Wooden multi-span beams with steel reinforcement were studied experimentally on a stationary stand using an eight-point loading scheme that simulated a load uniformly distributed over the beam span. The studies were carried out on beams with a span of 4.8 m with a cross-sectional area of 40 mm × 80 mm, reinforced in the stretched zones of the cross-section with rods made of hot-rolled steel reinforcement of A400 class. The rational zones for the location of reinforcements in the tensioned and compressed zones of the beams were determined. The rational placements of reinforcement in the support and span zones was based on the numerical simulation of the volumetric stress state calculated using the finite element method. It was experimentally confirmed that the failure of wood composite beams had a plastic nature and occurred only along normal sections. This excluded the possibility of brittle fracture from shear stresses and ensured the operational reliability of structures as a whole. It was shown that the proposed rational reinforcement of wooden beams increased their bearing capacity by 175% and reduced bearing deformability by 85%. The results obtained indicated high efficiency of the application of the developed method of reinforcement in beams of roofs and floors of buildings.

Peculiar features of engineering and numerical calculations of wooden beams reinforced with polymeric composites with the local modification of the wood compression area under an insufficient volume of the initial data have been considered in this article. A technique for determining the physical and mechanical properties of materials and a stress-deformation diagram based on experimental investigation has been described. The enlarged algorithm of engineering calculation on the enumerated geometrical characteristics and numerical calculation by the consecutive loading technique and with correcting of the tangent modulus of elasticity at each step instantiated in PC Lira 10.6 has been presented. Analysis of the stress-strain state of wood-composite beams with local modification of wood has been made. Comparative analysis of engineering and numerical calculations has been performed within the limits of the calculated load. Conclusions on the results of theoretical investigations of the proposed beam construction have been formulated and compared with the existing investigations in the field of reinforcement of beam constructions with polymeric composites.

For the composite structures based on wood, that include reinforced wooden structures, allowance for the influence of wood specific features as a building material allows us to evaluate its structural design as accurately as possible and ensure the required reliability and durability. Creep that causes wood deformations evolving in time can be referred to the specific properties of wood to a greater extent affecting the operation of the reinforced wooden structures. Taking into account the state of the issue to determine the effect of the long-acting loads on the stress-strain state of the reinforced glued wooden structures, the article considers the application of the theory of elastic heredity as the most applicable to assess the deformability of wooden structures in time. The conducted experimental and theoretical investigations and the reinforced glued wooden structures observations during the operational process have shown that their stress-strain state changes significantly under the load over time. Glue compositions used to connect reinforcement with wood ensure their reliable joint operation, however, as the result of the wood creep where wood is the basic material, the redistribution of forces between the reinforcement and wood occurs there on and off. At the same time normal stresses in the reinforcement and the glue joint “reinforcement - wood” increase in the calculated cross sections while they decrease in the wood, which is caused by a change (decrease) in the wood elastic modulus. Allowance for the wood creep in the design of the reinforced wooden structures will allow to determine the stress - strain state of the structure in the design more precisely. Therefore, when developing the reinforced wooden structures design standards, this factor must be taken into account.

The article is devoted to the investigation of the technology of the wood-glued structures manufacture with strengthening the supporting zones by a prepreg on the basis of the fiberglass and the glued oligomer with the addition of the carbon nanotubes (CNTs). The peculiarities of the wooden beams cross-sections have been presented. The main types of fiberglass have been reviewed. The article describes strengthening the supporting zones of wooden and glued-wood beams. The method of nanoparticles application in adhesive compositions to improve their physical mechanical properties has been considered. The technological process of manufacturing the glued-wood structure and its strengthening has been developed.

The article is devoted to the study of the short-term and long-term deformations of the lightweight concrete which has found ever-growing use in various fields of construction. The main direction of the lightweight concrete usage is its application in the load-bearing and enclosing structures of buildings and structures. The lightweight concrete has fundamental differences from heavy weight concrete and this is primarily due to the special characteristics of the porous aggregates in their composition. Concretes with such aggregates as expanded clay, expanded perlite and agloportite with strength from 10 to 60 mPas, whose deformative properties are represented by the stress – strain diagram in fig.1, have been investigated in this work. The dependence of the diagrams completeness on the type of aggregate at various concrete strength indexes is given in Table 1. The ascending branches of the diagram for the whole range of the strength has ended when a deformation has reached 2,2·10³. The concrete stress corresponding to the limiting compressive strain of all types of concrete has been 85% of the maximum value. All the diagrams intersect at one point, the descending branches diverge at a stress level of 0.75 and the deformations have been 2,9…3,7·10³. The data obtained as a result of the investigation can be used to calculate the normal sections of bending and eccentrically compressed elements with allowance made to the properties of the lightweight concrete that significantly expand its promising applicable scope in areas with complex geological conditions and in seismic areas.

The article offered the option of reconstruction of a warehouse of wooden structures using modern derivatising materials. The reconstruction involves the insertion of additional overlap of the modified beams. The article deals not only with the calculation of a new type of beams, but also presents the developed technology of their production, tested on test samples. During the tests it was found that the destruction of the beams reinforced with fiberglass with the inclusion of carbon nanotubes in the composition of the adhesive composition is plastic in nature in contrast to the whole-wood beams. When brought to the limit state of the wood rupture of fiberglass impregnated with modified resin does not occur. The use of a new type of beams symmetrically reinforced in the edge zones of beams will reduce the consumption of wood and increase the height of the operated premises in comparison with conventional glued beams.