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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 57658 (09)
- University: Sharif University of Technology
- Department: Civil Engineering
- Advisor(s): moazezi mehr Tehran, Alireza
- Abstract:
- Cylindrical steel shells are common industrial structures. Due to their thin thickness, these structures are very susceptible to buckling under applied loads. For access and repair purposes, cutouts of various shapes and dimensions are used in these structures. The presence of such cutouts increases the sensitivity of these structures to buckling; therefore, it is necessary to use stiffeners with different dimensions and shapes around the opening to restore the lost capacity. Cylindrical shells are designed in different lengths for use in different structures. The most common shapes of these structures are silos, tanks, and turbines. Due to the effect of the slenderness of these structures on the buckling strength, these structures are classified according to their length. Among the different length categories introduced in EN 1993-1-6, medium-length cylindrical shells are more common among shell structures. There are few studies on the simultaneous effects of the presence of a cutout with different dimensions and boundary conditions on the buckling strength of these structures. Therefore, this research presents a numerical study on the capacity of medium-length shells with opening and stiffeners under the effect of axial and bending loads. Axial load is caused by the weight of the structure itself, the weight of structural equipment such as ventilation systems, and the weight of the materials contained within the shells. Additionally, bending loads result from the forces generated by seismic activity, wind, or the presence of a cutout. The numerical finite element analysis conducted in this research is in accordance with the provisions of the European regulation, which is a well-known and advanced international standard for the analysis and design of shell structures. In this study, numerical modeling was conducted using the Abaqus software. A total of 486 models were investigated using Abaqus/Standard. Different shell dimensions, boundary conditions at the top edge, and shells with or without of the stiffeners are studied on the modeled shells. Additionally, the models have a cutout of varying sizes, either square or circular, and were subjected to axial compression. The results demonstrated that the presence of the cutout resulted in a pronounced reduction in buckling strength, reaching up to 61%. This decline in capacity was particularly pronounced in shells with rotational freedom at the top edge, where it reached a maximum of 30%. Furthermore, it was observed that the use of stiffeners can effectively restore the lost strength. In order to predict the strength of the shells with cutouts and without stiffeners, a series of equations have been proposed. The accuracy of the fitted equations was investigated in a separate study, in which the silos of one of the researchers available in the technical literature were examined. In this manner, cutouts were positioned at five distinct levels within the silos of the aforementioned study, and the ultimate strength of these structures was then compared with the fitted equations. The results of the numerical analysis and the formula exhibited a high degree of correlation. In conclusion, 360 finite element models were constructed to investigate the behaviour of shells with circular openings subjected to a combination of compressive and bending forces. The results demonstrate that the presence of openings has a significant impact on the strength and behavior of these structures when subjected to compression, pure bending, or a combination of these two types of loading. In order to quantify the results of the aforementioned 360 runs, some equations were derived using regression methods
- Keywords:
- Cylindrical Shells ; Boundary Conditions ; Stiffener ; Axial Load ; Bending Moment ; Opening ; Buckling
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