Construction Joints in a Mezzanine Slab
Construction Joints in a Mezzanine Slab
(OP)
Structural Metal Decking, bar joists 5' on center, 4" thick slab on deck.
50,000 sq ft so we are required to make sepearate pours. Where and how should we make construction joints at pour stops?
50,000 sq ft so we are required to make sepearate pours. Where and how should we make construction joints at pour stops?






RE: Construction Joints in a Mezzanine Slab
Perpendicular to the joists - anywhere as this is parallel to the span of the deck/slab system.
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RE: Construction Joints in a Mezzanine Slab
RE: Construction Joints in a Mezzanine Slab
Two additional bits of advice:
1) Most people keep construction joints away from welded studs if present. Probably not an issue with joists.
2) You may want to stitch the slab together across the joint with rebar to restore diaphragm continuity.
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.
RE: Construction Joints in a Mezzanine Slab
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RE: Construction Joints in a Mezzanine Slab
The Architect changed from floor covering to stained and sealed exposed concrete, therefore we're trying to elminiate as much of the random cracking as possible. From everything you've helped us with we're going to use slab boosters in the thick areas of the decking to keep the wire mesh at the top to help with cracking, and eliminate as many construction joints in the stained concrete as possible.
Thanks again!
RE: Construction Joints in a Mezzanine Slab
For slabs-on-grade (which you don't have) you get the drag from the subgrade resisting the shrinkage and thus shrinkage cracks.
For elevated slabs on metal deck - there is still some degree of shrinkage resistance due to the deck flutes, deck-concrete bond, etc. but you also have a much higher variability in vertical stiffness across the slab due to the change in flexibility of members (more flexible at midspans ans with lighter members - less flexible near heavier girders or columns).
These flexibilities will cause cracking as well.
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RE: Construction Joints in a Mezzanine Slab
Nowadays, if I have composite deck systems that are exposed or overlain with sensitive material, I specify 15M@400 EW everywhere at minimum. I know, it sounds pretty extreme. This is commensurate with the extreme displeasure that my client communicated to me when I messed this up. I expect that a heavy safe or filing system could produce a similar result.
If you place your construction joints at the supports, I’d recommend this at minimum:
1) Either construct a hard joint with no rebar or concrete crossing it or;
2) Install some real top steel across the joint and be generous with it.
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.
RE: Construction Joints in a Mezzanine Slab
RE: Construction Joints in a Mezzanine Slab
koot - Do you typically provide top bars perpendicular to, and over top of, the beams for slab on deck? That's a typical detail we use to control the exact cracking you described.
RE: Construction Joints in a Mezzanine Slab
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.