Errors in Pressure Independent Multi Yield Material

[rafetsisman]

Hi,

I have read from this forum that the documentation of PressureIndependMultiYield material includes some mistakes and contradictions. Thus, I looked into the source code to correct the documentation and I realized that;

when phi (friction angle)>0 shear strength (for deriving yield surfaces) is calculated as:

tauF=cohesion+2*sqrt(2)*sin(phi)*refPress/(3-sin(phi))

and when phi=0 shear strength is calculated as:

tauF=2*sqrt(2)*cohesion/3

However, in case of non-zero confining pressure, these formulas become invalid. And it seems that OpenSees calculates smaller shear strength values by using (5/9) of the intended confining pressure. By the way I incorporated confining pressure to the quad elements directly.

How can I get correct shear strength values? What are the correct equations for shear strength?

Thanks,

Rafet