The scientific work is dedicated to the analysis of existing methods for calculating the total value of concrete deformation under the simultaneous influence of mechanical load and elevated temperatures. During the operation of buildings and structures, it has been proven that the influence of temperature loads, especially in combination with force loads, leads to a significant change in the operational qualities of both individual structural elements and buildings as a whole. The relationship between stress, deformation and temperature of materials should be clearly defined during research of the structures operation under the influence of high temperatures. A so-called “rheological approach” is used to account for these interrelated effects, and the related effects between stress and expansion behavior are taken into account by introducing load-induced thermal strain into the calculation. In the conducted analysis, the results of experimental studies of foreign scientists and normative values, given in EC2 and ENV-1992, were taken into account. It was established that the distribution of stresses and deformations in concrete structures cannot be correctly determined exclusively by applying the corresponding recommended Eurocode 2 curves. Values of deformations, corresponding to compressive concrete strength at specified temperatures, are given without transparent justification of the way of taking into account the related effects between stress and expansion of the material. Thus, the σ-ε curves of concrete in EC2 should be used only for the heating phase, however, they are not used for the cooling phase. As further ways of improvement, on the basis of the existing EC2 methodology, the development of the mathematical “stress-strain-temperature” relationship is proposed for the research of interrelated effects between stress and expansion of concrete. To account for the interrelated effects between stress and expansion in concrete subjected to simultaneous heating and loading, an equation is proposed to calculate the strain value, corresponding to the compressive strength. Keywords: stress-strain state, concrete, temperature, calculation, analysis.
The article considers the issues of variant design of bearing elements of monolithic reinforced concrete crossbarless frame. In particular, the columns, in order to ensure increased reliability of operation of the frame in cases of exposure to various adverse conditions. Such conditions include factors of disproportionate destruction (progressive collapse), which can significantly damage the building. With variant reinforcement of columns, it is possible to achieve a state when the reliability of safe operation of the building will be most pronounced, which may be a recommended measure in the design of multi-storey buildings. It is noted that a rational increase in the reinforcement of columns on the lower floors leads to an increase in the parameter of trouble-free operation of the entire building in emergencies, and this is a sign of increasing the reliability of the entire designed frame of the building. The technology of estimating the reliability parameters is that along the height of the column there are four to five sections with a certain percentage of reinforcement, the maximum percentage (up to 2% -3.5%) is located in the lower zone of the columns, and the smallest % -1.0%) at the top of the columns. This armature is appointed proceeding from statistical calculation of a skeleton and the received internal efforts of M, N, V. In the resulted article as the device of calculation of a 14-storeyed with a cellar of a inhabited frame building the software and computer complex "SCAD" version 21.1.9.5 is used. The emergency situation is predicted in the form of an explosion in the basement of a residential building, which led to the destruction of three columns of the corner of the building and one stiffness diaphragm. Five possible options for column reinforcement were compared (there are 585 columns in the frame of the building). In the first and second embodiments, the reinforcement of the lower two zones was ϻ = 1.57%, the upper two zones ϻ = 0.5%, in the third variant, the reinforcement of the lower two zones was ϻ = 2.57%. In the fourth and fifth variants, the lower two zones had reinforcement ϻ = 1.0%, the upper two zones ϻ = 1.57%. In each of the variants the strength of the concrete changed: for the I and IV variants it corresponded to class C20 / 25; for II, III and V variants the concrete class corresponded to C32 / 40. The parameter of failure-free operation P (t) for the frame in each case was determined by the method of Kudzis AP The calculations showed that the values of P (t) for each option were: I - 0,978; II - 0.986; III - 0.998; IV - 0.969; V - 0.983. Thus, the most effective was the third option (maximum reinforcement of the lower tiers of the columns), which is recommended for implementation in the actual design. Keywords: disproportionate destruction, reliability and safety of operation, reliability indicators, reinforced concrete monolithic framework, variant reinforcement, efficiency of the accepted decisions.
Gradient damage models can be acknowledged as a unified framework of dynamic brittle fracture. As a phase-field approach to fracture, they are gaining popularity over the last few years in the computational mechanics community. This paper concentrates on a better understanding of these models. We will highlight their properties during the initiation and propagation phases of defect evolution. The variational ingredients of the dynamic gradient damage model are recalled. Temporal discretization based on the Newmark- $$\beta $$ scheme is performed. Several energy release rates in gradient damage models are introduced to bridge the link from damage to fracture. An antiplane tearing numerical experiment is considered. It is found that the phase-field crack tip is governed by the asymptotic Griffith’s law. In the absence of unstable crack propagation, the dynamic gradient damage model converges to the quasi-static one. The defect evolution is in quantitative accordance with the linear elastic fracture mechanics predictions. These numerical experiments provide a justification of the dynamic gradient damage model along with its current implementation, when it is used as a phase-field model for complex real-world dynamic fracture problems.
