The characteristics of the interface bearing strength for the concrete filled GFRP box sections was studied conducting the experimental push-out tests. Hallow pultruded 125 mm long square GFRP box sleeves were cut from the pultruded GFRP sections, and naturally bonded, epoxy bonded, granular aggregate bonded surface treatments and mechanical connections were implemented on the specimens before concrete placement. The experimental results showed that the initial fracture strength of the naturally bonded specimen was increased from 0.28 MPa to 1.36 MPa with the epoxy bonded surface treatment. On the other hand, granular aggregate bonding surface treatment provided full composite action resulting confinement rupture of the GFRP boxes. Proper surface preparation allowed to distribute interface shear stresses while increasing the bearing capacity and did not cause localized bearing stresses as observed with presence of mechanical holes. Finally, confined cohesive zone material model (CCZM) was proposed and implemented in finite element models.