Assessment of load-carrying capacity of metal and reinforced concrete railway bridges of different length built in 1930 - 2007, operated under modern heavy-weight trains, is considered in the ...article. To understand and cause the occurrence of deformations in structural elements, it is necessary to analyze the operation of bridge spans under conditions of increasing axial loads and traffic speeds. Deformation processes cause the appearance of defects, structural failures and accidents, which leads to material and environmental damage. The funds spent on bridge serviceability reconstruction are much more than those invested in protective measures. The main task is to study the interaction of bridges and rolling stock (bridge-train system), namely, the greatest influence from dynamic deformations and movements. The purpose of this work is to study the possibility of making way for heavy-weight rolling stock over the bridge spans. The research is based on the study of their load-carrying capacity estimation by test and classification methods. The paper presents the results of the measurements of the stress-strain state of bridge structures, obtained by the authors, using strain-measuring hardware-software complex (SMHSC). Depending on the results obtained, the decisions on the possibility of making way for heavy rolling stock with the axle load of 245-275 kN on the metal and reinforced concrete bridge spans are made.
Obtaining predictable characteristics for complex-geometry products made from dissimilar-material powder compositions used for lost-wax molding allows substantially expanding the applicability of ...special investment-casting methods. It has been established that no distribution of properties over the finished product is achieved when molding complex-shape compacts from a mixture of waxy and water-soluble components. The problem of elastic response of the compacted material of such nature is solved by means of a material experiment which allows for determining the influence of the initial packing and compaction parameters of spherical waxy elements on the stress-strain state of the compact. The paper presents the research findings in the form of empirical third order polynomial of stress-strain relations in powder bodies, considering various cases of positioning of deformable plastic and elastic elements.
The article deals with the issues of modeling the stress-strain state of the attachment points of the cab of a wheeled chassis of high load capacity. The main design loads are determined. Geometric ...and computational finite element models are constructed, taking into account the features of the metal structure. The technique of gluing elements of the grid model is applied. The contact interaction of the parts is taken into account. Based on the calculations performed, conclusions are drawn about the compliance of the developed structure with the strength requirements.
In this paper, a mathematical model of a multilayer panel made of nanomodified carbon fiber reinforced plastic with asymmetric packing is proposed. The introduction of nanosized particles into the ...composition of the composite or its components (fiber or binder) allows not only to increase its physical and mechanical properties, but also to improve the picture of the residual stress-strain state. The paper investigates the effect of nanomodification of carbon fiber reinforced plastic on the residual stress-strain state after molding using numerical and analytical methods. Numerous results of computational experiments have been obtained. The results of numerical and analytical modeling are compared with experimental data. Conclusions are drawn about the possibility of reducing the residual stress-strain state in structures with asymmetric reinforcement schemes when using a matrix containing carbon nanoparticles. A mathematical model of a multilayer panel made of nano-modified carbon fiber with asymmetric packing has been built. Investigation of the residual stress-strain state of structural elements made of carbon fiber reinforced plastic made it possible to reveal the possibility of reducing the residual stress-strain state and leash in structures with asymmetric reinforcement schemes when using a matrix containing carbon nanoparticles.
