Using the criterion of resistibility to assess of a structural limit state

Introduction. Subject of research: behaviour characteristics of an arbitrary structure under the loads that approach the limit load value. Goals: development of an objective and sufficiently universal methodology for the identification of the bearing capacity of a structure, which could allow to stop using any subjective assessments of their limit bearing capacity. Materials and methods. Behaviour characteristics are assessed by analyzing a curve of equilibrium states. The curve is constructed using the characteristic displacement, understood as the generalized displacement q, which energetically matches applied generalized force λ in the sense that the product of λdq is the growth of work performed by generalized force λ in respect of the growth of displacement dq. Results. The article shows that the system’s response, no matter what fixed conditions it is in, is not always sufficient for the assessment of the reliability of the system in case of the variable interaction with the environment. The co-authors use the V.V. Katyushin concept about supplementing the notion of the limit state with the characteristics of the system’s beha­viour determined by the velocity of a change in the system’s response caused by the change in the external action. According to the co-authors’ suggestion, the meter should represent the reduction in the slope of the curve of equilibrium states, which characterizes the loss of resistibility and, consequently, it can be used to assess the closeness of the structure to the state of failure, which arises if the resistibility of the system is equal to zero. The suggestion is to use the value of the slope of the curve of equilibrium states as the limit state, when the resistibility has reduced, and the velocity of deformation intensification has gone up 100 times if compared with the behaviour of an unloaded system. This suggestion is illustrated by the case of the analysis of a reinforced concrete diaphragm of a building. Conclusions. The proposed calculation methodology can be applied in the design of loadbearing structural elements, whose finite-element computational model has components that are different from the rod ones.