The authors have been developed a new composite steel-concrete material for the strength members of huge offshore structures both in harsh or Arctic environment. where concrete is placed between steel plates. Discussed in this paper are experimental and theoretical investigations into the elasticplastic behavior and the ultimate strength of the new composite material. Experiments under static and repeated loadings were carried out. Five types of test models of composite materials were subjected to shear. The following information was obtained (I)T-stiffners and long stud bolts which were employed to connect steel plates and concrete. were quite effective to increase the ultimate strength and amount of deformation and could absorb a great deal of energy at failure. (2) The effect of repeated loading on the strength and rigidity of the composite was clarified. (3) The comparison of the calculated results with the measured ones showed good agreement.
Recently various kinds of conceptual designs of Arctic offshore structures have been proposed. In designing such structures designers have to pay particular attention as to how to overcome ice loads acting on the structures. The use of a composite steel-concrete sandwich system appears to be viable solution for offshore structures in the Arctic. The authors have developed a new composite steel-concrete sandwich system structure to cover up the various drawbacks of both the concrete and the steel.  The new composite system endures large deformation and absorb a great deal of energy at failure because the steel plate with high strength and ductility suppresses the development of surface cracks. In the paper the authors carried out investigation into the strength of the composite material. where concrete was placed between steel plate. Stiffeners were also furnished to increase the buckling strength of the plate. The steel plates were connected with web plates.