Microcomputer-Based Nonlinear Structural Analysis of Transmission Line Systems

Until recently, calculations needed for the structural design of transmission lines required access to large computers. Advances in both microcomputer capabilities and in nonlinear structural analysis techniques indicate that it is no longer necessary, nor often desirable, to use mainframe or mini computers. The facts are demonstrated by several examples of complex systems (guyed lattice tower, interaction between structures of a flexible system, H-frame, sagtension behavior, etc.). Many transmission line structures or subsystems exhibit pronounced nonlinear behavior. Four sources of nonlinearities are common: 1) geometric nonlinearity of the relationship between cable sag and tension (even if the cable remains elastic), 2) geometric nonlinearity, or so called P - ?? effect, caused by support displacement (common in poles, H-frames or guyed lattice structures), 3) nonlinear stress-strain relationship of a cable (especially for a conductor where creep and permanent stretching occur), and 4) local nonlinear behavior of a component (plastic deformation of a beam element, buckling of a compression member in a lattice ``tension only'' bracing system, etc.). Because of these effects, nonlinear analysis techniques should be available to the transmission line designer. The paper demonstrates that: 1) the right combination of structural element and solution strategy permits the solution of virtually any structural transmission line problem and 2) the solution can be obtained efficiently on the current generation of microcomputers. The first part of the paper discusses how a microcomputer should be used in typical analysis-design applications.