Improving the efficiency of applying the method of slab and floor lifting

. C urrently, in relation to the problem of erecting buildings and structures using the method of lifting of slabs and floors, there is a need to evaluate the effectiveness of the organizational and technical solutions in the process of construction and assembly works. This publication reviews the process of construction and installation works by lifting the slabs and floors with an analysis of all the advantages of this method over others. It also reviews the factors that affect the effective use of this method. Basing on the analysis of the method of slab and floor lifting, this paper will justify the necessity of creating tools to enable choosing the most effective organizational and technical solutions when using this method, and optimizing the processes of using this method for works performance. We suggested to use "complex index for efficiency of applying the method of lifting slabs and floors", represented by a discrete index, which allows to determine the efficiency of organizational and technical solutions in applying the method of lifting slabs and floors. A whole range of factors affecting the formation of a " complex index of efficiency application of the method of lifting slabs and floors" have been studied and proposed. In addition, for mathematical representation of the "complex index of efficiency of application of the method of lifting slabs and floors", we used the method of modeling of multifactor systems, which is presented in this dissertation. The performed studies are preconditions for the formation of a model that will allow us to determine the effectiveness of the organizational and technical solutions in the application of the method of lifting slabs and floors, as well as give appropriate recommendations that will increase the efficiency of production for construction and installation works.


Introduction
Erection of buildings and constructions by the method of slab lifting is one of the promising directions of industrial construction. This method makes possible to combine the advantages of precast and monolithic reinforced concrete. This approach reduces the consumption of basic construction materials and labor costs and opens up wide opportunities for the erection of architecturally expressive buildings and constructions of various functional purposes and storeys.
The concept of constructing multi-storey buildings by lifting finished slabs was first suggested by the French engineer Lafargue, but at the time it could not be realized due to the lack of the necessary lifting equipment. In 1951 the first multi-storey building was constructed in the USA using the slab lifting method. Soon after the experiment with the method of slab lifting became widespread and was used in many countries of Europe and Japan. In Russia, first applied in Leningrad in 1959, it found its further development in the construction practice of Moscow, as well as widely used in cities in Armenia.
The nature of the erection of buildings and structures by the lifting method consists in the fact that at the zero level, large-sized building structures are prefabricated or assembled from individual prefabricated elements, which are then lifted on guiding supports, upwards and without horizontal movement are fixed at the design marks. In most cases, the floor slabs of buildings are produced in sequence one on top of the other in the form of a bundle. The guide supports are reinforced concrete or metal columns as well as reinforced concrete stiffening cores. [2][3][4][5] The stiffening cores are usually made of monolithic cast-in-place or sliding formwork, and reinforced concrete columns are assembled to the height of one or more storeys. The structures are lifted up to the design marks by means of special equipment installed at the bottom of the building or on guide supports. Generally, the frame with the girderless floor slabs of the whole floor is used, as well as with the free grid of the columns. This makes it possible to use floor slabs of any functionally required shape, conditioned by the architectural and planning solution. This is possible because the slab contour is only provided by the edge formwork. As a result, it is possible to design houses with a complicated shape in the plan. Such an architectural and planning solution makes it possible to achieve significant architectural expressiveness of buildings, which is not an end in itself, but should be regarded as a result of solving a set of architectural and urban planning tasks of industrial construction, which creates real conditions for obtaining a significant economic effect [1][2][3][4][5][6]7].
The application of the lifting method in the construction of buildings of various functional purposes allows: -construct buildings of any shape in plan and, if necessary, with different floor heights using a single technology without creating a special construction industry base; -provide solutions to a variety of architectural and urban planning tasks; -carry out the maximum opening of the interior space using large-span frameworks and the free arrangement of columns; -ensure significant payloads can be supported by the large-span frame; -concentrate in one volume of the building premises of different functional purposes; -provide a variety of frame parameters.
The application of the slab lifting method opens up new and expanded opportunities for solving the following industrial construction tasks: -economic use of built-up areas; -rational use of material, technical and labor resources; -optimization of space planning solutions; -improving the comfort of the premises. The application of the methods of lifting slabs and floors has many advantages in relation to other methods of construction of the monolithic reinforced concrete frame of the building. The application of the method of slab lifting allows to widely use for residential buildings the structural scheme with the following configuration of the plans: circle, oval, square, rectangle, rhombus, cross. Around the reinforced concrete core, placing the stair-lift unit and vertical communications, various systems of the ligament frame can be formed. The central location of the stiffening core and the symmetrical solution of the building plan due to the coincidence of the center of mass and the center of rigidity also allows us to meet the regulatory requirements for seismic resistance.
The application of the slab lifting method in combination with the "free" frame makes it possible to form not only point, but also extended structures, including those of different number of storeys. These aspects allow to create compact residential complexes and, as a consequence, to increase the density of urban development. Also, one of the advantages of this method is the possibility to concentrate on a node of vertical communications maximum allowed by the norms of the living area -300 m 2 per floor with one staircase. This is achieved through the use of optimal architectural and planning solutions using the method of slab and floor lifting. At the same time, the comfortable conditions of the apartments, usually associated with the sectional type of house, and hygienic norms are provided. The doublesided orientation of the apartments satisfies the conditions of ventilation, aeration and insolation, which is especially important for the southern regions.
The task of improving comfort in modern housing is solved through the organization of functional areas and their relationship within the space-planning environment of the apartment. Slabs with cantilevered outlets allow for the organization of summer rooms, serving as an important element of the facade composition of the building in a variety of plastic solutions.

