| When certain thin-walled frame structures are twisted, the shear stresses and strains are relatively much larger than those in a solid rectangular beam, furthermore, there is a so-called warping of the cross-section of thin-walled frame structures. So, in the finite element analysis of thin-walled structures, there are not six but seven degrees of freedom at each node of the beam, in which the seventh degree of freedom accounts for warping deformation of the cross section and serves as a measure of the warping of the cross section. Moreover, because thin-walled structures can undergo large rigid-body motion without sustaining large strains, it is very important to take geometric nonlinearity into account when studying the mechanics performance of thin-walled structures. The purpose of this thesis is to explore the geometric nonlinear seismic response time integration of open thin-walled frame structures. In order to accomplish this purpose, the software XFINAS is adopted, which is applicable to the finite element analysis of open thin-walled frame structures and can be used to analyze static and dynamic, linear and nonlinear problems, but there are few examples for the geometric nonlinear seismic response time integration. To develop this thesis, the theory of open thin-walled structures is presented, and the finite element analysis software XFINAS has been introduced carefully, and its literature and operating procedure have been summarized. Meanwhile, in order to make the software run smoothly and efficiently, lots of work has been done to debug and optimize the software XFINAS. Based on the work mentioned above, the nonlinear seismic response time integration of open thin-walled frame structures has been introduced in detail. Through modifying the input procedure of XFINAS, its application to the nonlinear seismic response time integration of open thin-walled structures has been explored, and numerical examples are presented to verify the reliability of the software XFINAS.
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