Resistance of Structural Materials to Deformation in the Case of Linear and Flat Stresses

Annotation: The deformation resistance properties of structural materials in the case of linear and flat stresses are given on the basis of experimental results. The method of estimating the mechanical properties of the material based on the initial deformation diagrams is described. Keywords: Stress, deformation, longitudinal force, internal pressure, stress state, deformation diagram, initial deformation, Yung modulus, Poisson's ratio, anisotropy, strength, yield strength

PHYSICAL PREREQUISITES FOR GAS PERMEABILITY SIMULATION OF MINED ROCK MASS

Purpose. Justification of the gas collectors formation physical model on the basis of research of conformity of permeability of rock mass to the full diagram of rock sample deformation. Methodology consists in sequential analysis of the stages of the complete deformation diagram of the rock specimen under “hard” loading, comparing them with the stages of formation of the high stress zone in front of the lava bottom and statistical analysis of laboratory test results. Results. Based on the rock’s deformation properties analysis and their comparison with the rock sample full deformation diagram, the physical model of formation of gas reservoirs during the development of gas-saturated coal seam is substantiated. Within the solved problem framework, four stages of the complete deformation process are analyzed, namely: elastic, at the limit of strength, out-of-bounds stage and equivoluminal flow zone. The gas collector boundaries, which are the characteristic points of the rock sample deformation diagram in specified deformations mode (the limit of elastic strength and the limit of final strength) are determined. It is proved that the structural and textural features of the coal mass in connection with the course of gas-dynamic processes are manifested in the change in the pores and cracks volume contained in it, which together make the filtration space. Knowledge regarding the transfer of the permeability changes established regularities and free methane accumulation zones formation to the real rock mass, if the process of its forgery is considered as a consistent change of geomechanical states of rocks, is obtained. Scientific novelty lies in the first substantiated possibility of modeling the stress state before the longwall face by equivalent stages of the rock sample destruction in the given deformations mode. Gradual comparative analysis of the internal mechanism of rock samples deformation along the complete deformation diagram allowed establishing causal relationships between geomechanical and gas-dynamic processes in coal mass, and qualitatively characterizing general trends in permeability and volumetric expansion in changes of these samples. Practical value of the work lies in the justification of the principle of construction of a digital geomechanical model for the detection of man-made gas collectors in a mined coal mass.

Characteristics of Dynamic Loading Obtained From Braced Piping Support Under Sinusoidal Shaking Condition

Loads applied to structures by means of vibration can be classified into load-controlled and displacement-controlled loads. The realistic elastic-plastic behavior of structures subjected to seismic loads is not fully understood, and the classification of the load applied to structures by means of earthquakes is unclear. The failure mode differs depending on the load classification, and thus clarifying the classification of the load applied to the structure is useful for designing the structure. This study clarified the realistic load classification of structures under an elastic-plastic response. Vibration tests were conducted using sinusoidal waves as inputs, and the elastic-plastic behavior of the piping supports undergoing buckling or fatigue failure was obtained. The maximum restoring force and the maximum deformation relationship were obtained from the envelope of the time history data of the test results. In addition, it was shown that the classification of the load could be determined from the maximum force-deformation diagram, even in cases involving buckling and fatigue. In the maximum force-deformation diagram, when the change in the ratio of dynamic restoring force to static restoring force is small, a load-controlled load is applied to the structure because the restoring force of the structure follows the change in the input wave. By contrast, when the change in the ratio of dynamic response displacement to static displacement is small, a displacement-controlled load is applied to the structure because the response displacement of the structure follows the change in the input wave.

