ПРОПОЗИЦІЇ ЩОДО ЗМІНИ НАВАНТАЖЕННЯ НА МОСТИ

Abstract

Introduction. Bridge DBN V.1.2-15:2009 «Loadings and impacts» is the document that raised the level of calculated traffic loadings on bridges and bring their values closer to the values of LM1 model of Eurocodes. But the characteristic loadings were remained at the old level, which violated the principles of reliability calculations, according to which the characteristic loadings should deviate from the average values by 5 standards at least. Problem statement. Estimated vehicle loadings of the AK model in DBN B.1.2-15:2009 in compare with LM1 model of Eurocode EN 1991-2 and the track model according to US AASHTO LRFD standards shows that there is a certain balance between them. The calculated loading according to the standards of Ukraine occupies an intermediate position between the standards of Europe and the United States. However, the level of characteristic loadings is almost twice lower in compare with in Eurocode. This is a significant drawback of DBN, because it reduces the level of reliability of calculations based on the second group of limit states. Purpose. The article is devoted to the search and analysis of proposals for loading changes. Materials and methods. The article provides proposals for changing some loading parameters of AK model in order to maintain the level of calculated loadings and increase the characteristic loadings for approaching LM1 EN 1991-2 model loading. Results. In general, the changes proposed in the article will make it possible to raise the level of reliability of calculations according to the II group of limit states to the level of reliability of Eurocodes; at the same time the characteristic values of forces are 20 % lower than the values of LM1 model (except for bridges with one lane); calculated values of forces are (8–10) % lower than the values from the LM1 model (except for bridges with one lane); to simplify the existing loading model and to exclude additional lanes of loadings, to exclude the installation of pairs of tandems when loading lines of supporting moments impact. Conclusions. In this article, we did not touch the issue of introducing a single weighted average reliability coefficient for all permanent loadings. The existing coefficients cannot be substantiated due to the lack of reliable coefficients of variation. Now, a reliability coefficient of 1.25 has been introduced for all self-weight loadings, except for the pavement. And for pavement the coefficients are 1.5 — if the bridge is outside the city and 2.0 — if the bridge is in the city. At one time this was justified by the fact that there were known cases when the pavement on city bridges was doubled during reconstruction of the streets. But now there are no such cases. And if we take 1.5 for the weight of the pavement and 1.25 for the other weight, then for the own weight of all bridge structures we can take the coefficient γf = 1.35.