I have my shear wall Mat foundations modeled with an area spring below. But I still get the error for large deflections. When looking at the gravity load combos the deflections are reasonable. Is there a way to see the lateral deflection? What deflection does RAM consider to be large? I have increase the slabs and dead load on top of the footings and still the error.
Probably sliding. See: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/3038/ram-instability-in-finite-element-analysis-tn#mat
Would it be reasonable to leave this error or increase the soil constant in the R and S directions and check sliding by hand calculation? Or is there away to apply a soil friction factor to Concepts? I have a friction factor of 0.4.
If the problem is sliding and you don't care about sliding I suppose you could ignore it, but I always prefer to keep the model from moving so much. I usually use R and S coefficients. These horizonal spring stiffness values are not exactly the same as friction factor (mu), but if you know the total weight and area (which you can get from the calc log and estimate) then you should be able to come up with reasonable R and S values to use. Edge restraints are another good option.