"Вестник МГСУ"

The article includes an analysis of the influence of the natural conditions of the region on the structural and stylistic features of Arab architecture. National architecture depends on the features of natural-climatic conditions of the region: geographical location (the climate, terrain, building materials), seismic activity, geological structure. The Muslim architecture was influenced by: high seismic activity; the lack of wood; dry and hot climate; high temperature drops in the daytime and at night. These are the peculiarities of Asia. The Arab countries are located in several climatic zones: in subtropical, the Northern tropical and subequatorial zones. The climate here is hot and arid. Forests grow only on some slopes. A significant part of Africa and Arabia is situated in the area of the desert. In Syria forests are found only on the Eastern slopes of the mountains. There are stunted coniferous and deciduous trees. These trees are thin, low and unsuitable for construction purposes. In Iran forests grow on the Northern slopes of the Mount Elbrus, at the altitudes of up to 2500 m, and on the coast of the Caspian Sea. The Central Iranian plateau has almost no vegetation. There is very little rainfall (100...250 mm per year). The air cools down quickly at night. There are also large diurnal and seasonal temperature changes. Rock formation is weathered therefore the sandy-clay deposits are formed. They are suitable for making bricks. The clay in the form of bricks was used as a building material. The unfired adobe was used too. It worked rather well in dry climatic conditions. The widespread use of the adobe influenced the color of the buildings - they were the color of soil. The wood as a construction material was scarce, so in large spans domes were built. Vaults and arches were built without the use of scaffolding and cradling. This influenced their shape. Wood is only used for architectural elements of palaces (rare wooden tall columns, ceilings and window grates made of wooden elements) and for construction of ceiling of traditional houses. Thin and uneven beams were unsuitable for the interior of the palaces.

The proportions of buildings, design and building materials in traditional Muslim architecture depended on geoecological factors of different regions of Islamic countries. One of those factors is a high seismicity site. It had the greatest influence on the appearance of monuments in the selected region. The influence of seismicity on the architecture of the buildings is considered in the article on the example of the architectural monuments of the Republic of Uzbekistan - madrasah of Ulugbek of the 15th century in Samarkand, the Kalyan mosque in Bukhara and the Syrian Umayyad mosque (708 buildings) in Damascus. The seismicity of the region is high. In order to determine the seismic resistance of architectural monuments the requirements SP 14.13330.2014 (the Current set of rules “Construction in seismic regions” (Seismic Building Design Code), revised edition of SNiP II-7-81*) and the Eurocode EN 1998-1 were used. On the basis of calculations tables comparing performance were made. The structural characteristics of monuments were compared with the characteristics required by the standards. The point value of seismicity of the territory which ensured the stability of the buildings was determined. Comparing the proportions of the monuments with Russian and European regulations on earthquake-resistant construction, we demonstrated the compliance of their architectural forms with the seismic activity of the area. Traditional architecture evolved from random search under the influence of the centuries of experience protecting the buildings from adverse natural influences. The design and shape of these ancient Muslim buildings, limited by the requirements of seismic resistance, has been subsequently reiterated in other structures, determining the style of Muslim architecture. The analysis allows us to see how the architects used the general principles of earthquake-resistant construction on different buildings. The destructions during earthquakes occurred only after structural deterioration of the materials, and were local in nature. Most of the buildings have symmetrical structure, the corresponding proportions in plan and in height, with using materials of sufficient “strength and elasticity”. The whole appearance of the buildings and the architectural style is not accidental. The proportions of the buildings - the height, width of span load-bearing structures, walls and openings, the symmetry of the buildings, domes, arches, windows, all structural dimensions were dictated by the requirements of seismic resistance.

The superelement of a column of rectangular section made of homogeneous material and intended for linear analysis, developed by authors earlier on the basis of the three-dimensional theory of elasticity, is updated with reference to static analysis of reinforced concrete columns with account for geometrical nonlinearity. In order to get the superelement the column is divided on sections and longwise into eight-node solid finite elements modelling the concrete and two nodes rod elements modelling reinforcement. The elements are connected with one another in the nodes of finite element mesh that provides joint operation of concrete and reinforcement. The internal nodes of the obtained finite element mesh are excluded at the stage of stiffness matrix and load vector of a column calculation. Formulas for calculation of linearized stiffness matrix of a superelement and a vector of the nodal forces statically equivalent to internal stresses are received. The element is adjusted to the computer program PRINS, and can be used for geometrically nonlinear analysis of complex structures containing reinforced concrete columns of rectangular section. Separately standing reinforced concrete column was calculated on longitudinal-transverse bending for the verification of the received superelement. The critical load was determined according to the results of calculation. The determined critical force value corresponds to the theoretical value. Thus, the proposed method of accounting for the geometric nonlinearity in the analysis of reinforced concrete columns can be recommended for practical use.

