Issue with Soil Pressure Display in Robot Structural Analysis

[hlynurKTA5E]

I'm encountering a discrepancy in Robot Structural Analysis where the moments calculated for a retaining wall are correct, but the displayed soil pressure is wrong.

Details:

• Soil parameters: Friction angle 38°, soil weight 19 kN/m³, wall height 3m.
• Expected pmax (Ka): 13.5 kPa with a corresponding moment of 20 kNm/m.
• Robot shows: pmax as 27.12 kPa but calculates the correct moment of 20 kNm/m.

When I manually applied a linear surface load of 27.12 kN/m, the moment calculated was 40 kNm/m, as expected.

It seems Robot calculates the correct pressure behind the scenes but displays double the actual value. Has anyone else encountered this issue? Is this a bug, or am I missing something?

The attached screenshot illustrates the issue:

• Left side: The wall where Robot correctly calculated the soil pressure and moment but displayed the wrong pressure value.
• Right side: A wall that appears to have the same load as displayed on the left but results in double the moment (40 kNm/m). This clearly shows a conflict between the displayed load and the actual calculations

[Rafacascudo]

can you please zip and attach the model?

[Simau]

Hi @hlynurKTA5E 

It's not an issue.

When you define soil pressure for a certain height robot give you pressure for the double, so all wall in that interval are loaded.

 Test model attached

[hlynurKTA5E]

Hi @Simau,

Thank you for your reply.

I appreciate your input, but I'm still having trouble understanding your explanation.

I may not have been clear in my initial description. The two walls in question are side-by-side, both at the same elevation (0-3m) with "medium gravel" soil from 3m elevation.

If you understood that my walls were at the same elevation, then I do not understand how your example applies to mine. I understand that soil pressure is defined in the global coordinate system, which could explain different loads on walls at different elevations. However, in my case, the load transitions from 0 at the top to 27.12 at the bottom, not 13.56 at the top and 27.12 at the bottom, which would make sense if the wall was at a 3-6 meter depth. What I should see is 0 at the top and 13.56 at the bottom.

From my perspective, the linear increase in pressure with depth seems to be displayed as twice the expected value. Since soil pressure is calculated using p(h)=K⋅γ⋅h, it appears that either the K value or soil weight γ is being displayed (but not calculated) as double the correct value.

Could you clarify what you mean by Robot "giving double the pressure so all of the walls in that interval are loaded?"

Even if there's a misunderstanding on my part, I still believe this is an issue. Would you agree that the image I attached in the OP shows a contradiction? The same load on the same wall is giving different moments, which doesn't seem right.

Thank you for your assistance.

[Simau]

Hi @hlynurKTA5E 

Sorry for my bad explanation.
Please take a look at this example, and if it's still not clear, please share your file

Displayed pressure is at z=3.00

Bending moment is ok (for 13.30 pressure)

Model attached