Mykhailovskyi D. Consideration of the actual stress-strain state in the units and elements of glued timber structures

The dissertation is devoted to the solution of the important scientific and technical problem of calculation of modern constructions from glued timber taking into account a difficult stress state, and also calculation of modern high-rise buildings with use of panels from cross-glued timber. In the dissertation modern constructions from glued timber, including, long - span and high - rise are investigated. The subject of research is the stress-strain state of long-span arches and frames made of glued timber, taking into account the construction of foundations and soil base, as well as the stress-strain state in the panels of high-rise buildings made of cross-glued timber. The dissertation work highlights the current state of the problem of taking into account the complex stress state in the units and structures of glued timber, the calculation of modern long - span structures taking into account the soil base, formulated the purpose and objectives of research. The calculated conditions for the strength of timber in a complex stress state are obtained. The possibility of applying the fourth energy theory of strength to structures made of solid and glued timber, which are in a complex stress state, as the main one, is substantiated. Numerically obtained coefficients in the calculated conditions of timber strength, taking into account the anisotropy of physical and mechanical properties and the initial level of normal stresses along the fibers. The stress-strain state in curved, one-sloped and two-sloped beams made of solid and glued timber working on bending has been studied. The presence of dangerous places in which the strength of the material will be exhausted under the combined action of stresses before some of them reach the maximum possible values. The stress-strain state of the support zones of bent, double-sloped, single-sloped and rectilinear beams of constant cross section is investigated. Dangerous places from the standpoint of the complex stress state of the support zones of different types of beams are identified and recommendations for their calculation are given. The stress-strain state of long-span structures made of glued timber (frames and arches) was numerically investigated using the finite element method in the LIRA – CAD software package. The influence of anisotropy of physical and mechanical properties on all components of the plane stress state is established.It is determined that from the position of the strength of bent-glued frames there are normal tensile stresses along the fibers in the area of the bisector angle of the bent-glued frames. In addition, the work of long-span structures made of combined glued timber is analyzed, numerous studies are performed by the finite element method and an analytical method for their calculation is proposed by introducing the given characteristics of cross section and modulus of elasticity. Numerically investigated the large-span structures from the glued laminated timber taking into account the construction of foundations and soil base as a system "base-foundation-super-foundation structures".The importance of taking into account the uneven subsidence of the foundations of bent frames and arches, which in turn leads to a significant change in the stress-strain state of cornice units for frames, support units for arches and can lead to failure of long-span structures in general. The existing methods of calculation of panels from cross-glued timber are analyzed. Numerical studies of the stress-strain state of panels made of cross-glued timber in the software complex LIRA-CAD. According to the results of the conducted researches the technique of calculation of panels from cross-glued timber is improved.The methodology of calculation of high-rise buildings with use of panels from cross-glued timber is developed. Numerous studies by the method of finite elements with three-dimensional and flat finite elements of panels made of cross-glued timber, and confirmed the possibility of calculating the panels by modeling flat finite elements with the specified mechanical characteristics of the material according to the proposed method. The possibility of application in modeling of panel multi-storey buildings from cross-glued timber, flat finite elements with the task for them of the resulted mechanical characteristics of material according to the offered technique is proved.