On the consideration of progressive failure at the stage of design

The stress that affects structures and their mechanical and geometrical parameters are random values. For that reason, the dependability of a construction facility (technical system) is generally evaluated in terms of the probability of no-failure over the estimated period of operation. The paper shows the feasibility of dependability analysis of building systems in the course of their design using logical and probabilistic methods, presents algorithms for regulating their dependability. It examines the feasibility of assuring the dependability of a construction project using the example of a double-span whole hinged beam. The paper also establishes the requirement of accounting for all possible destruction models of a building system. The dependability of a double-span whole hinged beam is estimated based on the probability of non-occurrence of all possible destruction models or one of a set of possible kinematic mechanisms. A kinematic mechanism forms a chain of plastic hinges or a chain of progressive failures of effective sections. In other words, the task of preventing progressive collapse comes down to ensuring the required dependability of both the building as a whole, and its individual members (effective sections) by adjusting qualitative and quantitative indicators of the dependability structure. The dependability of a member is understood as its ability to maintain internal force within the effective section at least as high as the external force. It is shown that correct design solutions, rational choice of materials and load non-exceedance probabilities enables specified dependability of a building system. In some cases that allows saving materials, in others enables lower probabilities of failure. Constructing the dependability structure of a technical system enables a quantitative estimation of the most hazardous design models of destruction, rational management of the choice of safety factors of load bearing members, redistribution of such safety factors, thus preventing progressive collapse. The introduced differential characteristics of the members’ “weight”, “significance”, “contribution” and “specific contribution” allows demonstrating the distribution of the roles of each member within the specified structure in terms of specific problems, including accounting for the possibility of progressive collapse. The study has shown that the removal of undependable vertical load bearing structures does not solve the problem of dependability of a construction project, including protection against progressive collapse. It has been established that the design of structures, including in terms of considerations of progressive failure, must involve constructing a system dependability structure using kinematic analysis, identifying the most important and significant members of such structure and – using special adjustment techniques – obtaining the required structure dependability. That will enable significant resource saving and reduction of costs associated with the development of construction operations.

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