Optimal design of nonlinear framed structures under multiple loading conditions based on a stability criterion

An optimization-based design methodology is presented for improving the strength and overall stability of framed structures. The design methodology is a multiple-objective optimization procedure whose objective functions involve the buckling eigenvalues and eigenvectors of the structure. Designs are constrained to have constant weight. An iterative optimality criterion method is used to solve the optimization problem. The method provides a general tool for designing complex structures with nonlinear behavior and generally leads to designs with better limit strength and stability while avoiding nonlinear analysis in the optimization cycle. The approach is indirect, but is effective and efficient.The design procedure is developed for 2-D and 3-D nonlinear framed structures. Development and application of the optimization procedure for planar framed structures is presented first and is then extended to space-frame structures. Three-dimensional design problems are more complicated, but they yield insight into the real behavior of the structure and can help avoid some of the problems that might appear in the planar design procedure such as the need for out-of-plane buckling constraints.To control the vibration characteristics of the designs, frequency weighting functions are introduced and incorporated into the objective function. These weighting functions provide information about the vibrational characteristics of the design and can be used to avoid undesirable dynamic effects, such as resonance, by pushing the structure away from it while improving the overall stability and strength of the design.One of the novelties of the new design methodology is its ability to efficiently model and design structures under multiple loading conditions. These loading conditions include different factored loads, components of an earthquake, and geometric imperfections and can be applied to the structure simultaneously or independently.Several examples are presented to evaluate the validity of the underlying assumptions and to examine the performance of the procedure. By way of example it is shown that by improving the overall stability characteristics of structure under static loading, the dynamic performance of the structure is also improved.U of I OnlyETDs are only available to UIUC Users without author permissio