Okhten I. Stability of an thin-walled open-profile bars with imperfections of form

The dissertation work is dedicated to the investigation of the stability of thin-walled open-profile elastic bars with imperfections of form. A numerical methodology for researching the stability of bars with geometric imperfections of various amplitudes and forms has been developed based on the finite element method and computational procedures of the NASTRAN software complex. It has been devised an algorithm for computer finite element modeling of thin-walled bars in the form of a set of planar shell elements. Software has been developed for modeling geometric imperfections of various amplitudes in the form of local and global shapes of stability loss for bars, considering the out-of-plane deformation of their cross-section which adapted to the NASTRAN computational complex. The effectiveness of modeling thin-walled bars in the form of a set of shell finite elements has been confirmed by solving a test problem of the stability of beams of a trading complex in Mykolaiv, considering various scenarios of bracing under vertical loads. The stability of an open-profile bar with imperfections of form in a nonlinear setting using the Newton-Raphson method is dedicated to the second test problem. The coincidence of the obtained results with the results of other authors and experiments has been confirmed. The work examines the stability of various types of thin-walled bars with imperfections of form under longitudinal loading in a linear setting using the Lanzos method and in a geometrically nonlinear setting using the Newton-Raphson method. It has been researched the combined effect of the initial imperfection amplitude and the eccentricity of applied forces on the nonlinear deformation and stability of thin-walled open-profile bars of the real structure. Dependencies of critical load values and stability loss forms on the amplitude of bar imperfections and the eccentricity of applied longitudinal forces are presented. The influence of the model and amplitude of geometric imperfections on the stability of thin-walled open-profile bars is confirmed. Keywords: open profile thin-walled elastic bars, imperfections of form, static stability, critical loads, stability loss forms, finite element method.