Some features of nonlinear calculation in the building design system

Abstract. The work is devoted to the analysis of discrepancies between linear and non-linear calculation of building structures that deform under the influence of load. It is recalled that there are two fundamentally different procedures inherent in the design calculation, namely: (i) static or dynamic analysis of the behavior of the mechanical system, the result of which are the parameters of the stress-strain state of the system and (ii) assessment of the possible resistance of the system elements and the structure in general. It is shown that when using linear analysis, these procedures set the content of independent calculation stages, while when using nonlinear analysis, they are combined and mutually influence each other. Attention is drawn to features inherent only to the non-linear version of the analysis, for example, such as: - the impossibility of using rod finite elements without crushing the length of the rod into elementary sections; - the occurrence of tension-compression stress during bending, as a result of asymmetric development of plastic deformations along the cross-section height; - the possibility of realizing extreme responses of the system at intermediate (not extreme) values of load intensity. The problem of determining the limit state of the system, which corresponds to the global assessment of the carrying capacity, is considered. Taking into account the computational difficulties of numerical analysis when the system approaches the state of the mechanism, it is proposed to accept the state in which the resistance of the system decreases by several orders of magnitude compared to the beginning of the load. Attention is also drawn to cases where the limit state is determined by the level of deformation of the system. A description of the main features of the global safety format is given, and a description of the latest known proposals for global reliability assessment and information on the implementation of these proposals in the new edition of the European Design Standards is provided.