The life cycle of a construction (or its element) is considered as markovian process with discrete states and continuous time. Five operational states have been accepted, in which the construction may be. The corresponding system of differential equations is obtained for the case of a homogeneous markovian process with a constant conversion rate (Kolmogorov system). The method of uncertain coefficients is applied to solve the system of equations in analytical form. The obtained solutions make it possible to determine the probability of finding the construction in a particular state as well as the most likely transition time from one operational state to another. Security function defined as the probability of not finding the construction in its last (inoperable) state and the failure rate function. The graphs of the probability of finding a construction in each of the five states, reliability and failure rate functions are presented and investigated. The obtained analytical dependences make it possible to determine the longevity and residual life of the work both individual elements and structures as a whole and optimize scheduling for ongoing maintenance work, significantly improve the performance of the structure, reduce the cost of repair work and extend the life of the structure.

Introduction. Hydraulic calculation of bridges is one of the most important stages in determining its basic geometric parameters. Therefore, it should be based on the exact equations of hydraulics that characterize the behavior of water flow. Currently, the hydraulic calculation of a small bridge is based on an empirically established dependence, which is that the compressed depth under the bridge hc is associated with the support H approximate dependence hc ≈ 0,5H and is independent of the compression of the flow bridge crossing. In this work, it is theoretically proved that taking such a relationship between depths, you can get quite large inaccuracies in determining the depth in the compressed section hc, and hence in determining the speed in the calculated cross section of the bridgehead. Results. Based on the three basic laws of physics, namely: the law of conservation of mass (continuity equation), the law of conservation of energy (Bernoulli equation), the law of momentum (equation of the momentum change theorem), obtained an analytical relationship that establishes a relationship between compressed depth parameters hc and support H at different degrees of flow compression ε. Based on this dependence, an equation was obtained that establishes the relationship between the flow rate Q and the pressure in front of the bridge H. The obtained equation is similar in form to the flow equation through a wide-threshold spillway, with the difference that the flow coefficient m(ε) in the obtained equation depends on the degree of flow compression. Conclusions. The equation for determining the flow rate through the opening of a small bridge taking into account the flow compression is obtained. It is shown that the obtained equation coincides in form with the flow equation, which determines the flow through a wide-threshold spillway. The difference between these equations is that the flow coefficient m(ε) is a function of the flow compression coefficient ε. Using the boundary transition, it is obtained that m(ε) can vary from 1/3 √(2/3) to √0,5. Graphs are presented, which allow to analyze the change of hydraulic characteristics of the flow depending on the compression coefficient ε.

The analysis of the literature devoted to calculation of hydrotechnical structures showed that there are recommendations that take into account the influence roughness of the channel on magnitude transformation transit flow of liquid along the length of the channel. But these recommendations are difficult to apply to reclamation systems, which include complexes of hydraulic engineering and transport facilities, because they do not take into account the characteristic features of unsteady fluid movement in such systems. Unfortunately, as of today, this issue has not been adequately addressed in modern scientific literature. The article considers the issue of determining the roughness coefficient based on the materials of field experiments on irrigation systems of Ukraine for its further use in the Saint-Venant equations for unsteady water movement in open prismatic channels. At one time, professor V.O. Bolshakov applied the method of running according to the implicit difference scheme, provided that the roughness coefficients are known, to solve the Saint-Venant equations. The authors conducted an analysis errors of field measurements of maximum depths, calculation area of live sections, etc. The absolute error of finding the drop in water levels in individual sections of the channel was determined. The results. Among the issues that were covered in the discussed publication, the main attention was paid to the issue of studying the influence of the roughness coefficient on flow elements during unsteady motion in meliorational (irrigation) systems. Also, the characteristics conducted field measurements are given, a detailed overview field data is provided, and the measured parameters at different sections research channel are listed. Conclusions. An indicative evaluation and analysis errors of the performed measurements was carried out, and recommendations were given for determining the average values of roughness coefficients for irrigation channels (channels) with a well-planned bottom and slopes, as well as for banks not covered with vegetation. The results of data processing of field observations are summarized in a table, which presents a comparison calculated values of the roughness coefficients.

The article is devoted to topical issues of the influence of hydraulic structures on the behavior of channel flow. Issues related to the operation of hydraulic structures located on irrigation canals were considered: - the influence of the degree of flooding on the elements of unsteady movement in open channels; - the influence of flow compression on the elements of unsteady motion in open flows. Quantitative assessment of the impact degree of flooding and compression on the elements of the flow during steady motion was carried out taking into account the recommendations of prof. Bolshakova VO, which are based on the use of the method of prof. Vasilieva OF The question influence of hydraulic structures on the behavior of the channel flow was solved using the equations of Saint-Venan by the numerical method, namely the method of run by the implicit-difference scheme. To close the system when using this method, the following conditions were taken into account: a - initial; b - left and right boundary conditions. The initial conditions are the presence of uniform movement in the channel. The left boundary condition is determined by the schedule of water supply to the channel, which has the form of a triangular hydrograph. The right boundary condition is determined by the known formula of a spillway with a wide threshold. The initial data were obtained from field observations. Quantitative assessment of the impact of flooding and flow compression on the final flow, velocity and depth results was performed. The issue of distribution of the support along the channel bed, which was formed due to the compression of the flow, was solved using the recommendations of E.V. Eremenko. The equation of flow continuity was considered - under the condition of changing the volume of water in the elementary section of the channel. The time of increase in the volume of water due to compression was determined from the formula obtained in the calculation process. Based on the condition that the time factor is a known value, it is possible to obtain a mathematical expression that determines the length of the propagation of the compression effect. Thanks to the obtained formulas, the calculated graphs of the relative maximum depth depending on the degree of flooding were constructed. With the help of these graphs it is possible to solve the problem of water supply in irrigation canals in the presence of flooding and compression of the flow (in case of unsteady movement).

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