Oppsveiset rammehjørne av stål i flytende offshoreinnretninger : Kapasitet og spenningskonsentrasjoner

Abstract

In this master thesis we study a corner detail between a deck and bulkhead plate, located inside a semi submersible platform. The platform structure is made from steel components such as plates, stiffeners, girders, and brackets. The deck is supported by paralel beams which ae supported on columns that are connected to the bulkhead. The corner detail, where the beam comes across the column, is often exposed to high stresses that can be critical for both the capacity and fatigue life of the structure. A common way of improving this detail is by using brackets, stiffeners and thicker plates. The intention of the thesis is to analyse different shapes of the corner detail, and to determine which one has the largest capacity and best fatigue resistance. Due to the complex geometry of the corner detail, analytical solutions are difficult to find and it is convenient to apply finite element method to obtain the results. Linear elastic theory is used to determine the stress concentration factor and estimate the fatigue life of the structure, for the different types of load cases. A buckling analysis is utilized to determine the first five eigen values, which are further used to introduce an initial shape deflection in the non linear analysis. Three different models of the corner detail, based on Aker Solutions standard details, are created and analyzed. For each detail, different boundary conditions and load cases are applied, in the finite element method software Abaqus. The best model is determined by comparing the results from both the linear and non linear analysis, for every load case, for all three models. Results from the non linear analysis are also compared with hand calculations, in cases where this is possible, while results from the linear analysis are verified by comparison with results for similar details found in literature. Based on the results from these three models, a modification of the corner detail is presented and analyzed in Abaqus with the same boundary conditions and load cases as earlier. The main intention of the modification is to improve the capacity of the detail. The final analysis results are compared with the former three models.