The dissertation is devoted to the study and solution of the problem of sections with transitional stiffness on approaches to bridges analytically and experimentally through the use of numerical analysis, experimental tray research by centrifugal method and field tests.
The first section of the dissertation analyzes the problem of areas with a transitional stiffness index in modern construction: the problems that arise in such areas, the preconditions for their occurrence and the nature of development, solutions used in Ukrainian and world bridge construction.
The result of the study of the existing knowledge base of the European experience of the bump at the end of the bridge issue was the compilation and structuring of the causes of its occurrence, methods of detection and solutions. Ways to solve the problem of the bump at the end of the bridge are formed into three subgroups depending on the depth of immersion in the construction and the type of reinforcement. Based on the collected data, 3 reinforcements of the transition section at the approach to the bridge were developed: Gabion box reinforcement, Reinforcement with soil-cement piles and Reinforcement with sorted and reinforced soils.
In the second section of the dissertation the research of stress-strain state (SSS) of sections with transitional stiffness on approaches to bridges had been performed.
First of all, the section considers the main models of mathematical modeling of soil structures, methods of mathematical analysis, highlights the main achievements and results of the conducted research of SSS of soil structures with the help of FEM and performs a numerical analysis of sections with transitional stiffness on the model of the approach of a real railway bridge.
As a result of mathematical modeling, isopoles of loads and displacements along the Z axe for the transition section with each of the types of reinforcement had been obtained.
The maximum vertical displacement in the model №1 is 5.04 mm, in the model №2 - 1.72 mm, in the model №3 - 2.65 mm, in the model №4 - 1.55 mm.
In the third section, an experimental study of the SSS of the construction of the transition areas by the centrifugal method had been performed.
The simulation is performed for the original model and each of the three types of amplification proposed in Section 1. A 1:50 scale model had been built in a metal tray.
As a result of the experiment, the subsidence intensity of the reinforcement model in different horizontal and vertical coordinates and the maximum subsidence of the structure under load were obtained.
Comparison of the obtained results shows that the use of all three options of reinforcement has a positive effect on reducing vertical deformations (2.10… 3.86 times).
In the fourth section of the work, field studies of the area with transitional stiffness on the approach to the railway bridge had been performed.
The test had been performed by several methods: estimation of the vertical modulus of track elasticity at the transition section; determination of dynamic vertical forces acting from the train wheels on the rail and determination of track subsidence by the leveling method before and after reinforcement.
The first test method is performed by applying a vertical load on the rail at different points of the horizontal profile. As a result of the test, the values of vertical stiffness and vertical modulus of elasticity of the track at different points of the transition section had been obtained.
In the second test method, the method of measuring axle accelerations is used to measure the vertical forces acting from the train wheels on the rail. As a result of the test, the vertical forces and accelerations that occur in the area of the bump at the end of the bridge had been obtained.
The third part of the section is devoted to confirming the effectiveness of reinforcement of sections with transitional stiffness. For this purpose, the track had been leveled and its profile had been obtained, after which reinforcement had been performed, after which re-leveling had been performed after 12 months.
The scientific novelty of the obtained results is as follows:
• new regularities of the stress-strain state of the transition section;
• for the first time in Ukraine, an experimental model of the transition section for centrifugal modeling was built;
• the mathematical model of the transition section has been improved;
• three new methods of reinforcement of the transition sections on the approaches to the bridges have been developed.
The scientific results obtained in the dissertation can be used to model the transition areas and a deeper study of their nature. The constructed mathematical and experimental models can be used for research and development of soil reinforcement, including transition areas.
The developed reinforcement methods can be used to increase the stiffness of new or existing transition sections of railway or road bridges.
