Large deformation structural performance of double skin composite construction using British Steel's 'Bi-Steel'
Double skin composite construction consists of two relatively thin steel plates with the space between filled with, usually, normal weight concrete. The transfer of shear between the steel and concrete is possible through the use of steel shear connectors that are welded to the steel plates. A study of previously published information revealed that the areas to market double skin composite construction would be submerged tube tunneling and floating offshore structures, particularly those used for the storage of crude oil. Double skin composite construction was traditionally fabricated with headed studs, as used in composite bridge construction. These were welded to each of the steel plates which were then temporarily held in place whilst the concrete was cast. This method of construction was costly in time and labour so British Steel PIc and The Steel Construction Institute developed an idea of using continuous friction welded bars. These connect to both plates to form a continuous steel structure. By manufacturing steel panels, up to 12m by 3m in a factory environment that requires no additional formwork allows great savings in time and labour during the construction process. Research on Bi-Steel, as it is known, is being carried out on numerous fronts with that detailed in this thesis being part of it. This thesis covers the overall performance aspects of strength and stiffness throughout the elastic and plastic regions of deformation and includes local buckling of the compression plate. Analytical solutions are developed for all aspects dealt with by this thesis which are supported with an experimental test programme. The test programme uses 16 full-scale, wide beam specimens that are tested in three point bending. The first series of tests carried out, which used the first two prototype Bi-Steel panels, compared the existing method of construction of double skin composites with Bi-Steel, the new method of construction. The second series of tests, divided into two parts, helped to develop the strength, stiffness and local buckling equations. The first series of tests showed that Bi-Steel was structurally the better performer. This was due to the continuous nature of the steelwork, which allowed the full strength of the steel to be achieved and structural continuity even after buckling failure. The traditional method of constructing DSC was no weaker or less stiff than its Bi-Steel counterpart, but the headed shear studs prematurely pulled out of the concrete. The second test series, which only used Bi-Steel panels, showed that an Euler analysis can be carried out to determine the buckling load of the compression plate. It also showed that the post yield gain in strength of the panels was due to strain hardening of the steel tension plate. In conclusion, it has been structurally and financially beneficial to develop Bi-Steel. The factory fabrication of the steelwork increases quality control and the unit type product allows easy on-site assembly. The structural performance of Bi-Steel is now well understood with few areas left to study which are now being addressed. The first design code has now been produced by SCI for the design of Bi-Steel components.