Materials Science Forum Vol. 968

Abstract: The article is devoted to the investigation of the influence of columns’ concrete body destruction size on the bearing capacity of building structures. The joint spatial work of steel strengthening structures with reinforced concrete constructions is investigated. The results of numerical modeling the stress-strain state of damaged reinforced concrete columns in the middle row of the industrial building are presented. The numerical modeling was executed in the system NASTRAN. It was carried out the numerical calculation of reinforced concrete column in the middle row without damages. Then it was modeled the column damage in form of a "downed" concrete angle to a depth of 50, 100 and 200 mm and denudation of bearing longitudinal armature at length of 1000 mm from supporting part of the column. In this case two separate models were investigated - with the location of damage from the compressed or extended side of the column. The conclusions about feasibility of columns strengthening by steel clip are made.

Abstract: This article is devoted to the analysis of one of the most common structural designs of the steel frame of small spans, currently used in India in construction and reconstruction for seismic areas. This scheme constructively involves the implementation of the main bearing elements - bolts and columns - in the form of a spatial truss box section. At the same time, rather simple rolling profiles from small-sized corners are used, as well as a round steel bar. The studies performed by the authors were carried out using the finite element method based on the national design computing complex SCAD for Windows. The loads, as well as the geometrical characteristics of the profiles, were taken according to the current building standards of India. Based on the results of the analysis, a number of recommendations were formulated to improve the efficiency of the considered design scheme for seismic effects of varying intensity.

Abstract: The paper presents experimental and computer researches of ferroconcrete beams at high-temperature influences. There were conducted the experimental fire tests of ferroconcrete beams. The most promising way of verifying these experimental research data is computer simulation of structures, also during a fire. In order to evaluate the quality of the experiment and the reliability of the received temperature distribution, there was conducted a computer simulation of the ferroconcrete beam in the ANSYS R.17.1 software complex. There were conducted a comparative analysis of the results of experimental studies and numerical analysis. The results confirm that the method of conducted experimental research and computer simulation with further numerical analysis can be recommended for practical application.

Abstract: The unsatisfactory technical condition of many buildings and structures is due to their aging and requires a quick technical condition assessment. The most promising way for experimental researches data verification is computer modeling of structures, also during a fire. It is advisable to use the ANSYS software. Experimental fire tests of reinforced concrete slabs were carried out. In order to assess the experiment quality and the reliability of the received temperature distribution data, it was used a reinforced concrete slab computer simulation in the ANSYS R.17.1 software system. There was provided a comparative analysis of experimental studies results and numerical data analysis. The results confirm that method of conducted experimental research and computer simulation with further numerical analysis can be recommended for practical application. The mathematical model makes possible operative prediction for the controlled parameters values of building structures.

Abstract: The article deals with theoretical and experimental research into dependency of crack resistance of concrete under dynamic effects on coefficients of grain separation of coarse and fine aggregates. It was established that these dependencies were of extreme nature. The research yielded the optimal values of coefficients of grain separation of coarse and fine aggregates, cement particles, and also water-to-cement ratio for the materials under study; these factors provided the best physical and mechanical properties of concrete, including its crack resistance under dynamic effects, both impacts and vibrations..

Abstract: Direct dynamic analysis of reinforced concrete frame buildings taking into account the nonlinear and plastic properties of materials by the finite element method is connected with the solution of a system of solving equations of very high order. This is due to the fact that it is necessary to split the beams and columns that form the structure into a large number of finite elements, since the deformation properties of concrete are different in the compressed and stretched zones, as well as in the loading and unloading zones. In this paper, we propose a method for investigating nonlinear spatial oscillations of a flat reinforced concrete frame, based on the method of boundary elements, which leads to a much smaller amount of computational work.

Abstract: An axisymmetric contact problem concerning the torsion of a circular shaft of an orthotropic-nonhomogeneous half-space is considered. By means of the technique of integral transformations of Laplace and Hankel, with the subsequent application of the orthogonal polynomial method, an approximate solution in the transformant space is constructed. Also was performed reverse transformation. Calculated formulas for the angle of rotation of the shaft and the tangential stress acting on the contact area are obtained. Numerical calculations for certain types of heterogeneity have been performed. Comparison of the obtained results with the previously known results is made.

Abstract: Specified calculation of steady-state oscillations of circular transtropy plates of medium thickness was performed. The calculation considers transverse displacement deformation and transverse compression effect. Compared to other plate models, such clarifications highly increase calculation accuracy of their stress-strain state. While considering the influence of tangential loads and inertia forces, they do not change equations structure nor increase their order. Obtained equations deal with specification via certain parameters, which depend on characteristics of plate anisotropy and geometry. The calculation order of the equations remains the same, stresses and forces stay similar as in other plate models. At the same time, their accuracy highly increases and becomes close to the results of elasticity theory spatial problem. In case of hinged round plate, the solutions for the free oscillation frequencies are found. Obtained numeric results are compared with corresponding results of classic theory of Kirchhoff’s thin plates. On the basis of these comparisons, the conclusions about significant influence of transverse displacement and compression effects on the magnitude of oscillation frequencies in the direction of their significant decrease are made. This effect is especially noticeable at low transverse physical characteristics of the plate. This conclusion coincides with corresponding results, which were obtained in the monograph of V.T. Grinchenko for a thick plate in a spatial setting.

Abstract: A spatial problem of the theory of elasticity for the layer with an infinite round cylindrical inclusion is investigated. At the boundaries of the layer, displacements are given. The cylindrical elastic inclusion is rigidly coupled with the layer and their boundary surfaces do not intersect. The solution to the spatial problem is obtained by the generalized Fourier method, with regard to the Lamé system of equations. The obtained infinite systems of linear algebraic equations are solved by a reduction method. As a result, the values ​​of displacements and stresses in the elastic body are determined. A comparative analysis of the stress state for different geometrical parameters is carried out, and a comparison is made with the stress state in the layer with a cylindrical cavity.

Abstract: The effect of the polyharmonic external excitation causes the emergence or onset of novel properties in the system. The article devoted into the oscillations induced in a rigid system by the polyharmonic external excitation. The analysis of the results obtained in this research confirms that the systems with the nonlinear elastic characteristics are rather sensitive to the changes introduced into the external excitation according to the law. Therefore, some assumptions, for instance, those concerning the monoharmonic nature of changes in the external excitation, which are commonly used in studying the real mechanical systems, are not always correct.