Key Engineering Materials Vol. 828

Abstract: To protect civil buildings, industrial facilities and bridges against earthquakes and explosions, various seismic isolation systems (SIS) are used. SISs always include dissipative elements that dissipate energy transmitted to the protected object (PO) during seismic effect, operation of which is based on the elastic-plastic deformation of special structures — elastic-plastic dampers (PD). The paper proposes a method for selecting the optimum design parameters of elastic-plastic dampers in SISs. The problem is solved upon specifying an ensemble of random seismic effects. A suite of artificial accelerograms obtained by statistical modeling is used as a stream of events supplied to the right side of motion equations. Dispersion of PO absolute accelerations was chosen as an optimization criterion. After linearization of the model, the dimensionless damping coefficient introduced into the dynamic model according to the Voigt–Bock hypothesis was taken as a variable parameter. Relationship between the selected optimization criterion and the theory of seismic risk of V.V. Bolotin has been established. It is shown that optimization of the damping coefficient reduces the seismic risk by 1.5–1.8 times. A method has been developed for transition from the optimum damping coefficient to design parameters of elastic-plastic dampers that implement this coefficient. Analytical dependences have been obtained enabling to set those parameters easily.

Abstract: This paper presents a new method and toolset to measure strain values of the fabrics under biaxial tensile test. The proposed model is based on the reverse engineering of Delta 3D printing system. A comparison is made to the existing widely accepted models of strain measurements. The designed toolset was developed by parameter based modelling and genetic optimization to ensure that the equipment can function within the given strain domains. The equipment design model can be adapted to any biaxial tension frame.

Abstract: The territory of Armenia is characterized by a wide variety of volcanic natural porous rocks with extremely rich natural resources. Tuff stone is one the varieties and is traditionally used as a masonry material, and waste, estimated at millions of cubic meters has accumulated near the mining areas and it’s disposal is an important environmental issue. Slag and pumice stones, as well as some types of tuffs, are used as aggregates for general-construction lightweight concretes, and as heat insulating backfills, etc. Since the 1980s, we have begun systematized scientific studies to identify the natural potential and the most optimal branches for the use of these rocks, where it is possible to obtain the maximum technical and economic benefits through the targeted use of their specific natural properties. Taking into account the conditions of these rock formation, as well as the high prices available on the world market and the demand for lightweight, heat-resistant insulating concrete, first of all, by complex, versatile studies, they are classified by high-temperature properties, technical capabilities and specificity of using some varieties as aggregates for lightweight heat-resistant concrete, with application temperature up to 800...1100°C. It is shown that, compared with the expensive artificial porous heat-resistant aggregates widely used in practice, these rocks are out of concurrence, as the corresponding compositions, porosity of the structure and high-temperature processing were obtained in natural conditions, due to which they do not require manufacturing costs for particular components and high-temperature processing and in the natural form are ready to be used in this area. Along with this, some of them also have high acid resistance and are suitable for use in the most valuable concretes with the simultaneous triple effect of lightness, heat resistance and acid resistance.

Abstract: On the base of volcanic glass - perlite, the energy-efficient technology of cellular glass for heat-insulating purposes has been developed. Compositions of nanosized modifier and redox gas formers were developed by the method of experimental-statistical modeling and optimization of probability parameters, allowing to obtain cellular glasses with low average density and almost closed porosity in a single technological process at technologically acceptable temperatures. In the production of cellular glasses (foam glass) of new generation, based on natural glassy rocks of silicate and aluminosilicate composition modified with sodium hydroxide, in the presence of water and gas-forming additives, during mixing and sintering, the components react at the nanoscale level to form glass under low softening temperature and sufficient quantity of foam stabilizers. The main scientific results - the use of nanotechnological modification of amorphous silicate and aluminosilicate rocks in the technology of cellular glass for construction and technical purposes, the development of compositions and method for the production of cellular glass using energy-saving technology with the following performance parameters: average density of 115...250kg/m³, coefficient of thermal conductivity 0,051...0.075W/(m•K), water absorption 1.6...4.0%, compressive strength 0.14...4.20 MPa, hydrolytic glass class I...III.

Abstract: The features of the structures of complex monolithic reinforced concrete structures are given, the necessity of their organizational and technological design to ensure quality, reduce the duration and safety of construction and installation works is substantiated. A fragment of the formwork for complex curvilinear beams is presented, where the permanent and temporary loads, the permitted steps of the main and secondary beams and remote scaffolds for the PERI and CRAMOS modular formwork systems, which are more common in RA, are calculated in detail.

