Stress-strain state and stability of the Unglichikan open pit walls

Research objective is to identify the features of stress-strained state development and estimate the stability of Unglichikan open pit walls and dump slopes based on calculation, analysis, and estimation with the certified finite element method GenIDE32. The introduction describes features of research object location natural-technogenic conditions and geological history of rocks building up the research object. Research relevance is due to complex solution to deep and high mountain structures design problems, account for construction technologies, and stress-strained state and elements stability determination. Methods of the stress-strained state numerical calculation, analysis, and estimation for the “structure– geological environment” system consists in using all tools of the program’s interface, namely, values, value levels, isolines and graphs for different quantities, including the graphs of stress-strained state behavior trajectories in the space of the stress tensor invariants and relative strains. Results of calculation are presented as the program’s capabilities in graphic representation of the sequential development of mudslides in open pit walls and dump slopes with vertical fissures. Colors of magnitude levels specify the contours of mudslides, while the corresponding shading of finite elements indicates the fissure formation sites. Conclusions. Calculation results proved the stability of the mountain structures for the selected size dimensions of open pit walls and dump slopes.

Ensuring adhesion between the asphalt-concrete road surface and rigid base at the roadbed design stage

Arranging asphalt-concrete layers on a rigid base in the form of cement-concrete slabs can significantly improve the transporting and operational performance of the road surface. Such a structural solution is appropriate in almost all countries of the world since cement-concrete slabs retain high strength for a long time. To prevent the rapid destruction of an asphalt-concrete road surface on a rigid base, it is necessary to ensure reliable adhesion between the layers' contacts and, at the design stage, to test the adhesion strength by estimation. This paper has substantiated a criterion of adhesion strength in the contact between an asphalt-concrete road surface and the rigid base. The calculation involves comparing the active tangent stresses in the contact between layers dependent on the effect of the vertical and horizontal components of the transport load with the magnitude of permissible tangent shear stresses in the contact of layers. The parameters for an estimation model have been established; the stressed-strained state of the roadbed structure has been simulated using a finite element method. When modeling the stressed-strained state and calculating based on the strength criterion, different vehicle traffic conditions have been considered, as well as the effect of temperature on the strength parameters of the asphalt-concrete layer and the tar layer. The conditions for vehicle movement, taken into consideration when designing, correspond to the conditions of movement along the road, along the curves in the plan and profiles, and notion conditions at car emergency braking. Practical recommendations have been compiled for assigning the minimum permissible thickness of an asphalt-concrete layer on a rigid base, which must be followed at the design stage due to the condition for ensuring reliable adhesion between the layers' contacts. The minimum permissible thickness ranges from 2 cm to 10 cm, depending on the conditions of movement, temperature, and the type of tar.

Determining the stressed-strained state of concrete in the zone of exposure to local laser radiation

This paper reports the results of the physical and numerical experiments on determining the stressed-strained state of concrete in protective structures in the region of the effect of local point laser radiation. The software package LIRA10.8 (release 3.4) was used to build a computer model in the statement of a stationary thermal conductivity problem. To this end, the findings from the experimental studies were applied – the resulting temperature distribution and changes in the structure of concrete on the surface and deep into concrete cubes for more than 120 samples of concrete with three levels of moisture content: dried, natural humidity, and water-saturated. This paper gives the parameters of the simulation, the results of a numerical experiment, their analysis, and comparison with the results of a physical experiment. The temperature fields when establishing the dynamic temperature equilibrium, the level of stresses in concrete, derived from the physical experiments, correlate well with the results of the numerical experiment. The maximum temperature determined by the optical method at the surface of concrete was 1,350+50 °С. Deviations at control points do not exceed 12–70 °С in the temperature effect zone and 18–176 °С (1–11 %). At the rated radiation power of 30 W, the second stage of interaction was achieved; at 100 W – the fourth stage for concrete with a moisture content of 0–2.5 %; and, for water-saturated concrete, the fifth stage of interaction with the laser beam. A significant decrease in the thresholds between the stages of interaction between laser radiation and concrete was revealed, especially water-saturated concrete, compared to the thresholds for metals (the thresholds between the third and fifth stages were reduced by 103–104 times). The destruction of the walls of water-saturated pores in concrete occurred under the pressure of water vapor. The tangent stresses, in this case, were 1.7 MPa, and the values for the coefficient Kр, determined by the method of acoustic emission, were in the range of 4‒6. Such results explain the absence of normal microcracks due to the hoop effect. It was established that in the contact zone between a laser beam and concrete, about 90 % of the radiation energy dissipates, and in the adjacent heating zone ‒ up to 77 %. The optimal speed of beam movement when cleaning the concrete surface from organic, paint, and other types of contamination of 0.5–2 mm/s (surface temperature, 100–300 °С) has been proposed

