Modeling a Fdn Wall braced by a Wood Floor

[bigmig]

I am slowly improving my Risa 3d skills and have come to the situation where I'm trying to model a common residential basement retaining wall that is braced by the slab on grade at the base (basement level) and a wood diaphragm at the top. What is the most accurate way to do this? The wall is a plate model (1'x1' squares).

One method I used was to model small rigid links that held the top of the wall from rotating. Each link in turn was supported by a compression spring with a stiffness that I basically guessed at. Probably not too accurate.

I'm guessing that I will have to model the diaphragm stiffness correctly (Breyer 6th edition will help with this), but I'm not seeing how I tell risa what this stiffness is.

Someone posted the following comment on another risa discussion regarding a veritical wood shearwall, which I think would apply to my situation:

"you MUST model for the shear stiffness "G", rather than "E". (You cannot model for both. The plate algorithm can't handle a poisson's ratio greater than 0.5 - choose "G" and backsolve for an "E" value based on a "normal" poisson's ratio of about 0.2)"

Can anyone expand on my problem or this statment?

 

[JoshPlumSE]

Bigmig -

Actually, it's the opposite. The plate element formulation uses only the E and v values. Therefore, if you've got a G value (from the plywood design specification or some other reference) then you need to convert that into an equivalent E value.

The equation for isotropic materials is
G = E / (2*(1+v))

Also, the next release (version 8.0) allows different values of E and G so that you can get orthotropic behavior of your plate elements if you like.

 

[JoshPlumSE]

Bigmig -

Reading you message a bit closer I have something else to add. The "diaphragm" feature in RISA is a fully rigid diaphragm. It's stiffness cannot be adjusted to give you semi-flexible behavior in the way that you describe. Instead, you have to model the diaphragm using a mesh of plate elements. I hope that helps!