接口/接触概率lem of non linear analysis of RC Slab Strengthened with FRP using ABAQUS 6.8-2, need help

Dear Abaqus Users,

I have modelled and analysed a simply supported RC Slab strengthened with FRP using ABAQUS 6.8-2. Plastic analysis with Concrete Damaged Plasticity has been chosen to simulate the behavior of the RC Slab loaded at the centre. However, I have difficulties about the constraints between the surface of FRP and surface of the RC Slab. Abaqus did not recognise "tie" element for this interface between these materials. A good comparison between this simulation and the experimental test result is expected. However, tie constraints made the analysis to be terminated.

Concrete Slab is reinforced with 8 number of 12mm diameter of steel in each direction which are embedded into the concrete slab. Grade of concrete is C40.

Type of elements used are as follows:

Concrete: Solid, homogeneous, C3D8R elements

Steel: Truss, T3D2 elements

FRP: Shell Homogeneous, S4R elements

Your kind assistance and guidance is very much appreciated

ELMI