This paper presents the results of experimental testing of the bending strength and modulus of elasticity in edgewise bending of unreinforced and reinforced seven-layer LVL (laminated veneer lumber) poplar veneer panels. The aim of the research is to determine the influence of woven carbon fibers on the improvement of the bending properties and modulus of elasticity of LVL bending in the plane of the plate, as well as the influence of adhesives on the bending properties of the composite product, in order to test the potential of using this newly obtained material as a structural element. Bending was performed on small-scale samples. The main research task is the examination of three types of reinforcement, which differ from each other in position, orientation, and number of layers of reinforcement, using two different types of adhesives: epoxy adhesive and Melamine Urea Formaldehyde Resins (MUF). The composite material was produced in four different combinations in relation to the orientation and position of the reinforcement in the layup. The applied reinforcement is defined through three different configurations (EK1, EK2, and EK3) and a fourth control sample (EK4). Each configuration was produced by applying the two previously mentioned types of adhesives. The research findings showed that in the case of samples produced by applying CFRP (carbon fiber reinforced polymer) using epoxy adhesive, it significantly affected the increase in bending strength and flexural modulus of elasticity. The average improvement in bending strength is 32.9%, 33.2%, and 38.7%, i.e., the flexural modulus of elasticity is 54.1%, 50.7%, and 54.7%, respectively, for configurations EK1, EK2, and EK3, compared to control sample EK4. During the testing, the test samples from reinforced panels EK1 and EK2 showed partly plastic behavior up to the fracture point, while the diagram for the test samples from reinforced panels EK3 shows elastic behavior to a considerable extent, with a significantly smaller plastic behavior zone. This research proved the impossibility of using melamine-urea formaldehyde adhesive to form a composite product based on veneer and carbon fabric. The greatest contribution of this work is the experimentally verified and confirmed result of the possibility of applying poplar veneer to design structural elements in LVL using epoxy adhesive.

The subject of this paper is the elements of a timber lamella structure: the lamellae and their joints. The lamella structure is usually in a diamond pattern, so it relies on additional elements to achieve stability. The analysis of the elements precedes the design of a prototype of a timber lamella vault. The characteristic diamond pattern can be kept for the design of rigid or semi-rigid joints. The design of the joints is challenging, so this paper focused on the analysis and systematization of joints designed for timber lamella structures. The existing timber lamella joints were classified and analyzed based on five parameters: eccentricity, load capacity, the number of elements, easiness of assembly, and adaptability to the circular cylindrical surface, to systemize the existing joints and propose a new one. A design for a new joint was proposed based on the presented joints. The systematization and discussion gave a comparison of all joints, their advantages, and limitations. The conclusion was that the geometry of a circular cylinder and the type of elements for the prototype confirmed all the benefits of the historical lamella structures: uniformity of elements, easy assembly, and economical design.

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