Development of engineering wood products based on poplar boards and veneers with composite material insertions for use in construction

Abstract

Nowadays there is a wide variety of research in the field of timber engineering, for both experimental and theoretical parts, however, a close interconnection between them is still needed for a full understanding of the structural behaviour, from its origin (standing trees in forests) until the final products, as structural members (e.g.: glulam beams, solid beams, CLT panels). This thesis is a multi-disciplinary one, where the practical part is embedded with the theoretical part, through the analytical and numerical methods in order to check and validate them. The main timber species studied through this work is focused on poplar timber used in the glulam beams. The work carried out in this thesis starts with evaluating the mechanical properties from standing trees, followed by the characterization in logs, boards, lamellas and in the last step, in the final glulam beams. As poplar is considered a timber material with low-medium quality, different solutions for the improvement of the structural behaviour have been considered through this work. These solutions were divided into environmentally friendly or eco-friendly solutions, for the case when hybrid poplar beams in combination with other timber species were used, and conventional solutions employing CFRP materials were embedded into the specimens’ cross-section. An analytical model, based on the Parallel Axis Theorem (Steiner theorem) and the transformed-section method, is developed to determine the corresponding moduli in tension and compression, based on the global modulus obtained through the bending test for mono-species and multi-species beams. In the following, this model is extended to an analytical model, valid in the linear elastic domain, which can estimate the stresses, strains, resultant forces, and corresponding moduli in tension for the combined section and section with CFRP. Through this analytical formulation, a parametric analysis for the combined beam, pine-poplar, is applied to estimate the mechanical properties of the combined glulam beam as a poplar percentage. The digital image correlation (DIC) technique and finite element analysis (FEA) is applied in the evaluation of the mechanical properties of poplar, subject to tension force. Additionally, the CFRP bonded to poplar with different bond lengths is analyzed from two viewports in order to evaluate the longitudinal strain distribution onto CFRP (fabric and laminate) and on a poplar surface adjacent to the bond line.