between the wall and slab to allow the slab to shrink unrestrained.  Additional reinforcement to be provided in this section of slab to mitigate cracks.


This is in non-seismic areas, northeast U.S., light to heavy commercial use.



Jim Wilson