Nonproportionally Loaded Steel Beam-Columns and Flexibly-Connected Nonsway Frames

A theoretical study of the inelastic stability of nonproportionally loaded steel beam-columns and flexibly-connected frames is conducted. Specifically, solution techniques are formulated to predict the nonlinear behavior of cross sections, spatial beam-columns, and nonsway plane frames under the combined influence of imperfections, flexible connections, and nonproportional loads. A set of new inelastic slope-deflection equations for imperfect members are derived and their use illustrated through in-depth studies of flexibly-connected portal and two-bay two-story frames. These equations are derived from a system of nonlinear ordinary differential equations. The member studies are carried out using a second-order finite-difference solution to a set of nonlinear equilibrium equations, and coupled to a tangent stiffness procedure for cross sections. The majority of the theoretical studies are carried out on a conventional sequential computer. Efficient concurrent computational algorithms are also presented for biaxial bending and column stability problems. Results are obtained using a multiprocessor computer known as the Finite Element Machine. A critical appraisal of the conventional tangent modulus approach is presented in light of the analysis which includes elastic unloading of the material. It is found that the tangent modulus approach results in a fictitious ductile behavior. Furthermore, is is also realized that there is a dramatic difference in the nonlinear behavior between the proportionally and nonproportionally loaded structures. It is also observed that the proportionally loaded structures lead to rather unconservative peak loads. Additionally, members as integral parts of a frame may exhibit significantly different load-deformation behavior as compared to that of isolated members. The study on members and frames shows that nonproportional loads have a significant effect on their behavior and strength

Substructure analysis using NICE/SPAR and applications of force to linear and nonlinear structures

Parallel computing studies are presented for a variety of structural analysis problems. Included are the substructure planar analysis of rectangular panels with and without a hole, the static analysis of space mast, using NICE/SPAR and FORCE, and substructure analysis of plane rigid-jointed frames using FORCE. The computations are carried out on the Flex/32 MultiComputer using one to eighteen processors. The NICE/SPAR runstream samples are documented for the panel problem. For the substructure analysis of plane frames, a computer program is developed to demonstrate the effectiveness of a substructuring technique when FORCE is enforced. Ongoing research activities for an elasto-plastic stability analysis problem using FORCE, and stability analysis of the focus problem using NICE/SPAR are briefly summarized. Speedup curves for the panel, the mast, and the frame problems provide a basic understanding of the effectiveness of parallel computing procedures utilized or developed, within the domain of the parameters considered. Although the speedup curves obtained exhibit various levels of computational efficiency, they clearly demonstrate the excellent promise which parallel computing holds for the structural analysis problem. Source code is given for the elasto-plastic stability problem and the FORCE program

Two-dimensional finite element analysis of rectangular panel with hole using NICE/SPAR

A panel 30 in. long, 11.5 in. wide, with a 2.0 in. diameter hole at the center is analyzed. Since a two-dimensional analysis is conducted, the thickness of the panel is taken as unity. Owing to the symmetry, it is sufficient to analyze only one fourth of the panel with appropriate boundary conditions