Purpose is to study influence of a longwall face advance on the geomechanical situation in the neighbourhood of a mining site based upon determination of changes in standard and critical subsidence ...of the immediate roof rocks. Methods. To study a geomechanical situation in the neighbourhood of a mining site the authors have applied software product GeoDenamics Lite developed at Dnipro University of Technology. The software product relies upon a calculation procedure of stress-strain state of rocks by Professor O.V. Savostianov. Expediency of the software selection is based upon the supported control and adaptation of a coal mining technique to changes in geodynamic stress fields in the anisotropic rock-coal medium impacting temporal and spatial changes in the technological parameters. Findings. The basic problems have been singled out connected with certain changes in a longwall face advance. For the first time, an analytical scheme of tangential stresses within the immediate roof rocks has been developed for Lisova mine of SE Lvivvuhillia under the conditions of coal seam mining by means of the paired longwalls which makes it possible to determine both physical and geometrical parameters of standard loads within the formation. Originality. Dependencies of temporal and spatial changes in subsidences and horizontal displacements of rock layers of the immediate roof have been defined being 5.2 m for the upper rock pack and 3.9 m for the lower pack if the longwall longwall face advance is 1.9 up to 4.8 m/day. Both physical and geometrical parameters of the reference pressure have been defined as well as the parameters of lower sandstone pack in the process of the main roof subsidence. Impact of the extra pressure forces on the immediate roof rocks has been analyzed at the moment of critical lowerings of the immediate roof rocks. In this context, standard loading from the overlying formation in addition to tangential stresses in the roof result in rock failure due to vertical cracks above a longwall face. Practical implications. The engineering methods have been developed making it possible to identify impact parameters of a longwall face advance on the geomechanical situation in the neighbourhood of a mining site. In future, it will help forecast changes in the reference pressure around a longwall face while preventing emergency settlement of the powered support.
This article is devoted to the stress-strain state (SSS) study of metal and reinforced fiber-reinforced concrete beam under static and shock loading, depending on the bimodularity of the material, ...the mass of the beam, and the location of the reinforcing bars in zones under tension and compression. It is known that many materials have different tensile and compression properties, but in most cases, this is not taken into account. The calculations were carried out by using load-bearing metal beams made of silumin and steel and reinforced concrete beams under the action of a concentrated force applied in the middle of the span. The impact load is considered as the plastic action of an absolutely rigid body on the elastic system, taking into account the hypothesis of proportionality of the dynamic and static characteristics of the stress-strain state of the body. The dependences of the maximum dynamic normal stresses on the number of locations of reinforcing bars in zones under tension and compression, the bimodularity of the material, and the reduced mass of the beam are obtained. A numerical study of SSS for metal and concrete beams has shown that bimodularity allows the prediction of beam deflections and normal stresses more accurately.
he article deals with the influnce of longitudinal reinforcement of the support zone of reinforced concrete slabs on the strength and crack resistance under the criterion for punching failure. The ...evaluation of impact was carried out by the method of numerical studies based on finite-elementcomputational technologies. The results of physical experiments published in the scientificliterature are taken as the basis for the conducted research. The existing provisions of the existing domestic and foreign standards for the calculation of slab reinforced concrete structures according to the criterion for punching failure are considered. The main provisions of the applied finit element approach are presented, verificationis performed and the correctness of the applied technique is justified In the numerical studies, the forecast of strength and crack resistance was done for considered reinforced concrete slab structures; the results of numerical studies were compared with the data from physical experiments and the evaluation results based on the relevant domestic and foreign regulations. According to numerical studies results it was stated that longitudinal reinforcement of the tensile zone of slab structure has a significantimpact on both the level of load-bearing capacity and the scheme of crack formation and propagation. The results of the implemented studies justify the necessity to revise the national standards of structural analysis for reinforcement concrete slab structures under the criterion for punching failure.
The method of calculating wooden obliquely bent beams using the deformation model has been developed. This technique considers the distribution of stresses in the compressed and stretched zones of ...the calculated section of the beam, including the formation of folds in the compressed zone of pure bending. It was established that the current norms for calculating wooden structures provide a significant margin of strength compared with the calculation based on the deformation model: for the angle of inclination 100 - by 2.49 times, for the angle of inclination 250 - by 2.15 times. the maximum bending moment that the beam can absorb, determined by the deformation model at the angle of inclination 100, is M=18.72 kNm, for the angle of inclination 250– M=17.1 kNm, which differs by 8.2% and 3.3% from the experimental data for similar beams at the corresponding angles of inclination. An example of calculating a wooden glulam beam under oblique bending according to the newly developed method is given.
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