Methods
Currently, it is more and more necessary to assess the effectiveness of the adopted organizational and technical solutions in the application of the method of lifting slabs and floors in the construction of buildings and structures. In the scientific literature, quite a number of publications about the recently appeared method of analyzing the organizational and technological component of construction processes, by creating the thesis " the complex indicator of the effectiveness of organizational and technical solutions" are becoming more and more frequent [1,[8][9][10][11][12][13][14][15].
Similarly to today's calculation methodologies, e.g. for concrete compression calculations, where there is an index of ultimate destructive load measured in MPa, it is assumed that the most obvious method of describing the effectiveness of the organizational and technical solutions adopted when applying the method of slab lifting will be a certain numerical, discrete value that is in the relative, assigned range between the maximum (best) and minimum (worst) values [16,17].
Regarding these goals and the research carried out before, it is assumed that the mentioned complex index is a functional correlation with a number of variables characterizing the factors, including both the material and technical conditions and the climatic conditions of the object construction region, which affect the construction and installation works by the floor and floor elevation method. When creating the term "complex index of efficiency of application of the method of floors and ceilings elevation", it is necessary to begin with the consideration of each factor influencing the formation of the final index separately. This is due to the large number of factors affecting the efficiency of construction and installation works by the method of slab and floor lifting [18][19][20][21].
With the purpose of indicating the necessary organizational and technical parameter characterizing the efficiency of the decisions made in the course of works by the slab and floor lifting method, it is recommended to introduce the concept of "complex index of efficiency of the slab and floor lifting method . , which is displayed in the numerical form. We set for the "complex index of efficiency of application of the slab and floor elevation method". The goal of the research is to determine the factors affecting the top of the system in the form of a "composite index of the effectiveness of the slab and floor lifting method. Factors must be endowed with the following properties: to have a significant impact on the final indicator -; be subject to a specific mapping; normalized on a scale -from 0 to +1. Value range: "+1" -best value, "0" -average value, "-1" -worst value [22][23][24][25][26].

Results
After reviewing the scientific literature, we identified the following factors that may have an impact on the effectiveness of methods of lifting floors and ceilings in the construction of buildings and structures: 1. Possibility to combine related construction and installation processes; 2. Level of elaboration of organizational and technological documentation; 3. Climatic conditions during work performance; 4. Qualification level of engineering and technical staff; 5. Level of mechanization of the construction site; 6. The storey and height of the building; 7. Terms of construction and installation works. The next step will be an expert evaluation of the identified factors to determine the most important ones. Factors with the least influence will be rejected, taking into account the 95 percent confidence interval. Then the variation of the selected most significant factors at three levels will be carried out. Finally, the data obtained during the expert survey will be compiled in a mathematical system, through which we can assess the degree of significance of all factors. Significance are recorded in fractions of one ( ).
For the mathematical representation of the "comprehensive performance measure of the slab and floor lifting method," a multifactor systems modeling technique is used. [27] Let us examine the existence of some function y = f (v1), and represent it in the form: where yis the result indicator; (v1, v2, ... , vn) is the union of functionally dependent factors. Now consider a variant where, as a first approximation, the function will have a linear dependence, based on the previously described tree idea, due to the fact that the factors and have a direct relationship. Consequently, expression (1) will take the following form: where is a discrete complex indicator of the effectiveness of the method of lifting floors and floors; (v1, v2 ,….., vn ) -a set of factors; When forming a complex parameter "complex indicator of the effectiveness of the application of the method of lifting slabs and floors" on the basis of the factors (simple parameter) it is necessary to give a description of each individual factor, which we will call "module weight" Wi. In order to obtain this significance we will make an expert evaluation of each individual factor by means of qualimetry. Taking these corrections into account, expression (2) will look like this: where Wiis the weighting factor corresponding to the i-th module. Determination of the weights of each parameter will allow to form an equation of dependence of each required factor on the final "comprehensive indicator of the effectiveness of the method of lifting slabs and floors".

Conclusions
The "comprehensive performance indicator of the slab and floor elevation method" considered in this paper is now in its initial stages of development. However, this work has already given a start to the creation of a model that will allow us to determine the effectiveness of the adopted organizational and technical solutions in the application of the method of lifting slabs and floors. Moreover, to develop and propose appropriate recommendations that will increase the efficiency of construction and installation works, and in particular: reducing the cost, reducing the timing of works and labor costs.