Abstract: The milling cutter obtained from milling the surface layers from the worn out class A, S and GP roads is a valuable component of the newly produced asphalt mixtures. The proportion of granulate as a material obtained from the aggregate cutter with the content of used asphalt binder for MMA production according to available recommended documents should not exceed 30% of recycled material in the overall composition of the weight formula of the new mixture designed with the participation of fresh native aggregates. MMA properties with a 30% share of the milling cutter for fabrication of the foundation layer and an intermediate layer with parameters do not differ from mixtures made of native aggregates. It is purposeful to develop framework standards for specifying the methods of obtaining and its classification for objective evaluation and a high-value application in MMA technology involving partial or full processing of an asphalt cutter.

Abstract: The article describes the features of the effect of corrosion of reinforcement on the bearing capacity of reinforced concrete columns in a "standard" fire. On the basis of the standard calculation method, the fire resistance of the column was estimated under a four-sided fire effect taking into account the different duration of the fire. The study examined the operation of the column in a corrosive environment, it was assumed that the initiation of corrosion of concrete and reinforcement will occur after 10 years of exploitation. It was found that the destruction of concrete protective layer 25 mm thick in a medium aggressive environment will occur after 25 years, and the diameter of the reinforcement during this period will decrease by 20%. To compare the results, a reinforced concrete column with a section of 400x400mm was calculated under the influence of a “standard” fire under normal operating conditions and taking into account work in a corrosive environment. The results of heat engineering calculations are presented, where the temperature changes in the reinforcement depending on the heating time and reduction of the protective layer thickness, as well as the change in the diameter of the reinforcement and its effect on the bearing capacity are shown. It has been established that reducing the cross-sectional area of the working reinforcement and reducing the cross-sectional dimensions of the column due to the occurring corrosion processes leads to a decrease in the fire resistance limit on the loss of bearing capacity by 58%.

Abstract: Taking the standard sand of Fujian as the test material, this paper concentrates on studying the influence of different stress increment directions on the direction of plastic strain increment of sand materials under different stress states and the underlying mechanism. The test results show that the plastic strain increment angle rotates counterclockwise with the increase of stress increment direction angle, but the two angles do not coincide; the higher the stress state parameters is, the larger the stress increment direction angle range corresponding to sand dilatation is, the smaller the plastic strain increment direction angle range is, and the plastic volumetric strain still increases in critical state.The plastic flow mechanism of sand is explained from the average stress increment, generalized shear stress increment and stress state, which may provide theoretical reference and numerical support for the related research of plastic strain increment direction of sand.

Abstract: The paper discusses the process of non-linear deformation of shell structures made of reinforced concrete. A mathematical model of deformation in the form of the functional of full potential deformation energy is provided. The model is based on the Kirchhoff–Love hypotheses, and allows accounting for structure reinforcement with stiffeners. An orthogonal network of stiffeners, located from the concave side, is considered as the structure support. Type of load — external, uniformly distributed. The Ritz method is applied to the functional to reduce the variational problem of the functional minimum to a system of nonlinear algebraic equations. Then, for each load value, the problem is solved using iterative methods. Analysis of strength and stability of shallow shells of double curvature and rectangular planform is performed. Values of critical loads, deflection and stress fields are obtained. Curves of deflection depending on load are provided. All results are given in dimensionless parameters. The Mohr–Coulomb criterion was used to analyze concrete strength, and the Lyapunov criterion was used for stability analysis. Influence of the number of stiffeners reinforcing the shell on the resulting stress values is shown. It has been revealed that with account for physical non-linearity of concrete, when the dependence of stresses and deformations is curvilinear, deformations (and deflections as well) of shells increase in comparison with the linear-elastic solution. It has been also found that when nonlinearity is taken into account, redistribution of stresses over the shell field occurs (the maximum stresses shift towards the shell contour).

Abstract: The purpose of the study is to establish accuracy of determining the load-bearing capacity of bored piles according to the method specified in Regulations 24.13330.2011 "Pile foundations". Relevance of the topic is determined by the following: the load-bearing capacity of a pile is a fundamental indicator affecting all subsequent activities related to foundation design, and accuracy of analytical solutions for complex engineering and geological conditions is highly questionable. Field tests of bored piles were carried out in engineering and geological conditions of Saint Petersburg with deformation modulus from 10 to 40 MPa at a load in the range from 1,000 to 6,300 kN, at achievement of absolute settlement of 40 mm. Piles with a diameter from 0.15 to 0.88 m and a length from 10 to 47 m were made using various technologies: using casing, using slurry, using a flight auger. Following the results of field tests, diagrams of load-bearing capacity of piles according to the material, depending on geometrical parameters and manufacturing techniques, diagrams of actual and designed load-bearing capacity of piles were plotted. Approximating functions to describe the dependences were obtained. According to the analysis of the results, it is possible to conclude that the load-bearing capacity of the bored pile during field tests is 1.4–1.7 times higher than the load-bearing capacity of the pile designed according to Regulations 24.13330.2011; the average share of the load-bearing capacity along the side surface of the pile was 65% and under the pile toe — 35%.