No abstract

The aim of our research work was to study operation features of plywood structures in flat stress state, which takes place in conditions of real operation of sheet structural materials. The method of study the materials in such conditions was developed. It includes determination of optimal form of specimens and equipment, providing tests of structural plywood under various ratio of values and signs of loads, made in mutually perpendicular directions. The research results of plywood operation from larch timber in conditions of biaxial tension and the assessment of its strength criterion under biaxial tension are shown in the research paper. The values of destructive stresses under various ratio of tension stress, directed along the main axes of elastic anisotropy of the tested material, were obtained. The experimental research results testify to possibility of using the test results of plywood specimens in conditions of biaxial tension and show that addition of extra stress almost does not reduce the strength limit of structural plywood.

Vital problem, occurring in the operation process of structures such as timber beams, is the increase of their bearing capacity and span length with keeping their height. One of the possible ways to solve this problem is steel reinforcement of such structures. The aim of the research work is to show possibility of increasing bearing capacity of single-span reinforced timber beams and develop the main points of calculation and design of such structures. The beam is reinforced symmetrically by 2 rods d28 with both sides with Ar=24.63 cm2 (4d28 A300). The reinforcement is placed in compressed and stretched areas. Reinforced timber structures are designed on two groups of limit conditions. Design on the first limit condition (normal and tangential stress) is made using geometric characteristics of rectangular section of reinforced timber beam. Design on the second limit condition is made taking onto account the timber elastic nodule and inertia moment for reinforced timber beam. The main features of joint work of timber and reinforcement, which can increase operation reliability of bearing structures, are shown in the research work.