A comprehensive procedure for estimating the stressed-strained state of a reinforced concrete bridge under the action of variable environmental temperatures

This paper reports the full-scale experimental measurements of temperature distribution over the surfaces of bridges' steel-concrete beams under the influence of positive and negative ambient temperatures. It has been established that the temperature is distributed unevenly along the vertical direction of a bridge's steel-concrete beam. It was found that the metal beam accepted higher temperature values. The maximum registered temperature difference between a metal beam and a reinforced concrete slab at positive ambient temperatures was +9.0 °C, and the minimum temperature difference was −2.1 °C. The mathematical models for calculating a temperature field and a thermally strained state of bridges' steel-concrete beams under the influence of variable climatic temperature changes in the environment have been improved, taking into consideration the uneven temperature distribution across a bridge's reinforced concrete beam. The possibility has been established to consider a one-dimensional problem or to apply the three-dimensional estimated problem schemes as the estimation schemes for determining the thermo-elastic state of reinforced concrete bridges. The temperature field and the stressed state of bridges' reinforced concrete beams were determined. It was found that the maximum stresses arise at the place where a metal beam meets a reinforced concrete slab. These stresses amount to 73.4 MPa at positive ambient temperatures, and 69.3 MPa at negative ambient temperatures. The amount of stresses is up to 35 % of the permissible stress values. The overall stressed-strained state of a bridge's reinforced concrete beams should be assessed at the joint action of temperature-induced climatic influences and loads from moving vehicles

Transition from complex strained state to simple one under non-proportional loading: comparison of various approaches

Object and purpose of research. This paper discusses ship structures. Its purpose is to compare the most common methods for transition from complex strained state to the simple one in calculations of fatigue strength under non-proportional loading. Materials and methods. This paper describes the method of absolute maximum principal stresses, the method of signed von Mises stresses, Sins method and critical-plane method. Main results. Analysis of time histories for design stresses obtained as per above-mentioned methods for the simplest examples of non-proportional loading. The comparison of these results was illustrated by a case study (loading of an icebreaker propulsion shaft). Conclusion. It is shown that, of all the methods discussed in this paper, only critical-plane method can fully take the loading process into account. None of the other methods can take into account the changes in orientation of principal stresses, so their results could be both somewhat too high and too low.

COMPREHENSIVE INVESTIGATION OF EXTRUSION OF П-SHAPED BRACKETS. REPORT 7. STRAINED STATE AND STRENGTHENING OF BLANKET DURING RESTRICTED EXTRUSION. PART 1

The solution beginning of the determination problem of the strained state of a blanket during restricted extrusion of П-shaped brackets under the conditions of plane deformation in the general case of a nonaligned placement of the punch and the die is stated. The formulae were obtained, which allow one to determine current coordinates of material points and cumulative strain in the area of plastic strain situated under the extruded thick wall for any specific value of the working stroke of a punch.

Seasonal variations of frequency parameters of Earth’s natural pulsed electromagnetic field

В результате постоянного мониторинга интенсивности импульсного потока в диапазоне очень низких частот, впервые зарегистрировано сезонное изменение частотных характеристик естественного импульсного электромагнитного поля Земли (ЕИЭМПЗ). Исходя из общепринятых физических представлений о причинах появления литосферной составляющей ЕИЭМПЗ, основанных на механоэлектрических преобразованиях в горных породах, можно предположить, что изменение низкочастотной составляющей ЕИЭМПЗ в среднесуточных вариациях интенсивности сигнала может быть связано с изменением физико-механических свойств и структуры литосферы. Дальнейшие исследования зависимости суточных и сезонных изменений электромагнитных полей в различных частотных диапазонах позволят получить новые знания о механизмах формирования ЕИЭМПЗ, оценить долю литосферной составляющей в структуре этих полей. Прикладным применением поставленных исследований будет оптимизация методов и оборудования раннего оповещения активизации опасных геодинамических процессов, новые критерии оценки напряженно-деформированного состояния горных пород. As a result of the experiment, we have recorded for the first time the seasonal change in frequency parameters of Earth’s natural pulsed electromagnetic field (ENPEMF). This effect once studied thoroughly should allow to further advance a physical model of ENPEMF lithosphere component formation and would help to formulate additional stress-strained state of the rock estimation criteria for geodynamic survey methods

Investigation of а stress-strained state of a screw-shape tubes of heat exchangers

Based on the results of the study of the parameters of the air flow inside of the brass screw-shape tube of the heat exchanger, the determination of their optimal geometric characteristics and further modeling of the stress-strain state was performed. Verification of simulation results is carried out on the basis of comparison with the test task.