Offshore structure should have a high degree of structural safety even under extreme environmental load conditions. The authors have suggested an importance of use of composite steel concrete structure of sandwich system for the strength members of huge offshore structures. In the previous papers, the authors carried out both experimental and theoretical investigations on the toughness of the sandwich composite structures. Experiments were carried for the two dimentional models of composite structures under pure bending and combined shear and bending as well. A nonlinear analysis was made to predict the toughness of sandwich beam under pure bending. In the present paper, the authors have carried out model tests under shear and have developed a nonlinear analysis method to predict the toughness of sandwich beam under shear and combined shear and bending. In the nonlinear analysis the material nonlinearities of both concrete and steel plate have been taken into consideration. The results of nonlinear ultimate deformation analysis have been found to be very close to the test results.