An analytical model was developed for the mechanical behavior in joint surface of composite structures, which consist of steel plates and concrete. Steel plates were idealized into shell elements and assumed to behave as the elastoperfectly plastic models. Concrete was idealized into solid elements and assumed to behave as the elastoplastic model in which the hardening and softening behavior of concrete can be estimated due to the 2 parameters model of Drucker-Prager type yield surface. In the joint surface, using Lagrange undecided multiplier method in which the continuity of displacement can be taken into account and the joint elements in which the slip can be taken into account, the modeling of virtual elements was constructed.
Due to the comparison between the experimental and analytical results for the mortarfilled steel tubular columns under uniaxial compression, the analytical results show a good agreement with experimental results and it should be noted that the applicability of the proposed model was confirmed.