Shear stregth

[ghcaste]

Hello,

I would like to know why it appears to be a big difference between the shear strenght calculated following the american code compared to the shear strenght calculated under the canadian code:

American code: Vc=2*0.85*√f'c
Canadian code: Vc=0.65*β*λ*√f'c
where β is around 0.2 and λ=1.0 for normal density concrete, so basically we have:
American code: Vc=1.7*√f'c
Canadian code: Vc=0.13*√f'c
Big difference!!!

Thanks in advace for your help!

 

[Teguci]

Its the cold weather, eh!

ACI is 1.5*√f'c and is in psi units. Aren't you guys using metric?

 

[ghcaste]

Thanks Teguci, yes, we are metric but I thought that was given regardless the units... well, it makes sense but I will verify it by myself... might be the cold weather too..lol
Thanks again.

 

[BAretired]

There is very little difference. The square root skews the result.

BA

 

[IDS]

The difference in this case was (mostly) due to the units, but there are big differences in results depending on which provisions of which code you use.

Shear design is over-simplified resulting in unreliable results.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[BAretired]

The main reason why concrete shear design is over-simplified is that nobody fully understands how and why shear failure occurs.

BA

 

[Robbiee]

The Canadian A23.3 simplified method used to be the same as the ACI method. The current two methods of the A23.3 are different and are base on the Modified Compression Field Theory developed by Collins and Mitchell in 1980. These two methods, i.e. the Simplified and the General method, relate the shear strength of concrete beams to the longitudinal tensile stain, and that why Beta is there. So, a section subject to shear and bending moment will have lower shear strength than the same section without moment. ACI, I believe, has another method to account for the effects of bending moment and tension on shear strength.