Hi,

First: What I'm trying to do

I am modeling shear bond strength between old and new concrete. This means i have a contact surface between the substrate (old) and overlay (new) concrete. to test this i am basically creating a cube (150mm3) with two halves of different strength concrete and shearing them at the interface.

now...

in Atena, i am modeling this with a GAP material between the two surfaces. at this stage i am still playing around with the cohesion and friction factors to see their direct influence while keeping tensile constant. Am I correct in assuming that:

i) the Gap material is not a "filler" or "physical" material but  rather description parameters for the behavior and surface properties of the contact between the surfaces ?

This would imply that:
- Cohesion is actually adhesion between the contact planes and
- friction would indicate a mechanical friction coefficient between the planes
- the tensile strength is an indication of the pull-off bond strength capacity of the two surfaces. would cohesion and tensile strength not be the same then or do is the assumption for cohesion wrong?

ii) Would the Tangential and Normal Stiffness coefficients be the Stress / displacement slope up to failure ? you would calculate this by normal (or tangential) force / area / displacement to failure ?

iii) the min Ktt and Knn values used for computing be the failure slope (i.e. -> surface failed in normal or tangent when this value is reached and Ktt min is always less than Ktt (same for Knn)) ?

also, where can i get more info on the theory behind the gap material parameters ?

Thanks