In the section 1, an analysis of the current state of research on reinforced wooden structures is conducted, highlighting the necessity for a detailed study of such structures reinforced with composite tapes. Currently, in Ukraine, there is an almost complete lack of research on the combined performance of composite tapes with wooden structures and their mutual influence, which prevents the development of an engineering calculation methodology. However, such research is actively being conducted worldwide, proving its relevance. Practical recommendations for designing wooden structures with composite tape reinforcement are currently lacking in Ukraine, making their development extremely necessary and leading to increased application of such structures in various types of buildings and constructions.
In the section 2, an analysis of numerous numerical studies on the stress-strain state of glued laminated timber (glulam) and cross-laminated timber (CLT) structures reinforced with composite tapes using the finite element method (FEM) in the LIRA-SAPR software package is conducted. It has been proven that glulam beams reinforced with composite tapes have, on average, 18% less vertical deformation and 27% lower normal stresses compared to similar glulam beams not reinforced with composite tapes. Glulam frames reinforced with composite tapes have, on average, 39% less vertical deformation and 57% lower maximum normal stresses in the tensioned zone of the beams. CLT plates reinforced with composite tapes have, on average, 20% less vertical deformation and 32% lower normal stresses compared to similar CLT plates not reinforced with composite tapes. However, selecting a universal method for numerical modeling of glulam and CLT structures in software packages requires further study.
In the section 3, n the third chapter, experimental studies of a full-size sample of a glulam beam reinforced with composite tapes are described. Based on the analysis of the stress-strain state of the glulam beam reinforced with composite tapes from the experiment, it was found that determining the mechanical properties of wood in bending, by testing samples of wood from the same batch, provides reliable modulus of elasticity values for use in the calculation of real structures. An algorithm for conducting experimental studies of glulam beams reinforced with composite tapes using strain gauge techniques is provided. The sequence for reinforcing glulam beams with Sika CarboDur S512 composite tapes is specified. It was found that reinforcing the experimental sample by bonding composite tapes to the tension zone reduces vertical deformations by up to 13%. At the same time, the failure of the reinforced experimental sample occurred at a value 63% higher than the ultimate design load with kmod = 1 and 80% higher than the ultimate design load of the unreinforced experimental sample, considering the kmod factor calculated according to DBN V.2.6-161:2017. The qualitative nature of the stress state of wood obtained from experimental research in glulam beams and glulam beams reinforced with composite tapes clearly shows that the maximum longitudinal stresses in the reinforced beams decreased by up to 42%, the maximum shear stresses increased by up to 57% in the reinforced beams, and the shear stresses increased in some sections by up to 79%.
In the section 4, an analysis of the numerical modeling of the experimental setup is conducted to determine stresses in the sections, assess vertical deformations, and compare the obtained results with actual experimental tests. It was found that the modeling results of the experimental sample in the LIRA-SAPR software environment, where vertical deformations in samples reinforced with composite tapes decreased by up to 17%, confirm the results of reinforcing the experimental sample by bonding composite tapes to the tension zone, where vertical deformations decrease by up to 13%. The qualitative nature of the stress state of wood obtained from numerical research is confirmed by the experiment. Overall, the longitudinal stresses in the tension zone of the examined sections show good correlation. Some differences in the quantitative values of transverse and shear stresses are explained by the peculiarities of the wood structure and the presence of factors that can significantly influence its stress-strain state and, consequently, its overall strength. Strain gauge measurements are very sensitive to the heterogeneous structure of the wood, whereas in the software environment, the wood is idealized.
