RATIONAL ALTITUDE STRUCTURE FOR PLACING THE WIND EQUIPMENT IN THE CONDITIONS OF UKRAINE

Purpose. For wind observations special wind equipment is used, which should be placed at a certain height above the ground for a relatively short period of time. Such equipment can be transferred from one region to ano-ther. Therefore, the main purpose of the studies outlined in the publication is the selection and justification of the construction of a mobile altitude structure for the placement of wind equipment in the natural and climatic conditions of Ukraine. Methodology . To achieve this purpose, first we chose the type of altitude structure from the existing ones. Next, we determined the nature of the effect of natural and climatic loads on these structures in accordance with the norms of Ukraine. After this, we performed a numerical analysis of the work of altitude structures by the finite element method on the basis of the Lira software. Also, an economic evaluation of the expediency of using altitude structures of a certain type was made, taking into account the lease of the land plot for their location. Findings. According to the results of the conducted studies, it should be noted that for the conditions of Ukraine a steel tower is the most rational mobile altitude structure for placing wind equipment for a relatively small interval of time. In comparison with a steel mast of a similar height, the total cost of its installation and operation is lower. The X-cross brace for steel towers from 50 to 60 m in height is more rational than the K-brace. Herewith, its usage de-creases the construction cost almost by half. Taking into account the possibility of transportation, the separation of the steel tower into assembly units of 8-10 m in length is the most effective. Originality. The authors proposed the method for estimating the economic efficiency of choosing a mobile altitude structure depending on the natural and climatic conditions of the terrain. In accordance with this method, the most rational type of altitude structure is determined taking into account its mobility. Practical value. Application of the proposed approaches and the solutions allows reducing the time required for calculations in design practice and also more reasonably approaching the choice of design solutions for altitude structures.


Introduction
Recently, the opinion on climate change that takes place on the planet is constantly expressed and discussed among specialists from various fields [6][7][8]14]. Therefore, in order to confirm or refute it, more and more studies are being carried out to identify and record various climatic indicators in different regions. Ukraine is not an excep-tion, whose territory is located in different natural zones, including seaside, which allows collecting interesting data.
One of the areas of climate research is wind observation, which allows not only to specify the wind load on building structures, but also to collect the relevant statistics. For this purpose, special wind equipment is used, which is placed at a certain height above the ground (from 5 to 60 m) for 1-2 years, which requires the use of altitude structures.
Since the data collection should be carried out both in urban and in suburban areas with an arbitrary relief and arbitrary buildings (or lack thereof), the use of existing altitude structures is practically impossible. Much more effective is the installation of wind equipment on specially designed mobile altitude structures, which could be repeatedly assembled/disassembled and moved to the desired point of the terrain.

Purpose
Therefore, the main purpose of the studies outlined in the publication is the selection and justification of the construction of a mobile altitude structure for the placement of wind equipment in the natural and climatic conditions of Ukraine.
To achieve this purpose, it was necessary first to choose the type of altitude structure, then to determine the nature of load impact on it, and only then to develop a constructive solution, and with the least possible weight.

Methodology
Among the existing altitude structures, steel masts and towers are the most suitable for accommodating wind equipment and meet the mobility conditions. Therefore, they were identified as basic for further research.
The normative documents in force in Ukraine that regulate the issues of determining the loads on building structures, including altitude structures, are the standard specifications [5]. According to these standard specifications, it is necessary to take into account wind, ice and ice-wind loads for different climatic regions.
Since the projected structure can be located in an arbitrary area on the territory of Ukraine, the load values were taken for the area with their highest values. Such an area is the coast of the Azov Sea, where the identified natural and climatic loads reach maximum values.
For conducting variant calculations an extremely popular and proven numerical method of building mechanics -the method of finite elements [9][10][11][12][13] -was used on the basis of the well-known domestic software complex Lira [4].
Four structural variants of an altitude structure were analysed -a mast with a guy inclination angle of 60 and 45, as well as a tower with X-brace and K-brace. The inclination angle of the mast guys was limited for reasons of reducing the area they should occupy around the structures. The tower brace types were chosen to be the best able to handle loads in different directions and have the highest rigidity.
The height of the structure in both cases was 60 m. The section of the mast was adopted as triangular, and that of the tower -as square, as the most common and tested in practice. Structurally, in all cases, the section of structural elements was assumed to be rounded bending welded profiles, which are also quite affordable, efficient and inexpensive in the modern Ukrainian market. The constructed calculation schemes of the mast and tower are shown in Fig. 1 and 2, respectively. They consisted of core finite elements, and the mask guys were modelled using special finite elements. This approach avoids questions of estimating the convergence of results peculiar for finite elements of other types [1][2][3].

