topic Re: Tunnel model - spring supports in Robot Structural Analysis Forum

Tunnel model - spring supports

dp1 — Sun, 08 Jan 2023 13:09:43 GMT

I am trying to model the secondary lining of a tunnel. I want to model the ground as springs (similar to beam spring model). However, when I try to apply a spring as a support I don't know which direction to fix it in. Also, I want the springs to point at the centre of the tunnel, but when I specify this in the "direction" dialogue, it does not work.

Can someone help me with where I'm going wrong? I have attached the file.

Re: Tunnel model - spring supports

dp1 — Sun, 08 Jan 2023 14:38:51 GMT

I have sort of figured the question out, but how can I go about adding radial compression? My results are way off the example I have.

Re: Tunnel model - spring supports

Rafacascudo — Sun, 08 Jan 2023 14:42:02 GMT

Well , I couldn´t find the assigned thickness TH280 on the thickness dialog window. Creste it again assign it to your tunnel panel and on this thickness dialog ,mark "Parameters of foundation elasticity" and enter the soil spring values. They will be always perpendicular to the panel surface

Re: Tunnel model - spring supports

dp1 — Sun, 08 Jan 2023 20:08:50 GMT

@Rafacascudo thanks for responding. I have now done this and attached the model again. I still get some funny shapes for the results, when I'm looking for something more like (not exactly) the following:

What do you think?

Re: Tunnel model - spring supports

Rafacascudo — Mon, 09 Jan 2023 17:27:26 GMT

model you sent seems to be the same as before with no material , no support and no thickness assigned to the tunnel panel. So I create a new thickness named ESP280_C30 , with 280mm thickness and material concrete C30 . For elasticity parameters I used kz=10 kN/m3 and Kx=Ky=1kN/m3 , with uplift Uz- as the soil can only give support in only one direction . As your panel has Local axis Z pointing outwards , direction Z-(radial towards circle center) is free to translate.

With that , analysis becomes nonlinear(support with uplift) and model runs without errors.

For dead weight load case I get the following results

Soil reactions

Moments

Model attached

Re: Tunnel model - spring supports

dp1 — Mon, 09 Jan 2023 20:41:07 GMT

@Rafacascudo thank you so much for sending that through - first time I've seen some realistic results!

But I think I have messed it up again. Can you please help me understand what the elasticity parameters are relating to? The tunnel I am modelling is in "London Clay" (silty clay) which is 50m deep in the ground with a shell of unreinforced concrete around it. Therefore the stiffness of the surround of the tunnel is related really to the concrete. I am looking to use these values.

Radial nodal stiffness = 218,276

Tangential nodal stiffness = 30 kN/m/m

I am not sure what the elasticity parameters are relating to so I can't input the appropriate values?

Re: Tunnel model - spring supports

Rafacascudo — Mon, 09 Jan 2023 23:26:23 GMT

By that table ,you have spring values for your mesh nodes. So it depends on the distance between them/RSA mesh size.

In RSA the input is an area spring which is transformed to nodal spring internally.

Best you can do is ask your soil engineer which spring values to input in RSA.

Re: Tunnel model - spring supports

dp1 — Tue, 10 Jan 2023 11:09:35 GMT

@Rafacascudo thanks for the help. I think I'm close to getting it to work.