Meditations on Equi-Strength, Equi-Stability, Equi-Reliability and Optimal Design
DOI:
https://doi.org/10.32347/2410-2547.2026.116.3-12Keywords:
equi-strength, equi-stability, equi-reliability, reliabilityAbstract
Traditional approaches to the design of building structures are considered, which are based on the full use of their resistance and rely on the search for conditions of equi-strength, equi-stability or equi-reliability of system components.
Attention is drawn to the fact that the equi-strength of structural elements tacitly assumes their equal role in ensuring the reliability of the system as a whole, when the failure of at least one element is a critical event. That is, the structure is considered a system with sequentially (in the sense of reliability) connected elements, and this often does not correspond to reality. That is why the optimization conditions do not coincide with the principle of equi-strength. Examples of deliberate deviation from equal strength in order to increase the survivability of structures are given.
The design of equi-stable structures is based on the independence of various forms of loss of stability, but such independence is violated when switching to nonlinear analysis. Then it turns out that structures designed according to the principle of equi-stability have a special tendency to the destabilizing effect of initial imperfections, and here there is a possibility of destruction of structures, which has an avalanche-like character.
It is emphasized that it is quite logical to formulate the same requirements for the reliability of functioning (target reliability levels) for objects of approximately the same degree of responsibility, regardless of the material from which they will be designed and the type of structural scheme. The condition for the equi-probability of the occurrence of design loads is also valid, regardless of the number in the design combination. But the equal reliability of structural elements may not correspond to their functional purpose, which leads to a decrease in overall reliability. A simpler example is ensuring survivability by using key elements with increased reliability.
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