Findings
Based on the calculation results, we obtained the efforts in the altitude structure. The bending moments have the greatest influence on stresseddeformed state of the structures. Their distribution in the form of a mosaic for some of the most typical cases is presented in Fig. 3 and 4.
The calculation results allowed drawing up a summary table, which takes into account the altitude structure mass, as well as total costs, including the manufacture and lease of the land occupied for a term of 1 year ( Table 1). The set value was accepted averaged over Ukraine, because it varies for different regions. However, this analysis reveals the overall picture.
Thus, it is clearly seen from the table that the amount of material (steel) required for placing the mast in comparison with the X-brace tower is more than two times lower, and compared with the K-brace tower -about five times lower.
In calculating the cost of renting a land plot for the location of mobile altitude structure, two options were considered: the first -for urban development, the second -for the countryside (outside the city). At the same time, a significant role is played by the fact that the area necessary for the placement of the mast is much larger than the area occupied by the tower.  Also, the placement of the mast with a guy angle of 45 turns out to be more economical in terms of material content, but, provided the location within the city, the total cost of construction and operation of the mast due to significant land lease is higher than that of the X-brace tower. Also, in city conditions, it is not always possible to rent a large plot of land necessary for placing a mast. These factors make it possible to state that according to the performed researches, it is better to refuse to use the masts, but to prefer the towers, wherein with Xbrace.
A separate issue is the transportation of the chosen structure. To do this, it is planned to be divided into separate transport units. Different schemes of division are possible. The Table 2 shows the assembly unit mass (in kg) for certain schemes. Due to the decrease in the section of the structure in the upper part, the last unit has a smaller mass.
With the first variant of the structure division into 20-meter assembly units, the main advantage is the small number of assembly units themselves, which positively affects the structure reliability, reducing the number of joints. The disadvantage of this division is the emergence of difficulties with transportation, especially within the city. This can lead to additional costs or even the impossibility of transporting units of this length.
The second variant of the division into 10-meter assembly units is the most optimal in both size and mass. A moderate amount of assembly units does not significantly affect the structure reliability.
Considering the third variant of the division into 5-meter units, there are questions regarding the large number of joints in the structure, which potentially can lead to a decrease in the structure reliability. The positive aspects of using such a division should include the ease of installation on the construction site, using lifting equipment with small load capacity.

Originality and practical value
The research presented in the publication allows estimating the possibility of using different types of mobile steel altitude structures for the conditions of Ukraine. Since the existing professional literature and normative base in the design of such structures lack information on possible approaches or recommendations for their design with the possibility of location in all climatic regions of Ukraine, the studies conducted allow reducing the time consumption for practical calculations.
Having determined, according to the above mentioned methodology, the total cost of building and operation of an altitude structure for a certain period of time, it is possible to provide substantiated recommendations on the feasibility of using each of the considered variants of altitude structures.

Conclusions
Based on the material outlined in the publication, the following conclusions can be drawn: 1. For the conditions of Ukraine, the most rational altitude structure to place the wind equipment for a relatively short period of time (1-2 years) is a steel tower. In comparison with a mast of similar height, the total cost of its installation and operation is lower.
2. X-brace for steel towers with 50-60 m height is more rational than the K-brace. Herewith its use reduces almost twice the construction cost.
3. For the purpose of transportation, the most effective steel tower division is considered the one into 8-10 m long assembly units. 4. The presented methodology for assessing the economic feasibility of choosing a mobile altitude structure can be applied to other types of mobile structures as well.