Isn't the clear cover of 4 cm that is required by ACI for columns excessive?

[T2ioTD]

I find a clear of 4 cm for columns too much: often residential columns are narrow to fit into wall partitions (at least in the middle east), and taking 4cm + ties diameter from the effective depth will leave the column weaker and requiring more and more steel.

In Eurocode the normal clear cover is 2.5 cm, if I understand properly.
In BAEL (old french code) it used to be 1.5 cm.

What do you think?

 

[centondollar]

The clear cover is a function of many parameters (concrete strength, exposure class, rebar etc.) in EC2; it varies from +10mm to +50mm, and >70mm for slabs on uneven ground. Follow the code and you will find that 40mm cover, including the 10mm deviation, is not much at all. Furthermore, for high fire ratings (say, R90 or R120), the required cover is also often more than 40mm.

If the columns to be designed are for residential (low-rise) use, the amount of rebar is small in any case, and sufficient cover will present spalling and corrosion.

PS. I would recommend designing to code unless you can prove that a smaller cover is sufficient. Usually, proving something takes more effort than referring to the standards applicable in your country.

 

[OldDawgNewTricks]

Another factor to consider is the consequences of failure of a primary structural element such as a column or girder. Failure of such members is likely much more catastrophic than failure of secondary members such as slabs, joists, or walls that have more redundancy to redistribute loads. Therefore, a little extra conservatism is warranted to protect these primary members from corrosion, fire, etc.

 

[Lomarandil]

If your project is tied to a code, follow the code (as centondollar suggests).

If there isn't an applicable code, sure, it's worth knowing how different codes approach the issue. But in the end, somebody needs to decide what code to follow and apply all of those provisions. You really don't want to mix and match detailing.

I'm in a case where no building code is mandated. I tend to use ACI, because I'm familiar with it. As such, I design and call for 40mm as the default.

Now, knowing that Eurocode allows less cover, and knowing that the risks of low cover (exposure, spalling, material properties, fire resistance) are minimal for most of my projects, I don't raise a big issue if I notice 30mm spacers used in the field (again, project by project basis). But if I were counting on the strength benefits of less cover, I'd recalculate according to Eurocode to make sure it works under that method.

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just call me Lo.