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Comparison of design and actual reliability indices of a reinforced concrete road bridge under the influence of traffic flow loads
Rudakov I., Kozak N.
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Currently, the semiprobabilistic approach is employed in the practice of bridge design in Russia to account for uncertainties in loads and material properties through reliability coefficients. The semi-probabilistic approach is convenient to use, but it has several disadvantages. Firstly, the use of constant coefficients fails to consider the actual characteristics of traffic composition on specific roads. Secondly, assessments utilizing the semiprobabilistic approach provide only qualitative outcomes (for instance, confirming that a structure meets the conditions for the first group of limit states) and do not allow for a quantitative evaluation of the probability of structural failure. This study employs a full probabilistic approach to determine the reliability index (β) of a cross-sectional ribbed reinforced concrete span structure in a road bridge context. The loading conditions of the span structure were considered using both a model of design loads (taking into account its conversion to a full probabilistic supply) and a model of loads from actual traffic flow, for which data from weigh stations on Russian highways were analyzed and distributions of heavy vehicle masses were constructed. The SOFiSTiK software suite was used as a tool for conducting probabilistic analysis, utilizing the special RELY module for probabilistic calculations, which allows for computations using FORM and SORM methods (First-Order and Second-Order Reliability Method). The results of comparing reliability indices indicated that, for the specific case examined, the actual reliability index is 13 % lower than the design index and nearly 40 % lower than the target reliability index adopted according to recommendations from foreign standards. The algorithm developed during this research can be further applied to determine the reliability indicators of existing operational structures.
Influence analysis of the connective elements failures on the road bridges steel reinforced superstructures service reliability
Kozak N., Syrkov A., Bystrov V., Yaroshutin D.
The paper considers the influence issues of connective elements failures, in particular flexible pin stops, on the road bridges steel reinforced superstructures service reliability. The authors have formulated possible criteria for the superstructure failure both for the first and the second groups of limit states, and also developed scenarios of connective elements exclusion from the structures operation, that are modeling the failure of individual connective elements in the operation process. For five finite element models of road bridges steel reinforced superstructures a numerical experiment on modeling of the connective elements exclusion from the operation of the structure was carried out. The calculation results for each scenario and for the partial scenario realization levels were analyzed in terms of possible superstructures failures as a whole. Numerical experiment results have shown that at the exclusion of a separate small group of connective elements increases the maximum stresses in the over-supported beams sections by up to 3 %, and further development of the connective elements disconnection scenario can lead to an increase in stresses by 20 %. It is concluded that for existing steel reinforced superstructures the risk of superstructures failure under normal operating conditions due to disconnection of connective elements is low, even in the case of almost unlikely complete disconnection of all connective elements. Nevertheless, the exclusion from operation of connective elements may be more critical in cases of abnormal bridge structure operation or in cases of significantly lower engineering reserves of the structure in terms of strength and stiffness.
Operating regime investigational study of steel-reinforced concrete superstructure flexible pin stops of the existing road bridge
Kozak N.
In the article, the author published the full-scale experiment results on an existing steel-reinforced concrete road bridge, carried out to determine the actual parameters of the operation regime of the interconnection elements — flexible pin stops. This work was carried out as part of the author's dissertation research in the field of improving methods for testing the elements' endurance of the steel-reinforced concrete superstructures interconnection and is a development of the previously conducted comprehensive comparative analysis of existing models for testing endurance. The article gives a detailed description of the conditions for conducting and methods of a two-stage experiment, which includes short-term and long-term parts, as well as a detailed description used for processing experimental data for each of the stages. Based on the results of the experiment's short-term part, when compared with the results of finite element modeling of the operation of the stops, the possibility of using existing computational models to describe the actual model operation was confirmed. Also, within the framework of the short-term part, according to the conducted dynamic tests results with the moving load passage through the threshold, the presence of a significant dynamic component of the resulting forces in the interconnection stops was revealed. During the second long-term part of the experiment, a continuous recording of stresses in the interconnection elements from the passage of an unregulated traffic flow over the bridge was made. The article presents both direct survey data (tensograms) and the results of their further processing in terms of damage accumulation analysis; also, the accumulated damages values from actual traffic loads are compared with the expected values in the calculation according to some design standards. Intermediate conclusions based on the experiment results are formed and directions for future work within the scope of this study are indicated.
