Tension Reaction in Nodal Support able to Uplift

[Anonymous]

Hi Guys,

I am modelling a foundation which sits on piles. The reinforcement arrangement does not transfer any uplift into the piles. Its an eccentric foundation with a high overturning moment.

I have modelled the foundation slab as a plate with the piles as nodal supports. The nodal supports are shown allowing uplift in +z and have a defined stiffness in the -z direction.

I have run as a non-linear analysis and everything appears to be converging.

However in certain load combinations I appear to have reactions at the nodal supports which are negative. The displacements appear to be OK (i.e. uplift appears to be allowed) but the supports still seem to be carrying a reaction.

I attach some screenshots showing model and the support conditions overlayed against the reaction table for the combination with negative loads.

Have I done something stupid with the support conditions or any other advice you can provide would be good.

[Rafal.Gaweda]

Robot file please.

[Anonymous]

Sorry should have attached first time.

Saved without results.

[Rafal.Gaweda · Accepted solution]

I do not think you get any reasonable results with "your" nonlinear settings.

See below - correct results with correct nonlinear settings