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The widespread use of polymer composite materials is largely constrained by the complexity of predicting the characteristics of their stress-strain state under cyclic types of loading. Due to the poor knowledge of the behavior of polymer composite materials under this kind of loading. At present, it is rather difficult to predict the durability of polymer composite materials under static types of loading, and the available methods for materials of a crystalline structure and polymers are not always applicable to them. Insufficient theoretical and experimental data on the assessment of the stress-strain state of polymer concretes under prolonged loading. Under long-term action of cyclic loads, changes in the structure of polymer composite materials occur due to local self-heating at the tops of growing submicrocracks and the associated change in the elastic-hesteretic properties of the material. In this case, the energy of fatigue manifests itself, when the simultaneous multifactorial cyclic action of natural and force stresses leads to an effect that exceeds the total action of certain types of stresses. And, if such processes have been sufficiently studied for wood, a natural polymer material, then for artificial conglomerates, such as polymer composites, these issues require careful study. Studies of the endurance of epoxy polymer concretes were carried out on samples of prisms 100x100x400 mm according to the method developed by the authors. The formula was used to determine the minimum number of samples required to build endurance lines. The value of the cycle asymmetry coefficient was taken equal to 0.6. The value of the maximum cyclic loading was taken from 0.62 Rв with a gradual decrease. The values of the endurance limit of an epoxy composite material under cyclic loading Rв,pul = 0.43 Rв or 93.72 MPa were obtained, which makes it possible to judge the sufficient durability of this material.

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Introduction: the article is dedicated to assessing the condition with respect to use for traffic methods of bridges as part of hydraulic structures (dams, hydroelectric power stations, locks). The main factors affecting the structural element’s durability included in the composition of the hydraulic structures are dynamic loads (applied repeatedly and repeated) affecting the bay due to the hydrodynamic effect; temporary, moving loads from passing highway transportation, along the top of the structure (along the roadway); harmful chemical impurities contained in the water passing through the structure. Under the influence of the above-mentioned factors, defects and damage occur in the hydraulic facilities’ structural elements. Methods: the authors assessed the actual state of the material of the operating structure. To assess structures and materials actual state during the bridge structure inspection work, the following instrumental measurements were performed on as-built structural elements: leveling the top of the sidewalks and the roadway; materials strength determination of the main supporting structures by nondestructive methods; thickness measuring the asphalt concrete pavement of the roadway; determination of the degree of carbonation of concrete; identification of defects in the elements of the bridge. The actual structure’s concrete strength was determined by nondestructive testing methods: (1) by the method of the elastic rebound; (2) by the shock pulse monitoring method; (3) an indirect method of concrete strength ultrasonic testing based on the revealed relationship between the method of separation with shear test and methods – shock pulse and elastic rebound. Results: technical condition and bridge safety indicators calculation as a hydraulic structure element was executed. Discussion: technical examination results of the bridge structural elements and instrumental studies confirm the conclusion about the repair measures need with high-strength concretes and protective coatings based on polymer composite materials. Final report: following the emergency scenarios a numerical estimate table for the quantitative and qualitative parameters list was made, parameters corresponding to a particular structure state. Thus, according to the scenario related to the 3rd accident group, the bridge technical condition is assessed as limited operable, and the safety level is reduced.