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Hi everyone!

I am starting to using the STKO software (literally I started yesterday) and I have a question: I want to use the ASDConcrete3D with a Preset Concrete (4P) for the constitutives shapes in tension and compresion, but I am not sure if the value that I input for fracture energy is the original fracture energy (with N/mm units for example) or is the original fracture energy divided by the characteristic length of the finite elements (with N/mm2 units in this case)? I have this issue because in other materials -like DamageTC3D or the User-Defined preset- it is explicit the autoRegularization option.

Also, in the case that the value that I have to input is the "original" fracture energy (in N/mm units), the software automatically recognizes the characteristic lenght of the mesh in the model? How does it work?

Thanks in advance!

When you use the presets, the fracture energy is always assumed in F/L, thus the automatic regularization is ON by default.

If instead you choose "User-Defined", you define the stress-strain curve, thus the fracture energy is not directly inputted by the user, but it's the area under your user stress-strain curve. In this case STKO asks you if you want to do the auto-regularization, and if yes, you have to define the reference size of the specimen from which you obtained that stress-strain curve.

In both cases, OpenSees will recognize, for each element, the element characteristic length, and will do the regularization