Tonkacheiev V. The effective domes of steel bent-welded closed profiles with joints of increased stiffness.

Tonkacheiev V. G. The effective domes of steel bent-welded closed profiles with joints of increased stiffness. - Manuscript. Dissertation for the degree of candidate of technical sciences (doctor of philosophy) in specialty 05.23.01 "building constructions, buildings and structures" (19 - Architecture and construction).- Kyiv National University of Construction and Architecture. - Kyiv, 2018. The aim of the dissertation is to increase the efficiency of constructive solutions of the low-pitched ribbed-ring domes from thin-walled bent-welded rods of the closed profile by substantiating the rational form and finding the optimal parameters of the dome on the basis of theoretical and practical studies of the stability loss phenomenon of a frame of the dome's upper tiers with the "snapping through" effect. The analysis of informational sources on the state of the issue of development of domes covering of buildings and structures was made. The scientific and technical level of theoretical and methodical toolkit for the design of ribbed-ring low-pitched domes has been determined. It was proved that the phenomenon of snapping-through of the dome shell in the upper tiers for shallow domes from bent welded pipes of a closed profile has not been paid enough attention. The goal and the program of experimental studies were established, design and fabrication of the design of the full-size dome cover model in accordance with the parameters that were obtained when choosing a rational design dome covering system and with the help of calculations. To create a test sample and develop a test procedure, the deformed state of the elements of the upper tier of low-pitched dome coverings was modeled with the negative "snapping through" effect and the behavior of the upper tier system has substantiated. The model of the upper tier of the dome consists of the upper support ring, of the ribs, and of the lower support ring. The considered deformation's schemes of the upper tier of low-pitched steel domes provided ideal conditions for the operation of the elements have provided the opportunity to develop a model of the dome behavior by a complex strain scheme to create a test procedure and fabricate a sample for a full-scale experiment. Experiments with rigid and hinged ridge nodes were carried out. The main control parameter during the test was fixation of the vertical displacement of the model's ridge node. The characteristic of loss of stability was considered to be the transition of the system through a critical concentrated load, at which rapid deformation developed. After processing the data, the displacements of the model's ridge joint with a rigid connection of the rods from the load were obtained. Was confirmed the validity of the experimental studies by conducting theoretical experiments using the finite element method using the SCAD Office software package. Two computational models of the von Mises truss for each load stage were created: a model with a hinged connection of rods in the apex of the truss and a model with an elastic joint of the rods. A comparative analysis of the parameters of the stress-strain state of the models of the dome coating structures obtained theoretically using the parameters that were obtained as a result of experiment, was performed. On the basis of the research, recommendations were developed for the calculation and design of dome coverings, taking into account the stability of the upper tier with a rigid apex joint and with bent-welded elements of closed profile. Correction coefficients for the stiffness of elements are proposed for the analytical method for calculating low-pitched ribbed-ring domes with rods from bent-welded rectangular pipes. Based on the research carried out by the author, theoretical positions have been worked out, technical solutions have been substantiated, the introduction of which will make a significant contribution to the acceleration of scientific and technical progress in construction.