Diagnostics of steel structures with the dynamic non-destructive method

The method of the assessment of steel structures mechanical properties is considered with the nondestructive test by conical indentation. The nondestructive evaluating of the steel mechanical properties in real structures is widely spread in many applied problems. Dynamic indentation method is one of the most effective because of compatibility and accuracy. For this purpose, the static and dynamic problem of axisymmetric elastic-plastic truncated cone indentation is solved, and the results are compared with finite element analysis and experimental data. The method of nondestructive evaluating of mechanical characteristics is suggested and devise of the realization of the method is tested at real structures. The method is tested on steel railway bridges that are being operated for more than 60 years. As a result, zones with lower strength values were identified, and recommendations for strengthening the design were given

Developing Environmentally Sustainable and Cost-Effective Geopolymer Concrete with Improved Characteristics

Improving the efficiency and quality of construction mainly depends on the cost of building materials, which is about 55–65% of total capital-construction costs. The study aimed to obtain geopolymer fine-grained concrete with improved quality characteristics that meet the construction field’s sustainable development criteria and that have environmental friendliness, economic efficiency, and advantages over competing analogues. The dependences of strength characteristics on various compositions of geopolymer concrete were obtained. It was found that the most effective activator is a composition of NaOH and Na2SiO3 with a ratio of 1:2. The increase in the indicators of the obtained geopolymer concrete from the developed composition (4A) in relation to the base control (1X) was 17% in terms of compressive strength and 24% in tensile strength in bending. Polynomial equations were obtained showing the dependence of the change in the strength characteristics of geopolymer concrete on the individual influence of each of the activators. A significant effect of the composition of the alkaline activator on the strength characteristics of geopolymer fine-grained concrete was noted. The optimal temperature range of heat treatment of geopolymer concrete samples, contributing to the positive kinetics of compressive strength gain at the age of 28 days, was determined. The main technological and recipe parameters for obtaining geopolymers with the desired properties, which meet the ecology requirements and are efficient from the point of view of economics, were determined

Comparison of the efficiency of neural network algorithms in recognition and classification problems

The article is devoted to the problem of comparing the effectiveness of feedforward (FF) and convolutional neural networks (CNN) algorithms in the problems of handwritten digit recognition and classification. In recent years, the attention of many researchers to the FF and CNN algorithms has given rise to many hybrid models focused on solving specific problems. At the same time, the efficiency of each algorithm in terms of accuracy and labour intensity remains unclear. It is shown that in classical problems, FFs can have advantages over CNN in terms of labour intensity with the same accuracy of results. Using the handwritten digits data from the MNIST database as an example, it is shown that FF algorithms provide greater accuracy and require less computation time than CNN

Bending strength assessment of chemically-heat-strengthened Novikov gearing

The article is devoted to the refinement of the flexural strength assessment of surface-strengthened gears with Novikov’s engagement. For standard involute wheels the results that were calculated in accordance with existing regulations and experiments could differ by an order of magnitude, or even more, then for Novikov’s transmissions, only partial recommendations based on experiments are relatively reliable. The influence of several factors, such as the possible initiation of flexural fractures under the action of contact stresses on the tooth’s leg, as well as the peculiarities of cyclic loading of gear teeth with two lines of engagement, have not been studied in practice. The purpose of this article is to assess the influence of tensile stresses on the boundary of the instantaneous contact spot in the conditions of reducing the plastic properties of the material due to thermal (chemical-thermal) treatment. The presence of a dangerous cross-section on the border of the active and transitional sections of the tooth profile is presented, which may not coincide with the area of action of the maximum tensile stresses, in which two essentially different types of stress-strain state will alternate, which considerably complicates the assessment of accumulation of fatigue damages

Metal structures diagnosis by truncated cone indentation

The method of the steel structures diagnosis is considered with nondestructive test by truncated cone indentation. Recently, great interest in the nondestructive evaluating of the steel mechanical properties at real structures is developed in many applied problems. Dynamic indentation method is one of the most effective because of compatibility and accuracy. For this purpose static and dynamic problem of axisymmetric elastic-plastic truncated cone indentation is solved and the results are compared with finite element analysis and experimental data. The method of nondestructive evaluating of mechanical characteristics is suggested and devise of the realization of the method is tested at real structures

Static analysis of a reinforced bimodulus beam on elastic foundation

The work considers a reinforced concrete beam made of bimodule material on an elastic Winkler base. The influence of the number of reinforcing bars located in the stretched zone on the maximum normal stress and the maximum deflection is numerically investigated. The choice of the cross-section dimensions, such as the width and thickness of the flanges, the height of the beam, causes particular difficulties and is limited by the need to determine specific ratios of I-beam sizes. Numerical investigation allows analyzing the influence of the width of the I-beam flange that is in contact with the elastic base on the maximum tensile stresses and maximum deflection. The effect on the stressed-deformed state of the various cross-section forms is carried out in work for an I-beam, a rectangle, and a T-beam. Related to the fact that for many building materials the elastic moduli for tension and compression differ, it became necessary to determine the influence of material heterogeneity on the stress-strain state of the elements of building structures. In particular, the widespread use of reinforced concrete beams as elements of band foundations requires a refinement of the stress-strain state study taking into account the heterogeneity of concrete

Buckling analysis of rod structure of the two-tier dome

The paper deals with the problem of calculating the rod structure of a two-tier dome for stability. Such structures consisting of straight rod elements are widely used in practice and have a number of significant advantages. First of all, it is a high rigidity with a low mass. Also, this type of construction is well resistant to dynamic loads. At the same time, the dome model allows for the bifurcation of points on the equilibrium state curve of the system. The problem of the dynamic stability of double dome is solved by the principle of stationarity of total potential energy of the system. The analysis of the obtained solution is carried out, and the equilibrium state diagram for a two-tier core dome is constructed

Layered structures mechanical properties assessment by dynamic tests

An effective method of the layered structures mechanical properties determination is presented. The method is based on the non-stationary analysis of the structure response that is acted by impact load on the surface of multi-layered structure. The assessment of the design parameters using a genetic algorithm is performed. During the solving procedure there are several methods for breeding and selection processes are used, that demonstrated different results. The most appropriate parameters for described algorithms are selected and analysed