Horizontal reactions due to vertical loads

[mammut]

Hi,
I'm calculating anchor bars for concrete shear walls.
When there is vertical load applied to the top of the wall we get horizontal reaction at the bottom (see the image). Logically the sum of those forces must be 0 as they have opposite directions so there is no need for anchor bars due to these loads.
But in the FEM model total reactions that I'm getting seems to be too big just for the wind load. So i susspect that that it's somehow related with vertical loads.

The question is - what is the common way to deal with the horizontal reactions coused by vertical loads? And maby some suggestions for the publications regarding this issue?

Thanks,

Janis

 

[jayrod12]

Wait. Why are you getting horizontal reactions from vertical only loading? that seems unlikely. Poisson's ration for concrete is so low that it shouldn't be a considerable amount of restraint required to overcome the expansion laterally due to the vertical load.

How are you modelling the base of the wall? single pins on each end? fixed on each end? a bunch of equally spaced pins? a bunch of equally spaced fixed boundaries?

 

[mammut]

Hmm,i'm a bit lost now.
Yes I understand that horizontal reaction depends on the poisson ratio. I have it 0.2 - as for uncracked concrete.
That is not correct? For cracked concrete its 0, in that case horizontal reaction will be 0 as well..

Wall is supported by 'bunch of equally spaced pins'

 

[jayrod12]

I would put my money on your wall being more likely to expand in thickness than in length due to poisson's ratio. That would bring your horizontal reaction down.

Also once the wall tried to expand there would likely be micro-cracking and would then render it cracked concrete. At least that's how I would rationalize it in my head.

In a purely vertical load scenario like this one I never would've considered any horizontal force component. I would've provided some sort of dowelling to the base but likely not have run numbers on it.

However, as you mentioned, these are concrete shear walls. You WILL have lateral loads applied on them and as such you will need to provide a quantifiable connection to resist this lateral shear load. It is likely that this requirement would control the design. The shear wall action will also cause cracking in the concrete which further reinforces neglecting poisson's ratio.