Mesh independent modelling

[leartt]

Hello,
I have a question regarding the concrete regularization techniques that are used in STKO. If for any reason, we do not wish to use the ASDConcrete material that utilizes auto-regularization, but wish to use the conventional concrete materials like Concrete01, which empirical expression does STKO use for computing the compressive fracture energy of concrete Gf,c? In one of your recent webinars, Mr. Petracca mentioned the expression from Model Code (0.073*fc^0.18), but that one is used for computing the tensile fracture energy. How does it compute the compressive fracture energy for unconfined but also for confined concrete? My last question is: If i wouldnt prefer to use empirical expressions for Gf,c, can i use the calculated value of Gf by computing the post-peak area of the stress-strain curve that can be mathematically explained by one of the famous concrete models that are described in EC8-2; EC8-3?
Kind regards,
Leart Taravari

[STKO Team]

0.073*fc^0.18

This one is used for the tensile fracture energy. NOTE: it assumes fc in MPa, and gives the Gf in N/mm. so pay attention to the units (stko does conversions internally)

compressive fracture energy of concrete Gf,c?

Gc = 250*Gt

for unconfined but also for confined concrete?

That is unconfined. The 3D concrete model naturally captures triaxial effects and confinement. For 1D cases, you can to provide your own fracture energies

f i wouldnt prefer to use empirical expressions for Gf,c, can i use the calculated value of Gf by computing the post-peak area of the stress-strain curve that can be mathematically explained by one of the famous concrete models that are described in EC8-2; EC8-3?

If you want to provide custom fracture energies, choose the Preset with 4 or more parameters to have control over the default Gt and Gc. But pay attention: There you have to provide the real fracture energies, i.e. the area under the stress-displacement curve. If your experimental references gives you the specific fracture energies (i.e. the area under the stress-strain curves) you have to multiply them by the reference (specimen) size!