Some dynamic processes in pulsed discharge in combined hollow cathode used as source for analytical GD TOFMS are considered. The effect of the addition of hydrogen to glow discharge coupled to a time of flight mass spectrometer has been studied. Addition of hydrogen has shown the increase intensities of sample components and decrease intensities of discharge gas components. Reactions describing processes at presence of hydrogen are considered. Influence of pressure on discharge gas and dynamic of clusters transportation on intensities of clusters components was investigated for some types of clusters. Dynamic discrimination has allowed to increases number of determined elements due to essential reduction of interferences. 1. LOW TEMPERATURE PLASMAS 1. 1. PLASMA APPLICATIONS AND DEVICES Some types of glow discharge are used as sources coupled with mass-spectrometry for solid, bulk samples analysis and thin-layer determinations. These sources work with direct current (DC), magnetron, radiofrequency (RF) and pulsed discharges. High sputtering and ionization efficiency for pulsed discharge increase sensitivity, asymmetric origin of analyte and discharge gas ions allowing reduce background gas contribution, perturbation of chemical system, followed by different relaxation effects – for example dissociation and recombination of different molecular ions in afterglow, selective reactions between molecular ions and Hydrogen etc. These effects can be used in analytical GD TOFMS system for effective background discrimination. Besides pulsed glow discharge reduce average of discharge power and cathode temperature under high pulsed power. Pulsed discharge in combined hollow cathode (CHC) (see
Abstract Ce papier présente une simulation numérique 3D avec le code de dynamique rapide EUROPLEXUS de la dépressurisation rapide du réacteur HDR (accident de type APRP) où le phénomène de l'interaction fluide-structure est modélisé dans toute sa généralité. Les différents modèles de couplage fluide-structure disponibles dans le code sont rappelés brièvement. La modélisation EUROPLEXUS de l'essai V32 de la campagne HDR est présentée ainsi que les résultats numériques que l'on compare avec les mesures expérimentales. This paper presents a 3D numerical simulation with the fast dynamics software EUROPLEXUS of the depressurisation of the HDR reactor (LOCA type accident) where the phenomenon of fluid-structure interaction is modelled in a general manner. Different models of fluid-structure coupling available in the code are briefly described. EUROPLEXUS model of the test V32 of the HDR test campaign is presented as well as the numerical results compared with experimental measures. Keywords: dynamique rapidesimulation numériqueinteraction fluide structuredépressurisation du réacteur HDRcomparaison calcul essaiKeywords: fast dynamicsnumerical simulationfluid structure interactiondepressurisation of HDR reactorcalculation measurement comparison
The article considers the issues of variant design of bearing elements of monolithic reinforced concrete crossbarless frame. In particular, the columns, in order to ensure increased reliability of operation of the frame in cases of exposure to various adverse conditions. Such conditions include factors of disproportionate destruction (progressive collapse), which can significantly damage the building. With variant reinforcement of columns, it is possible to achieve a state when the reliability of safe operation of the building will be most pronounced, which may be a recommended measure in the design of multi-storey buildings. It is noted that a rational increase in the reinforcement of columns on the lower floors leads to an increase in the parameter of trouble-free operation of the entire building in emergencies, and this is a sign of increasing the reliability of the entire designed frame of the building.
The technology of estimating the reliability parameters is that along the height of the column there are four to five sections with a certain percentage of reinforcement, the maximum percentage (up to 2% -3.5%) is located in the lower zone of the columns, and the smallest % -1.0%) at the top of the columns. This armature is appointed proceeding from statistical calculation of a skeleton and the received internal efforts of M, N, V. In the resulted article as the device of calculation of a 14-storeyed with a cellar of a inhabited frame building the software and computer complex SCAD version 21.1.9.5 is used. The emergency situation is predicted in the form of an explosion in the basement of a residential building, which led to the destruction of three columns of the corner of the building and one stiffness diaphragm. Five possible options for column reinforcement were compared (there are 585 columns in the frame of the building). In the first and second embodiments, the reinforcement of the lower two zones was ϻ = 1.57%, the upper two zones ϻ = 0.5%, in the third variant, the reinforcement of the lower two zones was ϻ = 2.57%. In the fourth and fifth variants, the lower two zones had reinforcement ϻ = 1.0%, the upper two zones ϻ = 1.57%.
In each of the variants the strength of the concrete changed: for the I and IV variants it corresponded to class C20 / 25; for II, III and V variants the concrete class corresponded to C32 / 40. The parameter of failure-free operation P (t) for the frame in each case was determined by the method of Kudzis AP The calculations showed that the values of P (t) for each option were: I - 0,978; II - 0.986; III - 0.998; IV - 0.969; V - 0.983. Thus, the most effective was the third option (maximum reinforcement of the lower tiers of the columns), which is recommended for implementation in the actual design.
