Please note that reduction of stiffness does not lead to any change in stress or strain. Therefore, the behavior of structure would not be changed just by stiffness reduction of the section.
Hi, i feel you have to obtain the backfill soil parameters for the design of wall by conducting consolidated drained test results. For long term stability check for retaining wall the backfill materials properties to be obtained by conducting consolidated drained triaxial test results..the results obtained from this test can be used for the analysis and design of a retaining wall..ok all the best..
To investigate the earth pressure against the retaining wall a model in PLAXIS can be formed using both Mohr-Coulomb theory and the Hardening Soil model to investigate the behavior of the soil. The primary focus may be to model the soil as a material with the properties as prescribed by Mohr-Coulomb theory. The rules in Bro 2004 can be used for modeling the temperature change. The results from the model should not differ much from the calculations according to Bro 2004, but the requirements in Bro 2004 are usually too pessimistic in some cases. The demands in the Eurocode are even more pessimistic but also more difficult to analyze since the demands aren’t that clear. One advantage is that the behavior of the soil can be studied since PLAXIS may show the results in many ways such as patterns for displacements, moment and force distributions, the stresses in the soil, points for plasticity etc.
All the best.
I think if you could use the PLAXIS version 2018 because this version was implemented with a new constitutive model of concrete material simulating time-dependent strength and stiffness of concrete, strain hardening-softening in compression and tension as well as creep and shrinkage. More details about this model are available in PLAXIS 2018 material manual
In the formulation of fem or mdf, if the model is equilibrated no effects is visible if the stiffness is changed with elastic based constitutive model (i'm not speaking on plasticity failure criteria)
Please refer to
https://www.plaxis.com/support/tips-and-tricks/stress-relaxation-due-creep-concrete-structures/
where you can find the "official" methods to do that.
Bye
Luca
Thanks everyone for your contribution to this question.
I have also had a bit of research and communicated with Plaxis support team. They have also admitted that if a plate element has been used to model the retaining structure, the long-term behavior cannot be modelled just by reducing the Young’s modulus (E) value. You can see more explanations through the link below.
https://www.plaxis.com/support/tips-and-tricks/stress-relaxation-due-creep-concrete-structures/
However, as Luca mentioned it is possible to model the stress relaxation due to creep in concrete structures using a combination of a solid element and a plate element. Please check the following link for more details about this approach.
https://www.plaxis.com/support/tips-and-tricks/stress-relaxation-due-creep-concrete-structures/
It should be noted that modelling the retaining structure as solid element when we are dealing with complex model has following disadvantages:
1- The calculation stage would take ages to be completed
2- The size of the model would be very large
3- It is very challenging to model the structure as solid element when the geometry is complex
4- Extracting structural actions of a retaining structure modelled as solid element is not straight forward
It seems that still a more practical approach is needed to model the long-term behavior of a retaining structure efficiently.
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