"Вестник МГСУ"

Multilayer exterior walls are wide-spread in modern civil construction. One type of such structures is a three-layer wall with insulation layer made of lightweight concrete and exterior layers made of structural concrete. It is necessary to provide durable monolithic connection of concrete layers in the process of manufacturing this structure in order to decrease the percentage of web reinforcement and increase thermal engineering homogeneity of multilayer exterior walls. Experimental research of three-layer samples with external layers made of claydite-concrete and internal layer made of polystyrene concrete were conducted in order to establish the strength of layer connections in the multilayer exterior wall. Different temporal parameters and concrete strength were assigned during manufacturing of the samples. The samples were tested under axial tension and shear in the layer contact zone. The nature of tensile rupture and shearing failure was checked after the tests. The relations between manufacturing parameters, strength of the concrete used in samples and layer connection strength were established as a result of experimental research. The climatic tests of three-layer exterior wall model made of claydite-concrete and polystyrene concrete were conducted in order to establish the reduction of the layers contact zone strength during the maintenance. The wall model was made of concrete samples of varying strength. The experimental model was exposed to 35 cycles of alternate freezing and thawing in climatic chamber. During freezing and thawing, the strength tests of external and internal layers contact zone by tearing the cylindrical samples were conducted. Consequently, the nature of contact zone strength reduction for the samples with different concrete strength of external and internal layers was established. As a result of the conducted research, the optimal temporal parameters of manufacturing and optimal concrete strength were established. It is recommended to use these parameters in the process of manufacturing multilayer concrete exterior walls in order to provide durability of the concrete layers monolithic connection during maintenance of the structure.

The article describes the calculation of plates on the elastic basis, both two-layer and single-layer. The calculation is based on the solution of the differential equation of bending plate by finite difference method. The calculation results are compared with the numerical solution in the program complex. The percentage of differences of values depending on the method of division or method of solving is shown. We considered a problem when a foundation plate and a construction are plates, which are deformed together, that, in fact, corresponds to the problem of bending a two-layer plate on elastic basis. In case of a two-layer plate in order to find the solution of the problem we need to solve the equation of bending of plates that are structurally similar to the traditional, but still give different results. In solving finite difference operators derivatives are substituted into differential equation which must be in accordance with each grid point, as well as at the border. If we consider the problem in the conventional formulation, only the lower layer is bended in the plate; the analysis of the plate, which takes into account the weight of its own layers, both layers are deformed together. Also when considering a two-layer plate, the neutral layer is deposed away from the upper layer, consequently, the whole foundation plate may be in the condition of stretching. When comparing the results of analytical and numerical calculations of the values obtained in general there are little discrepancies. Thus, there is the possibility of holding combined calculation of the “structure-foundation-base system” by finite difference method using a two-layer model of a plate on elastic basis.

In the paper the author presents the results of calculations of the system «structurefoundation-base» in case of using the two-layer and the single-layer beam models on an elastic basis with variable and constant coefficients of subgrade reaction. The analytical solution is obtained using the method of initial parameters. The calculations are carried out in case of building up the structure.The method of calculating two-layer beam with variable flexural rigidity along the length on an elastic foundation was described in the author’s previous articles, while in the present paper variable coefficients of subgrade reaction are taken into account. A two-layer beam is a beam of variable rigidity, the lower layer simulates the foundation, and the upper — the structure, at the same time the weight of each layer is considered.For comparison, the problem is also considered in its traditional statement. That means the problem of single-layer beam bending is solved with cross-section of constant length, which is freely lying on an elastic basis of Winkler’s type.The results of calculations of two-layer and single-layer beams show, that the values of the internal forces and stresses are higher with variable coefficient of subgrade reaction than with the constant one. When comparing the two-layer and the single-layer beam models with the same foundation characteristics, the values of internal forces in two-layer beams are much higher.On the basis of the calculations we can make the following conclusion: in order to obtain more reliable prognosis of the stress-strain state of the system «structure-foundation» on an elastic basis, it is appropriate to carry out calculations with the use of a contact model in the form of a two-layer beam on an elastic basis of Winkler’s type with variable coefficients of subgrade reaction. The model allows us to take account of such factors as rigidity changes in the base and the rigidity of the upper structure.

In the paper, the authors provide the results of analysis of a real construction facility performed with the help of a model of a two-layer beam of variable rigidity resting on the elastic bedding. The bottom layer of a two-layer beam simulates the foundation, the upper payer stands for the structure, and the weight of each layer is taken into consideration. The characteristics of the upper layer change alongside its length. Analytical and numerical methods of calculation were applied to solve this problem.
The analytical solution is based on the method of initial parameters and backed by the practical data extracted from "Frame and Towerlike Buildings: Mattress Foundation Design Manual". According to the above manual, whenever the length-to-width ratio of a building exceeds 1.5, one-dimensional pattern composed of a composite beam resting on the elastic bedding may be used. The beam is divided into several sections, and deflection of each section is identified. It is equal to the settlements of the bedding surface. The rigidity change alongside the length of each section is assumed to be permanent, i.e. the beam is considered as the one that demonstrates its piecewise-constant rigidity.
The following conclusion can be made on the basis of the calculations performed by the authors: the calculation of the «structure-foundation-bedding» system may require a simplified model representing composite beams and plates resting on the elastic bedding. More accurate models, such as sets of finite elements, are recommend for use in conjunction with simplified ones.

Introduction. When building residential, public and administrative buildings of various spatial structural designs (monolithic, precast-monolithic, precast, etc.), it is common practice to design self-sustaining (non-structural) outer walls within a storey. Developing and using new design and fabrication solutions of multilayer industrial-made wall panels in modern construction practice makes actual the issue of improving methods of their calculation in different stages of maintenance and under various sorts and combinations of loads and effects. However, there is an infinite variety of possible loading levels in practice and, therefore, the same variety of design approaches would be required. This is obviously unacceptable for engineering calculations, hence it is necessary to provide a monolithic matrix bond of layers, both technologically and structurally, which can provide a generalized approach to the calculation of multilayer enclosing structures in accordance with current design standards. Materials and methods. The article describes structural features of a multilayer wall panel made of structural concrete with the middle layer of concrete with low thermal conductivity and monolithic bond of layers. These features have an influence on creation of a design model and a calculation procedure in the stages of transportation, installation and maintenance. Results. The article has examined the structures described above in the sense of design parameters that provide their competitive advantages in strength and maintenance as compared with conventional mass-built enclosures. Conclusions. The studies demonstrate that when combining loads of force and non-force character, stresses in the considered structure do not exceed allowable values in all the stages what proves the prospects of using the multilayer panels with monolithic bond of layers for erection of various-purpose frame-panel buildings.