Although the establishment of the maximum acceptable failure probability for structures is not a mandatory requirement in design, it is important to develop a unified system for safety differentiation of bearing structures in public buildings so that people can feel equally safe in all the countries of the European Union. Differences from country to country in safety requirements declared by national codes may be permissible regarding the economic losses only. This study is aimed to clarify the understanding of how to examine a structure regarding the weakest link (element, fastener, system) in the limit state. In this study the authors propose a method for differentiation of structures regarding the variation of bearing capacity, which variates depending on a number of characteristics involved, and the failure mode anticipated when overloading takes place. Variation of bearing capacity is expressed in terms of reliability index variating correspondingly. Differentiation of the safety regarding failure modes anticipated has been developed using the toughness indices as a decisive criterion for the comparable assessment of structural compositions regarding the ability to sustain in the limit state for some period of time. Also, a criterion of possible redistribution of internal forces in the limit state is taken into account. The developed example of the assessment of the target reliability of structures is presented.
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