Introduction. Paper is devoted to analytical justification of purlins operation as struts based on the study of mechanical processes and stress-strain state. Paper presents additional factors characterizing the inclusion of purlin in joint work with the pavement structures, such as the blackness of the bolt hole, the tightening force of the bolt connection, the influence of the eccentricity of purlin resting on the top chord of truss. As a result of study it was established that pliability of purlin connection to the top chord of truss is not a reason to prohibit the use of purlin as a strut and does not deteriorate its mechanical properties.

Methods. In order to assess the influence of joint pliability purlins’ displacements of when working as part of pavement structures were analyzed, including the eccentricity of the attachment, in spatial formulation of the problem, taking into account the value of bolt tightening force and the influence of friction forces. For numerical calculation of purlin structures used the finite element method implemented in the LIRA CAD software package. Preliminarily, the purlin was considered as a bending rod (beam) for loads from its own weight, roof weight, wind and snow.

Results. The displacements of the upper chords in direction of horizontal load exceed the backlash (1 – 1.5 mm) and vary in range from 0.324 mm to 3.2 mm. Thus, displacements of truss girdles exceed the margin of pliability of connection and characterize operation of the rough hole, including in operation bolted connection of purlin to truss girdle. Inclusion of purlin in work of panel of the upper (compressed) girdle of truss occurs due to triggering of the backlash and the calculated initial imperfection exceeding its value. The calculation methodology for centrally compressed bars includes imperfections exceeding in value the black hole, thus characterizing the insignificance of the possible initial backlash. The friction force arising from uncontrolled tightening of the bolted connection of the purlin to the truss cannot completely prevent the shear forces, forcing the backlash to actuate and include the purlin in operation with the upper chords of the pavement trusses.

Discussion. The support of the purlin on the top belt with vertical eccentricity has an insignificant effect on the displacement of the pavement structures out of their plane of operation, allowing this parameter not to be taken into account in the design scheme. The loading of the purlin with compression forces has a favorable effect on the load-bearing capacity of the purlin, reducing the span moment. The fastening of purlins, as well as of links, is carried out on bolts with the same accuracy (with the same hole blackness). The blackness of bolted connection hole triggers the operation of purlin in the same way as it triggers the operation of braces and struts.

Girder systems, despite their simplicity, are the most common types of structural systems. The design starts with the layout, as a result of which the layout of the ledgers (main and ordinary), the type of coupling (hinged or rigid) and the main criterion for assigning the pitch of ordinary ledgers are selected. Design justification of the assigned layout structural scheme and selection of the most rational solution allows to reduce costs at the stages of the life cycle of the building such as construction, operation, reconstruction or modernization. The accumulated and analyzed volume of the types of applied operational structural solutions of civil building coverings, multiple data on the nature of the development and realization of damage in structures of this type, allows us to formulate the purpose of the study, which consists in the computational justification of the proposed principles and criteria for the development of rational structural scheme of beam coverings. In order to realize this goal, numerical studies have been carried out, considering the variation of the most significant parameters, the change of which affects the result of the search for rational structural schemes of beam covers. According to the results of systematization of the data of the performed work, the algorithm of creation of rational structural solution of beam coverings of non-type geometry is proposed. The algorithm is tested in finding a rational solution of the roofing of an operating building of non-typical shape with plan dimensions 60.0 × 36.0 m.

Introduction. Paper considers methods for analyzing the impact of wind flow on chimney-type frame-and-sheath 12-sided steel cooling tower (SCT) with irrigation area of 1600 m². The main goal of conducting numerical and experimental studies of wind flow around the SCT is to verify the experimental data obtained in wind tunnel, as well as to select turbulence model that most accurately describes the phenomena obtained during experimental studies. The development of chimney-type frame-and-sheath steel cooling towers faces number of unsolved problems, which significantly complicates the design process. The main obstacle is lack of clearly substantiated values of loads and impacts on such structures in current regulatory documents. Wind action, being inconstant in strength and direction, has a significant impact on the bearing capacity of cooling tower, taking into account its shape. These studies will not only clarify the calculated values of wind pressure, but also develop more effective methods for calculating loads on cooling towers.

Materials and methods. The work is based on use of such approaches of construction aerodynamics as tensometric weight studies, method of drainage of models, methods of wind flow visualization "velocimetry", or shadow method, method of silk threads, allowing to fully evaluate the behavior of the structure in wind flow. Using AutoCAD CFD software was performed numerical analysis with subsequent comparison of data obtained results with experimental studies. During experimental part of study were used models made by means of 3D printing for blowing in construction wind tunnel, taking into account the frame of steel casing of cooling tower to determine the actual diagrams of wind pressure distribution on tower frame-casing cooling tower with hyperbolic shape, taking into account the seasonality of operation, as well as stages of construction, to identify the most unfavorable design situations of the wind influence.

Results. The values of the total wind pressure coefficients Cx, Cy, C_Mz have been determined, confirming the high comparability of the experimental data within the range from 95 % to 100 % with national standards. The values and nature of the distribution of local aerodynamic coefficients Cp differ from those proposed in regulatory documents in terms of peak values at an active pressure of 30 % to 50 %, the length of the region and zones with negative pressures that occur when a vortex comes off. The independence of the aerodynamic coefficient Cp from the Reynolds number R_e within the range from 2,71 × 105 to 3,29 × 105. Theory Reynolds Averaged Navier-Stokes SST k-ω DES analysis has been substantiated, most accurately describing the nature of wind flow around design models.

Conclusions. The data of experimental studies allowed to establish the values of the coefficients of total wind pressure, similarity criteria, as well as the values and nature of the distribution of local aerodynamic coefficients on the design of the cooling tower. Based on the results of numerical and experimental studies is proposed refined method for standardizing the wind effect on frame-and-sheath 12-sided steel cooling tower with irrigation area of 1600 m² taking into account the seasonality of operation and construction stages.