Simple shear test under constant amplitude CSR condition

[Lanka]

Hi forum,

I'm trying to calibrate model parameters (PT angle, contrac, dilation and liquefaction parameters) of PDMY material using single element simulation (using quad-UP element). Basic purpose of this calibration is to get reasonable post-liquefaction shear strain (in saturated loose sand, relative density less than 35%) at the end of earthquake shaking.

For this, I want to mimic a simple shear test which maintains constant-amplitude CSR (cyclic stress ratio) throughout the test. To maintain constant-amplitude CSR, I want to apply horizontal velocity to top nodes until shear stress reaches a limiting value which corresponding to the value calculated from amplitude of CSR (for example, if the amplitude of CSR is 0.1, the limiting shear stress is 0.1*initial effective vertical stress); Once the shear stress reaches the limiting value, I want to switch the sign of velocity command (i.e, to move in opposite direction) until shear stress reaches limiting value in the opposite direction (-0.1*ini. effect. vertical stress). The above steps will be repeated for many cycles until soil developes very large post-liquefaction shear strain.

Have anyone tried similar procedure before in OpenSees? Is there way to switch the sign of velocity command during the analyses by checking shear stress with the limiting shear stress (i.e., to switch the sign of velocity when shear stress=(+/-)CSR*ini.effec.vertical stress). Is it possible to make a test on shear stress during OpenSees analyses (this can be done in FLAC, I'm not sure about this capability in OpenSees)


Or anyone knows other better procedure to calibrate PDMY material parameters for post-liquefaction response? I'd appreciate any help on this.

Thanks.

[majid-OS]

Hi,

I am trying to model the same problem.
How did you model a simple shear test?
Where and how did you applied the motion?

Thanks,
Majid

[bieszczady]

Hey - I have got too that same - somone know hov to fix that ?