Hello Everyone.
I am working on a design of monopiles under cyclic loading condition.
I am using UDCAM-S model. It is clearly mentioned that this model can be used in offshore structures that experience storm loadings.
I am aware that using this model, there will be decrease in the effective stress due to pore pressure accumulation.
In my understanding, in addition to use this model, I have to apply the cyclic load at the top of monopile above the ground level.
I believe that that cyclic load should be applied in dynamic step.
However, it is mentioned in Material Model Manual that UDCAM-S model should not be used in dynamic calculations.
I am confused whether I am understanding it right? Please correct me if I am wrong or provide the clarification regarding this.
Thank you.
Dear Bilal,
The UDCAM-S model should indeed not be used in a dynamics analysis. What the UDCAM-S model does is first determine the reduced strength and stiffness due to cyclic loading (using the cyclic accumulation tool) and then perform a STATIC analysis using reduced parameters. Hence, the UDCAM-S model is not to model the cyclic loading itself, but to take into account the reduced parameters in a static analysis.
See also Tutorial 10 of the PLAXIS 2D 2023 Tutorial Manual.
With kind regards,
Dennis Waterman
Answer Verified By: bilal adeel
Dear Mr. Dennis,
Thank you for providing the clarification. That means the static load will be applied on the top of monopile in terms of prescribed load or displacement and soil strength and stiffness is reduced depicting the cyclic load accumulation procedure. In continuance to that, UDCAM-S model as mentioned in the manual that it is only for undrained condition and mostly suitable for clays.
However for sands, if they experience cyclic loading, which constitutive model is suitable to use that can accomodate reduced strength and stiffness due to cyclic load ?
Thankyou and regards,
Muhammad Bilal Adeel.
In principle any model suitable for sand is suitable for cyclic loading as long as the user specifies the reduced strength and stiffness. In principle the UDCAM-S model also requires reduced parameters as input, but what the UDCAM-S model offers as an extra is that with the cyclic accumulation tool it can determine the rate of reduction with number of cycles. But the residual values are user input.
Hence, for any other model you can fill in reduced parameters, but you would have to determine them yourself and then apply the static load as in UDCAM-S.
PLAXIS does not have a model that can actually model the process of strength/stiffness reduction with multiple load cycles.
Dear Mr Dennis,
Thankyou for the answer. I have one confusion. When you are referring to residual values are user input valuses you mean the default curves (Contour diagram data) present in UDCAM model in cyclic accumulation and optimisation tool i.e. Drammen Clay with OCE 1,2,3 and so on, ? Is that right? please find attached picture for clarity.
Now If the user can input those curves manually for sands, the model can work for sands as well? Did I understand that correctly?
With residual strength I mean the cyclic shear strength, which in this case is the final value of the curves you show.I agree that you could decide to simply use curves for sand if you have them. However, UDCAM-S
- uses undrained shear strength, so you would need undrained shear strength data for sand- is tailored for clays, it uses for instance a yield surface with associated flow.
So you may put in the correct cyclic shear strength, but to what degree for instance the deformations would be correct for a sand is hard to say since the model was not made for sands.