The dissertation is devoted to the development of principles of a qualitative and quantitative assessment of the possibility of the onset of progressive collapse of metal shells of a special kind.
The first section analyzes the existing structural solutions of metal shells of a special type, methods for their calculation and the existing regulatory framework. The works of authors involved in theoretical and experimental studies of metal shells of a special kind are considered. The analysis of anomalies and collapses occurring during the operation of the investigated structures. The main advantages of constructs, their shortcomings, as well as unresolved issues, in particular the problem of progressive collapse, are identified, in connection with which, the goals and objectives of this dissertation were formulated.
The second section describes a laboratory test (on a full-scale specimen) to determine the bending stiffness (relative to the horizontal axis) of a fragment of an arched profile, followed by verification of geometric characteristics obtained using modern calculation systems. Three types of design models of the structures under consideration were investigated: a model in the form of a flat arch (according to the documentation), a model of a spatial smooth shell (reflecting constructive orthotropy), a model in the form of a spatial ribbed shell (reflecting geometric nonlinearity). The algorithm (recommended by the documentation) for studying the stress-strain state (SSS) of special-type structures is supplemented by a stability analysis while taking into account not only the stability of the flat form of bending but also the bending-torsional form of buckling. According to the results of the SSS analysis, based on spatial shell models, the positive effect of the presence of end and intermediate diaphragms on the SSS and the stability of the shells of a special type is proved, and as a result, a conclusion about their constructive necessity is made. The presence of diaphragms leads to decrease the main compressive and tensile stresses (average) by 50-70%, depending on the length of the shell, as well as to decrease vertical displacements (average) by 63% and an increase in the safety factor.
In the third section, the principles of the formation of finite element models of the structures under study are developed taking into account the actual stiffness of the connection profiles and reflecting virtual imperfections. An energy approach is proposed, and based on it, an algorithm for the qualitative and quantitative assessment of the possibility of progressive collapse is developed. Also, measures have been proposed for constructive modernization of the connection nodes of the structures under the study, to avoid progressive collapse.
The fourth section is devoted to verification (during a full-scale experiment) of design models of shells of a special type, before and after constructive modernization. A comparison of the data of the displacements of the studied structural points from the action of the applied concentrated load, before and after the structural modernization was carried out. A significant decrease in displacements by an average of 71.21% is observed, which clearly indicates an improvement in the stiffness characteristics of the system under study. The difference between the theoretical and experimental values of the displacements was, on average, 10.74%.
The fifth section presents the results of the implementation of scientific research in LLC STROY ENGINEERING DEVELOPMENT, during the design and construction of standard sports and fitness complexes.
