Concrete Column Shear

[rory01]

In concrete column design, with negligible moments and shears applied i.e. say uniaxial compression, would we check for the maximum shear stress resulting at 45 degress due to the compression? What would be the allowable?

 

[RiBeneke]

In concrete design to BS and SABS etc, we would not check for shear at 45 deg to the principal stress.
In this respect concrete design has been simplified (unlike soils design) and checking against the allowable compressive stresses is what is required.
If you watch a concrete sample failing in a compression testing machine, it actually fails in a combined tension/shear, but the corresponding compressive stress is what is measured and this is used as a basis for design.

 

[rory01]

Ribeneke:

Cylinder test for uni-axial compression should not experience tension and thus the failure can be shear with compression. Depends on material - i.e. weaker in shear than compression. But, knowing this about a material we can limit the allowable design compression to preclude a shear failure.

 

[RiBeneke]

I was referring to the way a compression test sample often splits on a vertical plane. To me this suggests an internal tension stress that is perpendicular to the vertical compression. But perhaps I am just misreading the shear failure that also occurs simultaneously.

There probably is some relationship between pure shear failure and compression cylinder results. Certainly the allowable shear stresses in a beam are based on specified concrete compression strength.