Instabilidade global de silos cilíndricos metálicos com chapas corrugadas enrijecidas verticalmente.

Abstract

In the design of cylindrical metal silos, the verification of global instability resistance is one of the most important steps in the project; therefore, neglecting this verification can make the structure susceptible to structural failures. The global instability of metal cylindrical silos with vertically stiffened corrugated sheets is still less studied compared to other shell structures. The critical elastic buckling load in orthotropic stiffened shells is fundamental for assessing their resistance to instability. The standard EN 1993-4-1:2007:A1(2017) recommends two calculation methods: the Donnell Mushtari-Vlasov orthotropic shell approach and the elastic base column theory. Research on the application of the models prescribed by the Eurocode has indicated that the results obtained from these methods tend to be conservative in determining the critical buckling load. The objective of this work is to analyze the methods used to perform global stability analyses of metal cylindrical silos with corrugated and vertically stiffened sheets in order to validate the analytical and numerical methods, and to propose recommendations that assist in the design of silo supports. Three case studies were conducted. The initial analyses covered silo models with diameters of 4.55 m, 10.0 m, and 14.55 m, all with a height of 20.0 m and a spacing of 1.429 m between supports. For each diameter, four thicknesses (0.95, 1.55, 2.25, and 3.0 mm), two corrugation profiles (101.6x11.1 mm and 76x18 mm), and two support sections were evaluated. The linear stability analyses – LBA were performed using finite element software SCIA Engineer. Additionally, a real silo model with a diameter of 5.35 m, belonging to a group of silos built in Poland, was analyzed using the analytical and numerical methods studied in this work. Finally, the silo model experimentally tested by Rodrigues (2019) was modeled using the finite element method. For this, two distinct models were constructed: in the first, both the corrugation of the sheets and the supports were represented by shell elements with isotropic behavior; in the second, the corrugated sheet was modeled with orthotropic shell elements, while the supports were represented by bar elements. The calculation of the resistance to instability of the supports of this silo was performed using the methods from the Brazilian standard NBR 14.762:2010 and the European standard EN 1993-4-1:2007:A1(2017). In the analyses of the silo models, the results showed that the most accurate method for the diameter of 4.55 m was method b), while for silos with diameters of 10.0 and 14.55 m, it was the Sanders method. The analyses conducted for the real silo model SL535 demonstrated that the load factors calculated using method (a) produced results closer to those found in finite elements. The simulations of the silo models studied by Rodrigues (2019) indicated that the orthotropic shell models produced accurate results when compared to the 3D model. Furthermore, it was verified that the position of the wind rings did not have a significant influence on the increase of load factors. In calculating instability resistance, the European standard method presented greater accuracy compared to the Brazilian standard method.