Static, Riks question and rebar question 1

[research09]

I am running a model of a slab, fixed on one end and i displace it on the
other end vertically. In the analysis, when the deflection is about 2
inches out of 20 inches I input, the model starts to rebound and rebounds
until the deflection is 1.5 inches in the other direction. Does anyone know
what's going on or had the similar problem?

The slab is of concrete with 1 rebar in it, if anyone has had success with
running a concrete with rebar embedded, please respond, I'm trying to get my
model to run through steel yielding.

Zach

 

[bassmanjax]

Could be that you've hit a point in the analysis where the structure is unstable. It can then react in one of two ways, in this case, the wrong way.

I've seen this kind of thing happen on some of my Riks buckling analyses - the job runs okay up to a point, and then for some inexplicable reason, the load starts to reverse and the structure deflects the 'wrong' way.

What I tend to do here is split the analysis into 2 steps - Step 1 is a *STATIC step to apply the preload and step 2 is the *STATIC, RIKS step to capture the non-linear post-buckle behaviour.

Another thing to try, if you have v6.7, is to run the job as a *STATIC step and use some STABILIZATION with the ALLSDTOL option. I've had some good results using this rather than RIKS recently.

Regards

Martin Stokes CEng MIMechE