multi storey underground parkade clear cover

[gagne73]

I have a underground parkade to design, with 2 storeys below grade. At this point I am getting a headache trying to determine my clear cover for all reinforcing within the structural slab.

It appears that according to Table 17 (CSA A23.3#-14) tells me I MUST have minimum 60mm concrete cover for all beams/slabs/columns, solely based on the type of exposure that I have. This, conveniently also satisfies requirements I have for 4hr ratings as well. For the beams, does this mean cover to the stirrups, or to the primary beams?

big question I have with that, is would you follow these covers for the upper structural slab as well? THe structural slab has parking BELOW it, but is commercial space directly on top. I am undecided of my exposure for that slab, as it doesn't have direct exposure to chlorides, but it will be humid from time to time, with more corrosive air.

Another issue, is that having 60mm of cover makes me a little bit concerned about cracking, is this legit?


I would really appreciate a bit of a response from somone with more parkade design experience. I havent really been able to find quite what im looking for on here, although there are similar posts. Its pretty important, as having 60mm cover on both top and bottom of slab makes for a thicker slab/beam for sure.

 

[gagne73]

sorry to do this guys, but I posted it late in the day yesterday, any one on here today with any experience with this?

 

[sandman21]

The clear cover is to the first rebar, so stirrups in beams/columns/walls. Typically the cover requirements apply to the side exposed to the condition, weather, water, hazardous materials etc. Have you never run across 2.5"(60mm) clearance? It will depend on the application and how sensitive you are to cracks. Generally, I would not be concerned about the increased depth

 

[gagne73]

thanks sandman,

Iv had that cover, but not for structural slabs where cracks would be visible.

I wasnt concerned about it until one of the threads on here i read, a few people were freaking out about having too much cover. tho frankly, I would prefer a few hairlin cracks vs seeing the rusting reinforcing within 10 years becuase of only having an inch of cover

 

[BUGGAR]

We typically specify 3" cover on marine structures. Cover is to stirrups or nearest steel. This is severe exposure.

 

[sandman21]

The mix, amount of reinforcing, and most importantly the placement and curing will have the most impact on the visible cracks in concrete.

 

[SkiisAndBikes]

In Canada I believe the durability, i.e. cover, etc.. requirements are governed by the CSA S413 design standard, which is an add on to A23.3 and A23.1 specifically for parking garages. The clear cover you are required to have is stipulated in this standard and will vary depending on what type of waterproofing system is specified, whether a corrosion inhibiter is used, whether the bars are epoxy coated, etc... If you are designing parking structures in Canada, the S413 standard is a must have and will clarify your question.

 

[gagne73]

thanks SKis. I do have that standard, but frankly, the cover required from fire rating, and table 17 of A23.3 are more stringent than the parking structures code, which would mean table 17 governs regardless I believe