Uplift nodal supports

[RRufino]

Dear Sirs,
Please help me understanding the following. For a very simple structure i was trying to use pinned supports allowing uplift (see images below). Even so, looking to Fz reactions, i’m getting negative reactions (restriction to uplifting), also in same cases i’m getting downward vertical displacements instead of upwards.
Is this a bug or I’m not understanding the expected behaviour?

Please find model in attachement.

Thanks in advance,

RR

[DennisVDijk]

Hello @RRufino,

If you use the uplift function you have to give in a spring value for the direction the uplift is applied, see picture below:

check also the help article: https://help.autodesk.com/view/RSAPRO/2025/ENU/?guid=GUID-B4798AE8-5A5F-4986-BE29-B292975687BA

model attached.

[Rafacascudo]

@DennisVDijk 

Elastic supports Not needed for a regular load case or combination when having uplift supports. Do not know  for other types like seismic

[Simau]

Hi @RRufino 

I agree with @Rafacascudo about elastic supports

I have 2 remarks concerning your model:
- Modal analysis cannot be done with a non-linear structure
- your seismic combinations only include the earthquake efforts without any additional vertical load cases such as dead loads.
So i have redone your model:
- by simulating the earthquake as a horizontal load applied at the top of the structure
- by using new combinations (according to Eurocode 0)
No inconsistency in displacements and reactions for supports with uplift

[RRufino]

Dear @DennisVDijk , @Rafacascudo and @Simau thanks a lot.

@DennisVDijk and @Rafacascudo should i conclude that the following support message (click) only applies to "static" load cases?

@DennisVDijk regarding the model you kindly attached, you have supported nodes with displacement uz<0. It's not what i was expecting, am i wrong?

@Simau, i think my model is according with eurocodes (EC0+EC8). Seismic combinations are defined on cases 25to40. All of them are combined with seismic  newmark actions (cases 12to15 and 18to21) and quasi-permanent load combination (case 22). Maybe it's not correct to nonlinear combinations (?) but i think this procedure is correct for linear analysis, right?

Thanks again,

RR

[Simau · Accepted solution]

@RRufino 

You are rigth case 22 = cases 1 + comb 7 = 1 2 3 4 cases.

I was a bit lost as i didn't now what are these case represent; That why i created combinations again.

The only problem is you can't use modal analysis with a non linear structure, seismic and Newmark combination will nt be corretc