In steel structures, a lot of attention is paid to lightweight structure, i.e. reduction of dead load without compromising structural safety, integrity and performance as well as cost-effectiveness. Thanks to modern steel aluminium sandwich panel manufacturing technology a new possibility became available for lightweight structural design.The objective of this thesis is to evaluate the application of sandwich panels in the construction of steel structures with the aim of weight reduction without affecting other parameters like safety, performance, cost, etc. In this thesis, both column and plate buckling theories are considered and applied to the sandwich panel to evaluate its behaviour under in-plane compressive load. Effects of various material models and imperfections on buckling strength of sandwich panel are evaluated. Stiffened plate and sandwich panel is compared in terms of buckling resistance and self-weight. Three different sandwich panels made from faceplates of steel grade, S355, S690 & S1100, are used for replacement of S355 stiffened plate. Efforts made to understand the effect of various physical parameters on buckling resistance of sandwich panel in both column and plate buckling theories.Finally, as a case study, sandwich panel technology is used to redesign the Huisman structure. The objective is to investigate whether applying sandwich panels in redesign makes it possible to obtain a sufficient weight reduction without losing its performance. For this case study, sandwich panels with faceplates of steel grade S355, S690 and S1100 are used. Static and buckling strength of the new design is evaluated. Also, the cost of new design and original design is evaluated and results are compared. Cost analysis is done to evaluate whether a sandwich panel is an economical solution.Findings of this thesis are that in future it is possible to use sandwich panels in offshore structures to save a significant amount of weight while taking considerations into account. Sandwich panels can be successfully used to replace stiffened plates. Sandwich panels with faceplates made from extra high strength steel can give significant weight reduction. But the use of sandwich panels also results in an increase in the overall cost of the structure. So in terms of costs, it is questioned whether or not using sandwich panels is economically beneficial for offshore equipment.