Stresses and Strains in Glulam Due to Moisture Change - Differences between Testing and Service Conditions with Reference to Various Wood Species

摘要

The aim of these research studies has been to visualize and compare strains during drying of various wood species regarding both conditions of delamination tests and climate conditions in buildings and timber structures. Due to their growth conditions, natural durability or strength, it is assumed that the selected wood species will gain in importance in Central Europe for wood engineered products, such as glued laminated timber. Thereby the bonding technology plays a key role. High resistance to delamination is an approved indicator of a glue line's quality. However, hardwoods often do not meet the challenging requirements of a delamination test. To reveal differences between testing and service conditions with regard to various wood species, optical deformation analyses were carried out with a non-contact measuring system. Visualized strains of test specimens subjected to various climate conditions show the differences of drying characteristics of wood species. Profound knowledge of the moisture induced stresses is needed to evaluate the performance and usability of bonded wooden products in reality. Test series of optical measurements show normal and shear strains with respect to wood species. Ratios of moisture induced strains occurring in structural members relative to strains occurring in delamination test samples were determined. However, not just one single wood species shows maximum or minimum values over all test series and climate conditions. To study the impact of strains on a glue line further, future research work will be carried out by means of finite element method (FEM) based calculations.