topic Re: How to model tension only springs with some pre-stress in robot? in Robot Structural Analysis Forum

How to model tension only springs with some pre-stress in robot?

muhammad_hasan88NXQ — Fri, 08 Mar 2024 06:41:14 GMT

Hi Guys,

I need your help with modeling of ground anchors which are prestressed with a force of 800kN. Is there any way to model them as tension only springs in robot where there is No movement till the tension of 800kN in the spring after which the springs displaces as per the assigned stiffness.

I have tryed Non linear spring with rigid with linear hardening but it is throwing convergence error.

I am attaching my model for reference. please help.

Thank you.

Re: How to model tension only springs with some pre-stress in robot?

Simau — Sat, 09 Mar 2024 16:53:29 GMT

Hi@muhammad_hasan88NXQ

To simulate ground anchors add 800 kN as selfweigth load

Furthermore for the NL analysis parameters, check the “Matrix update after each iteration” box

Re: How to model tension only springs with some pre-stress in robot?

muhammad_hasan88NXQ — Mon, 11 Mar 2024 04:25:55 GMT

Hi Simau,

Thanks for your help, but that is not working. we are expecting reduced displacement at the top of 75mm which we got from another geotech analysis software. and gradualt increase to max of around 95mm as shown in pics.

And also the model is showing convergance error for selfweight. I have tryied providing PT force in Selfweight case and also soil load case both where giving same results.

Can you please help me

Re: How to model tension only springs with some pre-stress in robot?

Rafacascudo — Mon, 11 Mar 2024 19:14:24 GMT

I applied the 800kN prestress loads directly to the 8 nodes , same as @Simau did on the previous post .

But instead of a nonlinear "equation" support , I just applied an regular elastic with uplift support using the "k" value of that "equation" as the spring value on each of the 2 different Nonlinear supports respectively

And then on the nonlinear parameters on Analysis options , I set it to apply all the load at once , checked the usual trick to make it converge faster that @Simau suggested and increased the tolerances a little bit.

0.001 for SLS and prestress cases and 0.0017 for SW

and I got these displacements for prestress load case and SLS combination (max=63mm)

Model attached

Re: How to model tension only springs with some pre-stress in robot?

muhammad_hasan88NXQ — Wed, 13 Mar 2024 00:23:30 GMT

Thank you Rafa for your help, but the there is some modeling deference between ground modeling software results and replicating same in robot

Re: How to model tension only springs with some pre-stress in robot?

Rafacascudo — Wed, 13 Mar 2024 11:11:42 GMT

More sofisticated modelling with more analysis options , or just the results are different?

Re: How to model tension only springs with some pre-stress in robot?

muhammad_hasan88NXQ — Wed, 13 Mar 2024 13:41:44 GMT

As you said since the geotechnical softwares are more sofisticated in modeling soil intraction that robot they are giving beter results. and since they cannot fully get the structural behaviour we are modelling the same in robot to get the structural behaviour. We are trying our best to match the robot results with plaxis (geotechnical model) behaviour.

Re: How to model tension only springs with some pre-stress in robot?

Simau — Wed, 13 Mar 2024 14:12:02 GMT

@muhammad_hasan88NXQ

Is this wall not built by phases?