UkrainianProfessional Education

Abstract

In the calculations of structural reliability, it is mainly considered that the laws of distribution of random values of resistance and load effect obey the normal law (Gauss’s law). This law is convenient to use and the most widespread. Therefore, it has found wide application in reliability theory for solving most problems. The law of distribution is symmetric, that is, random variables are distributed symmetrically relative to its center (mathematical expectation). But, as experimental studies show, both the material resistence and the load effect on the structure in most cases are subject to asymmetric laws. The asymmetry of the material resistance can be neglected in most practical cases, but failure to take into account the asymmetry of the load effect can lead to significant errors in determining structural reliability. The authors chose two laws with different degrees of positive asymmetry to approximate the load distribution, namely gamma and lognormal laws. The normal (symmetric) law was used for the resistence distribution law. The results of reliability calculations that take into account different load distribution laws are presented in the form of a table and a graph. The graph shows the dependence of structural reliability on the reliability index for symmetric (PN) and asymmetric (PNG, PNL) laws. All calculations were performed using the Mathcad complex, which allows calculating values with sufficient accuracy. The issue of how to choose the distribution law for the load effect obviously depends on the operation mode of a particular bridge and should be based on appropriate statistical studies. The purpose of this paper is to show the need for taking into account the law of asymmetry in order to determine the structural reliability. Eurocode norms also require to take into account the asymmetry of distribution laws

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