The Torsion Problem of a Cylindrical Solid Taking Into Account the Material Weakening

The weakening of the material begins reaching a critical level of stress state, is characterized by a decrease in the level of stress during growing deformations and can develop with an equilibrium accumulation of structural damage. The equilibrium accumulation of damage is possible if the given displacements of the boundary points are provided (that is, with “hard” loading) and if the rigidity of the loading system is sufficient. The design becomes unable to withstand the load only when zones with weakened connections are developed enough. Therefore, taking into account the full deformation diagram in the calculations allows to more accurately determine the load bearing capacity of the design. This paper gives an analytical solution for the problem of a homogeneous cylindrical solid torsion with a circular cross section with its hard loading taking into account the material weakening. Piecewise linear approximations of elastic and elastoplastic medium with a linear weakening at the supercritical deformation stage are considered. The diagrams are plotted regarding stress distribution over the cross section are given; the graphs of the maximum torque value and the extreme value of the relative angle of rotation on the parameters of the deformation diagram. The dependences of the torque on the relative angle of rotation of the sections for the stage of initial supercritical deformation, as well as the stage of supercritical deformation and fracture are determined. The graphs of the dependence of torque on the angle of rotation of the section are given. Reserves of the load bearing capacity of the design are identified. It is noted that taking into account the weakening of the material is expedient in strength calculations and in determination of the system’s safety factor.

DIAGRAMS OF VACUUM INSULATING PANEL DEFORMATION DURING COMPRESSION

The possibility of using vacuum insulation panels (VIP) with a granular filler for the manufacture of threelayer enclosing wall panels, floor slabs and coatings is considered. The results of experimental studies of vacuum insulation panels, carried out with the aim of analytically describing the deformation diagrams of VIP panels under the action of a compressive load, are presented. It has been established: deformative properties of vacuum insulation panels with granular filler do not depend on the size of the filler particles, but depend on the volume content of the filler; a deformation diagram describing the relationship between stresses and relative deformations during compression of a vacuum insulating panel with a granular filler can be approximated by the function G. B. Bülfinger. The results obtained make it possible by calculation to determine the stress state in flat plating sheets during local load transfer.

Strength and Deformability of the Concrete Core of Precompressed Concrete Filled Steel Tube Columns of Annular Cross-Section

The advantages of short concrete filled steel tube columns with a precompressed concrete core are presented in the article. Particular cases, where such compression is most appropriate, are listed. Taking into consideration the structural features of concrete filled steel tube columns it is recommended to calculate their bearing capacity on the basis of deformation model of reinforced concrete. The reliability of this calculation will be largely dependent on the conformity of the accepted diagram of the concrete core deformation with its actual behavior. Formulas for determining the strength of precompressed concrete core and the ultimate strain of its shortening are proposed, which allow constructing the sufficiently accurate deformation diagram.

Normal Sections Calculation of Bending Reinforced Concrete and Fiber Concrete Elements

The basic principles of the normal sections calculation of reinforced concrete and fiber reinforced concrete bending elements are considered. In the article the power and deformation methods of calculation of reinforced concrete and fiber concrete elements of rectangular cross-section are presented. The deformation model of the calculation of reinforced concrete and fiber concrete elements is presented in the framework of the method of calculation resistance of the section. This method makes possible from the common methodological positions to perform calculations of reinforced concrete and fiber concrete elements. Namely, to select reinforcement and to determine the carring capacity. The proposed deformation model for calculating fiber concrete elements is based on generally accepted preconditions. A hypothesis of plane cross sections is accepted as fair. The deformation diagram of compressed concrete is described by a nonlinear function with established parametric points. Distribution of stresses in stretched concrete is taken rectangular with corresponding coefficients which are taken depending on the type of deformation diagram. Determination of the carring capacity of fiber concrete elements occurs under extreme deformation criteria. Two cases of destruction of the investigated elements are considered. The first case is the destruction due to the achievement of limiting deformations in the concrete of the compressed zone with the simultaneous achievement of the fluidity limit in the working reinforcement. The second case is the destruction due to the achievement of limiting deformations in the concrete of the compressed zone without reaching the fluidity limit in the working reinforcement. Both cases of calculation are reduced to one functional dependence. This avoids the delimitation of different calculation cases. The main no dimensional modifier is the mechanical coefficient of reinforcement. According to the developed method, examples of calculations of reinforced concrete, fiber reinforced concrete elements and fiber concrete elements with longitudinal reinforcement are executed. The possibility of a spread variant design of reinforced concrete and fiber concrete elements is shown.