Introduction. With the development of steel frame construction for multi-story civil buildings, the rational design of column assembly joints, based on knowledge of the actual nature of the column stress-strain state, is becoming particularly relevant. These joints are among the key components determining the load-bearing capacity, stability, and spatial rigidity of the frame. Regulatory documents provide limited recommendations for selecting a joint type depending on the column stress-strain state, which requires additional research and calculation and analytical justification. Materials and Methods. This study presents a parametric study of the stress-strain state of the main types of column assembly joints: joints with a milled end, welded and bolted joints on platens, and flanged connections. The joint performance was studied for the most common types of frame systems used in construction practice. The relative eccentricity of the longitudinal force in the column was chosen as the primary criterion determining the applicability of the joint type. The calculated forces were obtained based on the linear calculation of spatial models of frames in the LIRA-SAPR software package. The analysis of the joint performance was performed using the component finite element method in the IDEA Statica software package. The efficiency of the connections was assessed using the coefficient of utilization of the bearing capacity of joint elements (welds, bolts, plates), as well as steel consumption and erection rate.

Results. The dependence of the coefficient of utilization of assembly joint parts and connections on the relative eccentricity and frame type was established. The areas of rational application of various joint types were determined: for m ≤ 0.1 – a joint with a milled end; for 0.1 < m ≤ 2 – a welded joint on cover plates and a flanged joint; for 2 < m ≤ 5 – a welded and bolted joint on cover plates;

for m > 5 – a bolted joint on cover plates. The inappropriateness of using a gap between column elements in overlay connections and the inefficiency of using physical methods to control column assembly joints at m ≤ 0.1 were revealed.

Conclusions. An algorithm for selecting an appropriate type of column assembly joint was developed, taking into account design, structural, installation, and economic criteria. Implementation of these recommendations allows for optimization of design solutions and a reduction in metal consumption and installation labor intensity.

Introduction. The paper considers the stress-strain state of a steel frame with various seismic protection systems. The main purpose of numerical studies was to compare the ability of seismic loads to be dampened by various seismic protection systems and to determine the coefficient of allowable damage K₁ and excess strength Ω for a frame with eccentric braces. Since there is no such constructive system in SP14.13330.2018 when choosing the coefficient K₁, and there are no requirements for considering overstrength, this study will be a big step towards improving the standards for earthquake-resistant construction in our country.

Materials and methods. The study was performed in the SAP2000 software package, considering the physical and geometric nonlinearity. The work of a two-story steel frame with a span of 6 m and a floor height of 3 m with various seismic protection systems was considered. The earthquake was modeled using the 1940 El-Centro accelerogram. A system with a rigid beam-column assembly, a system with concentric braces, a system with eccentric braces, and seismic insulation in the form of rubber-metal supports (RMS) were considered seismic protection. The coefficients K₁ and Ω were calculated analytically based on results of FE-analysis.

Results. The ability to maximize the reduction of forces from the seismic impact of a frame with eccentric braces has been numerically proven, and the efforts in the elements during plasticization of the link (the beam section between the braces) reduce the forces in the elements by up to 76 % compared to other seismic protection systems. The permissible damage K₁=0.222 has been deduced for a frame with eccentric braces. The coefficients of overstrength Ω for frame elements with this type of seismic protection are also determined. For columns, Ω_col=3.47 for braces, Ω_brace=1.8 and for beams, Ω_beam=2.76.

Conclusions. This study has proved the significant superiority of seismic protection based on a system with eccentric braces compared to other systems that are the simplest to implement. The coefficient of permissible damage K₁ and the coefficient of excess strength Ω for this system were also derived. According to the calculation of the K₁ and Ω coefficients, it follows that due to plastic deformations in the brace, the forces in the structural elements are not proportionally reduced. Therefore, the introduction of only the K₁ coefficient, as dictated by SP 14.13330.2018, for calculating seismic impacts is extremely unacceptable, which can lead to the collapse of the structure.

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.

Introduction. The relevance of the topic under study is justified by the discrepancy of the operation data of a wide range of projects of steel structures of building roofs implemented according to the standard series with the instructions of the addendum to p. 15.4.6 of SК 16.13330.2017 "Steel Structures" (rev. 3) on the restriction of the use of purlins as bonding elements.

Aim. A computational and analytical substantiation of the mechanical process of work of the purlins as part of the roofing structures and the phenomenon of changes in its stress-strain state during loading for the actual conditions of connection with the chords of the trusses.

Materials and methods. Particular attention is paid to single-span purlins and their role as bracing elements of compressed chords of trusses when working in the direction from the plane of the truss. Для численного расчета конструкций прогонов использован метод конечных элементов, реализованный в программном комплексе ЛИРА САПР. Предварительно прогон рассматривался как как изгибаемый стержень (балка) на нагрузки от собственного веса, веса кровли и снега. For numerical analysis of purlin structures was used the finite element method implemented in the LIRA SAPR software package. The purlin was previously considered as a bending rod (beam) for loads from its own weight, the weight of roof and snow.

Results. The work of purlins as spacers dividing the compressed chords of trusses into design compartments is substantiated. It has been established that the fictitious force arising from compression of the upper chords of trusses does not have a decisive effect on the load-bearing capacity of purlins, but has an unloading effect when the work of the purlin is combined with the action of the transverse load.

Conclusions. The influence of the determining factors characterizing the inclusion of the purlin in the collaborative work with the roof structures, such as the blackness of the bolt hole, the tightening of the bolted joint force, the influence of the eccentricity of the support of the purlins to the chords of the truss, has been studied. The conducted study allowed us to draw the following conclusions: a purlin is an off-centre-loaded rod that supports loads from its own weight of structures, snow, wind and fictitious forces; by control parameters it was established that the inclusion of the purlins in the work as a bracing element occurs; the combination of the functions of the supporting structure and the spacer in one element increases the strength of the purlins.

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.