Parametric optimization problem for single edge fold size in cold-formed structural members subjected to central compression has been considered by the paper. Determination the load-bearing capacity of the cold-formed structural members has been performed using the geometrical properties calculated based on the constructed “effective” (reduced) cross-sections taking into account local buckling effects in the section as well as distortional buckling effects. Single edge fold size in cold-formed C-profile has been considered as design variable. Linear convolution of criteria, namely minimization criterion of design area of stiffener cross-section and maximization criterion effective area of stiffener cross-section which defines it reduced load-bearing capacity due to flexural buckling has been used as optimization criterion. The parametric optimization problem has been solved using the method of objective function gradient projection onto the active constraints surface with simultaneous correction of the constraints violations. In order to realize the formulated optimization problem, software OptCAD intended to solve parametric optimization problems for steel structural systems has been used. Optimization results of the single edge folds for the cold-formed С-profiles manufactured by «Blachy Pruszyński» company, «BF FACTORY» company as well as «STEELCO» company have been presented by the paper. The results of the performed investigation can be used as recommendations for companies-manufacturers of the cold-formed profiles, as well as a guide for creation the national assortment base of the effective cold-formed profiles promoting wider implementation of cold-formed steel structures in building practice.
The scientific novelty of this work lies in the description of the methods of calculating and analyzing the symmetrical stability loss of the von Mises truss in the case of sloped loads with an elastic support at the top of the truss. In this work, we consider a deformed layout of the von Mises truss with an elastic support under a concentrated load at the apex joint about the vertical axis. Numerical studies were carried out using the proposed methods. This work indicates the impact of the sloped load and elastic support on the truss' stability loss. We determined dependencies of critical external-load values on the rod's starting pitch for different situations. For each design situation, we obtained generalized expressions for determining critical force values for the truss' apex joint. We obtained dependencies and analytical expressions for determining the critical load on the dome structure, based on the initial geometrical parameters, taking into account the reaction of the elastic support at the apex joint and the direction of the external loads. Our studies show that increasing the support's stiffness increases the sustainability of the von Mises truss. Additionally, we obtained new results required for improving the stability of trusses under a sloped load with an angle of 10-40°about the vertical axis.
Abstract. In this article, the authors conducted a study of the stress-strain and temperature state of the steel frame of the building.Verification analysis of steel section for fire resistance in the homeland software package is carried out.The obtained results were compared with the results of a similar analysis in a foreign software package.The analysis of the dynamic problem of thermal conductivity of the cross section of the beam is carried out.The basic equations for solving the boundary problem of nonstationary thermal conductivity are given.Also, the algorithm of realization of analysis of temperature deformations on section of a steel beam by finite element method is given.The process of designing analytical model of structural elements and analysis of the stress-strain state when operating temperature is changed is considered.The analysis of kinematic and static characteristics of the calculated model under study is carried out.Based on the obtained analysis results, the temperature fields of the beam at certain time intervals are determined.Due to the uneven distribution of temperature in the cross section of the element, temperature deformations are occured.Also, due to the limitation of deformations by external connections, their appearance is accompanied by the development of temperature stresses.Therefore, the study of the peculiarities of thermal deformations in steel structures has considerable practical importance.Due to the urgency of the problem of determining thermal stresses and strains in structures, it is necessary to clarify and improve existing calculation methods, which can not sufficiently take into account changes in time of physical and mechanical characteristics of steel.Therefore, the authors of the article calculated the coefficients of reduction of the physical properties of the section and performed a static analysis of the structure. The change of the stress-strain state of the floor elements under the influence of fire is shown.The results of the analysis showed the importance of taking into account the influence of temperature on the strength and deformation characteristics in the calculation of structures.The authors of the article developed and presented an algorithm for analysing the strength of steel structures for flexibility, taking into account the thermal conduction analysis and the fire resistance analysis.
The paper considers standard methods for determining the corrosion and mechanical characteristics of pipes and their welded joints, steel shell structures for water supply to consumers. It was found that sharp fluctuations in the values of microhardness in the zone of thermal influence of the welded joint exceed the baseline values in the middle part of the weld and the base metal of the pipe. The obtained results can be used to test the performance of carbon steel steels designed for the construction of water towers of long service life in corrosive environments. Under the action of the temperature gradient on the outer surfaces of the walls of the water tank tensile stresses occur, and on the inner surfaces-compressive, which is a favorable factor that reduces the risk of corrosion. Temperature stresses that occur in the case of temperature inhomogeneity along the contour of the cylindrical tank are unfavorable. Stresses from the weight load are small and do not have a significant effect on the destruction of the steel tank, because they are compressive. The value of technological final stresses was determined experimentally by mechanical strain gauge according to the classical method, as well as with the help of electric strain gauges and ultrasonic method according to the method of E. O. Paton Electric Welding Institute (PWI). It has been experimentally established that the most dangerous final welding stresses in assembly seams, the value of which for the longitudinal stress component is close to or exceeds the yield strength , and for the transverse – close to the yield strength , while on steel plates VSt3 of the same thickness . It is likely that welding during installation in conditions of rigid compression of the metal causes an increased level of final stresses. The magnitude and sign of the final stresses significantly depends on the method of installation. Even during block installation, when the water tower is mounted from several pre-annealed blocks, the connection between the mounting ring seams in some areas of the base metal near these seams during fitting creates significant stresses (up to 17.6 kgf / mm2), in some areas – up to 6 kgf / mm2. When sheet assembly stresses can reach a level close to the yield strength.
Seismic resistance of equipment and piping of nuclear power plant units is determined, particularly, by seismic resistance of their steel support structures. A significant number of these structures are located in the reactor building of nuclear power plants and belong to seismic resistance categories I and II. Therefore, such support structures of nuclear power plant equipment and piping, in general, shall perform their functions under seismic hazards that correspond to the safe shutdown earthquake and design-basis earthquakes, respectively. Steel support structures of serial equipment (piping valves, electric and pneumatic drives of piping and pump valves, expansion tanks, etc.) are often designed “on site” in the limited conditions of their actual location. Therefore, it is necessary to design steel support structures of a number of equipment taking into account the fact that it can be connected, in particular, to existing piping with their actual routing. In connection with the above, the research of operation for such support structures under seismic loads is relevant. The article presents the research results for the spectrum of natural oscillation frequencies of the equipment support structure, and the stress-strain state of the considered structure under seismic loads is determined. At the same time, the parameters during normal operation and maximum design basis accident at the nuclear power plant power unit are considered. The calculated combination of loads, which simultaneously includes two episodic impacts (maximum design basis accident and an earthquake) is considered.
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