Optimization of diagonal stiffeners to handle wind pressures on silos

Sammanfattning: In this report the focus is set on how to optimize the support structure of a silo and in particular, the stiffeners and fastener. The main force of the silo comes from the wind pressures. The design is subjected to the Swedish and European standards SS-EN 199-1-4:2005, 1993-1-1:2005 and 1990. Much of the design work was put on determining the pressure for buckling of the stiffener and to determine the shear force on the bolts. Calculations on how the silo was affected by wind pressure was also calculated by the use of the SS-EN standard. The silo that is analyzed started with a design that was largely conservative designed, which is making it hard for the company constructing the silo to compete on the European market. The focus of the report is to minimize the material needed for the diagonal stiffeners between the columns. This because the diagonal stiffeners made up 80\% of the total stiffener length. The idea is to change the U-shaped beams with the dimensions 50x30x2 to L-shaped beams with the dimensions 25x25x2. A plate that earlier connected the stiffeners was removed and replaced with a circular plate that were put at the place where the diagonal stiffeners intersected each other. This was possible since the stiffeners were put in a configuration where they would not hit each other but instead go past one another. The new ring was placed in the gap between the stiffener. The simulation in Abaqus was performed with the following wind pressures:\\1. Roof: 0,78 MPa.\\2. Shell: 0,5 MPa.\\3. Columns: 0,8 MPa.\\The allowed limiting pressures on the stiffener based on the wind pressures were:\\1. Allowed pressure around bolt: 692 MPa.\\2. Allowed pressure to prevent buckling: 183 MPa.\\3. Allowed pulling pressure on stiffener: 273,6 MPa. \\By color scale it could be determined that the silo would remain stable. The areas that exceeded the allowed values in Abaqus were considered singularities and could be neglected. From a manufacturing point of view, the proposed change was possible if two machine tools were used. One for the original stiffeners and one for the changed diagonal stiffener. All changes follows the European standard and resulted in a 24\% cost reduction when counting in the cost of all the stiffeners. The optimized diagonal L-shaped stiffeners has resulted in a decrease in price by 36,3\% while the unchanged stiffeners have increased in price by 26,1\% due to the adding of an additional machine.