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This paper describes the influence of initial shape imperfections of lattice shells on their general stability. An adequate mathematical model for the analysis of the shell instability by using a direct method (FEM) and a shell analogy method is presented. The reduction coefficient k for calculation of the critical load is derived. An illustrative example is used for comparison of the results calculated by the two numerical methods.

The paper deals with mathematical modeling of the structural materials representing their rheological properties. The materials are modeled by more complex models (enhancement of Voigt and Maxwell models). The constitutive equations are derived; the relationships within the creep and relaxation process are developed. The rheological behavior of the materials is introduced. KeywordsRheological models, differential operator form of the constitutive equations, relaxation, creep, retardation and relaxation time intervals, biorheological processes.