Cast-in-place (Nonprestressed) concrete cover
Cast-in-place (Nonprestressed) concrete cover
(OP)
For concrete elevated slab above parking garage, what is the bottom concrete cover? Can I assume the concrete is not exposed to weather or in contact with ground? Thus, 3/4" cover.






RE: Cast-in-place (Nonprestressed) concrete cover
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
Mike McCann
MMC Engineering
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
The amount of times I seen the underside of a slab have cancer issues as opposed to the top side is too numerous to count on two hands. I believe that is has to do with wetting and drying, the top side gets cleaned during the rain event while the bottom side gathers all the dust, chemicals and other not so nice corrosive agents. Then you have all the active ingredients for a nice injection of cancer. If the top of the slab isn't seal 100% the water will get to the bottom side and create nice damp places for all these ingredients to activate. This of course it relevant for open garages more than enclosed garages and does depend on you top labs water proofing.
The next point I will make is don't spec ¾" agg, this is to large for ¾" cover if you are going to adopt 3/4" cover. I would recommend a minimum of 1" such that the agg can get under the reo/ducts.
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
Unless there is some super stringent architectural or serviceability issue, I do not see how it will make much of a difference
-Robert Miller, E.I.T.
KPA Structural Engineers
RE: Cast-in-place (Nonprestressed) concrete cover
I would say that if the concern is for moisture from the top of a slab getting thru to the bottom reinforcement then the problem isn't with the cover on the bottom of the slab. In that case the cover for the bottom reinforcement from the top of the slab is relatively large. Increasing the bottom cover won't help with that problem.
RE: Cast-in-place (Nonprestressed) concrete cover
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Cast-in-place (Nonprestressed) concrete cover
Increase the cover since the "exposure" condition is greater than the static minimum condition would imply.
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
Actually, for conventional concrete, the cracks/control joints should be properly located and sealed. If you have an exposed deck, proper maintenance requires the sealing of unwwanted cracks to prevent deterioration.
For a PT deck, you better not have any unwanted cracks. Otherwise you didn't do your job.
RE: Cast-in-place (Nonprestressed) concrete cover
RE: Cast-in-place (Nonprestressed) concrete cover
This tells me that most parking garages which do not have covered or sealed top decks would require increased cover. Water can be carried into garages on vehicles and by wind in sufficient quantities to induce corrosion.
Also a parking garage in an area where salty ice/water is carried in on vehicles might need to be designed for ACI 318 Table 4.2.1 exposure category C2 (severe for corrosion protection of reinforcement.) This requirement is frequently overlooked.
RE: Cast-in-place (Nonprestressed) concrete cover
@Hokie - since concrete is usually a water saturated environment for reinforcement, it is not the water exposure that causes corrosion of steel. It is the water in combination with a contaminant (typically chlorides). The better strategies are geared at limiting rebar exposure to chlorides (and other contaminants).
For top rebar this includes cover, tighter concrete (usually with higher strength, fly ash or GGBFS), corrosion inhibitors (DCI), and the sealing/limiting of cracks.
For bottom reinforcement, bottom cover doesn't matter for chloride attacks (water carries the chlorides down) unless you are in a surf zone (New York is not). The worst I can think of would be carbonation from the underside due to high CO2.
@TXStructural - How can you make the statement "This requirement is frequently overlooked"? This table is new (2008) and just now being adopted by building codes.