Ad 2.: What elastic tube :-) ? If you mean the elastic cube, about the size of the finite elements in the concrete usually works well.

1- yes FRP bonded to concrete , already i have defined the interface. How to make the master slave connection at the end plz ?

2- yes the dimensions of the elastic tube holding free end and

Ad 1.: If I understand correctly that you have some FRP layer bonded to a concrete surface + anchored at its ends, the simplest model would be to have Interface elements representing the bond + Master-Slave connection at the ends, connecting the surface or edge of the laminate to the concrete.

Ad 2.: You mean the dimensions of the elastic cube, holding the free end of a bar/cable when modelling a pull-out test (Troubleshooting, 2.2.12 How can I model a pull-out experiment?)?

Or are you asking how to design the anchoring region of a prestressing cable?

Regards.

1- I am asking about how to model anchorage system for prestressed FRP laminates, the laminates are anchored from it's beginning and end, how to represent that the laminate is held from it's ends.

2- The concrete block used in prestressing at the start and end points of the cable, what is the most reasonable thickness for this block ?
Is there any relation between its thickness and transfer of prestressing force, load value, behavior of the member.

Thank you for your care and help