The method of localization of changes in the deflected mode is based on the analysis of time series of oscillations (displacement, velocity, acceleration) of building constructions and structures. The method is based on the hypothesis that any changes in the deflected mode of structures result in changes in the oscillation energy. In this case, once the information on the structure oscillation parameters in different points of the building is available, the changes in the oscillation energy will signify the changes in the deflected mode in the relevant points.

The superelement of the rectangular cross section column designed by the authors earlier for the linear analysis purposes is now applied to analyze the same column with account for the geometric nonlinearity. The superelement is composed of eight solid finite elements. The stiffness matrix technique, the initial stress matrix and the analysis of the vector of unbalanced nodal forces are described.The procedure for excluding internal degrees of freedom of a superelement, using the layer-by-layer reduction method, is described in detail. All calculation formulas are provided in the article. The element, developed by the authors, was adapted to PRINS finite element software; therefore, it can be used to perform the nonlinear analysis of building structures. The console beam, having a rectangular cross section, was analyzed in transverse longitudinal bending to verify the developed element. The comparison of the theory and calculations using PRINS software proved the accuracy of the proposed technique.

They cause mistakes in the transfer of forces in specific points and invariability of sizes and types of cross sections of rods in the course of their deformation. The approach to the analysis of rectangular section columns is proposed. The new approach originates from the three-dimensional theory supplemented by the superelement technology. The column is divided into sections and finite elements. The analysis of physically nonlinear structures is executed using the PRINS software. The flow theory is used to identify the characteristics of finite elements. Huber-Mises plasticity criterion is applied. The console beam loaded by concentrated forces on the free end is calculated to verify the element. The limiting load value identified by PRINS software complies with the theoretical values derived using the theory of limit equilibrium.

The author considers the key parameters used to monitor the condition of structures in the course of their long-term use. In the process of analyzing the expediency of employment of the parametric method of prognostication, the author identified the main parameters of structures made of different materials to be monitored for the above purpose. The research team led by the author systematized the key parameters of masonry, reinforced masonry, concrete, reinforced concrete and structural steel. Thus, the key parameters of reinforced concrete structures include displacement of supports, size reduction of the cross-section of a structural element, loading value, concrete strength in compression, tensile strength, cross sectional area of reinforcement, bearing capacity (for all sections), crack opening width (normal and oblique), deflections, and adhesion between concrete and reinforcement.Prognostication requires identification of the limit values of the above-mentioned parameters. Most of them are specified in the effective regulatory documents; some may be found in the reference and research literature. For example, any increase of corrosion in excess of 15% of the cross sectional area will not cause the failure of the structure. It is recommended to use the method of intervals as a most efficient one in the context of limited information. It contemplates development of interval boundaries of the most probable values of changing parameters. A general pattern for the prognostication of the remaining service life of building structures using the key parameters (the parametric method) may be used to identify initial values of these parameters and limits of changes in their values.

The theory of the strength of materials has produced a substantial influence on the development
and practical implementation of computer methods of the strength analysis of beams and
beam systems. Beams are modeled through the employment of one-dimensional elements within
the overwhelming majority of the finite element method software programmes; the stiffness matrix
is derived on the basis of the hypothesis of flat sections, and end forces concentrate in the centres
of the gravity of cross sections. This approach makes it possible to develop effective algorithms,
although it has several drawbacks. They include an incorrect transmission of forces from beams
to plates and massive elements of structures, difficulties in taking account of the warping effect of
the beam, and the complexity of taking account of physical and geometrical nonlinearities. Some
authors suggest using the three-dimensional theory with account for the flat sections hypothesis. It
encompasses the patterns of rotations of sections in the analysis of structures, although the problems
of warping and shear deformations remain.
The authors propose a new approach to rectangular column modeling by means of the finite
element analysis of building structures. Each column is presented as a set of three-dimensional
8-node elements with arbitrary discretization alongside the cross section and the height of the column.
The inner nodes of the finite element mesh are excluded sequentially layer by layer, thus,
reducing the stiffness matrix and other characteristics of the column with reference to its top and
bottom cross sections. The finite element method has been adapted to PRINS software programme.
The comparative analysis of the two structures has been completed with the help of this software.
The structures exposed to the structural analysis included slabs and columns. In one case,
columns were modeled with the help of one-dimensional elements, and in the another case, the
proposed elements were used. The comparison of the results demonstrates that the employment
of the proposed elements makes it possible to avoid problems associated with the transmission of
the force in a particular point.