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.
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 presents a study of the joint of wooden beams on a new type of aluminum composite connector. For the numerical experiment, beams with a cross-section of 150x220(h) mm made of solid wood were selected. The beams were connected at the same level in a perpendicular direction to each other. The connecting connectors were made of two types of alloys: 7075 T6 and 6061 T6. The experiment was carried out until the joint was completely destroyed under static load. The elastic operation of the node for different types of connectors under study was maintained until the load of 50… 70 kN, after which there was a sharp increase in the deformations of the beams. Conducting a numerical study of the elements of wooden structures made it possible to predict their behavior most accurately in real operating conditions.
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