Optimum design and analysis of load capacity of corrugated web beams

A large part of the structures designed by civil engineers needs large spans due to the usage requirements of the building. When designing large-span structures, they must be produced in safe and economical way. The safety and economy characteristics of the design is directly related to the weight-to-strength ratio of the material which is used in the design. Steel offers more suitable solutions compared to other building materials as it has high strength ratio corresponding to high unit weight. As known, there are many types of steel profiles in the market such as box section, circular section and I section profiles. Among them, I-section steel profiles are frequently used for large spans. I section steel profiles are selected from narrow and wide flange profile types according to the purpose of the design and the loads they will carry. As a result of the requirements in the structural industry, new profile types are still emerging. The height of the new generation steel beams designed for large spans with minimum cost, is upgraded by increasing the moment of inertia and thus increasing the maximum load carrying capacity of the beams. However, as the height of the beam being increased, the web of the beam is simultaneously to be slender and this leads to web buckling and consequently sudden collapses. The corrugated wen beams designed to be developed by combining a thincorrugated steel plate with two steel plates and with same material properties, serving as the upper and lower flange, increases the load carrying capacity of the beam against shear force and local buckling while not only preventing the loss of stability and large deformations, but also preventing the rigidity loss of the beam before reaching the plastic limit under applied loading combinations . With this special structure of the web of the beam, the economic gain is achieved by decreasing the beam self-weight and increasing the load carrying capacity. In the scope of this thesis, firstly, the dimensions of the corrugated web of beams is designed by using optimization methods with minimum weight. For this purpose, the web height, thickness and the distance between the peak points of the corrugated web as well as the flange width and thickness are considered as design variables. The values of these design variables causing the minimum beam weight are obtained under behaviour and geometric constraints. The solutions of the structural optimization problems formulated have been obtained by adaptation of two recent optimization techniques that are hunting search and firefly algorithm methods and the performances of these two methods in the process of finding the minimum weight are compared. In the experimental process, which is the second and main stage of the thesis, the optimally designed corrugated beams are tested under single loading, two points bending and the distributed loading by using the loading frame with pressure cylinder which has hydraulic power unit. After the steel beam tests made on the structural element basis, the maximum load carrying capacities are calculated by examining the behaviors of the corrugated web beams under the load acting on the composite designed slabs. In the last part of the thesis, the web plate buckling analysis of the steel beam specimens with corrugated webs and the calculation of the critical loads that they can carry are executed by using the finite elements software and the results of the finite elements analysis for the corrugated beams with different web thicknesses and lengths are compared with the results obtained from the experiments. Design limitations for corrugated web beams have been taken from BS EN1993-1:2005 (Annex-D, Eurocode 3) and DIN 18-800 Teil-1. Additional limitations adopted from BS-8110 have been considered for the composite systems.