Next Generation CLT - Material optimisation of CLT with regard to structural performance by the introduction of air gaps in the cross-layers

Abstract

The construction industry is currently one of the major contributors to the green house gas emissions and the search for more sustainable building materials has led to an increasing demand for CLT. However, the consumption of raw material for the production of CLT is excessively large in relation to the required structural capacity and the inefficient use of timber, in comparison to the required structural capacity, has led to the demand for material optimisation of CLT. The aim of the thesis is to design a material-optimised CLT panel by introducing air gaps in the cross-layers. By designing and manufacturing a variety of three- and five-layer configurations with different air gap layouts and widths, and conducting strength tests on small scale test specimens, the shear capacity is determined and compared with the material reduction of the specimens. Furthermore, finite element analysis of each configuration is performed in order to predict the behaviour of the specimens and to complement the results from the physical strength tests. From the testing, it was observed that the three-layer configurations mainly failed in the bondlines due to inadequate application of adhesive, whereas the five-layer con figurations displayed an even distribution between failure due to panel shear, rolling shear, and deficient bondlines. Furthermore, a significant reduction in strength was noticed for the specimens with air gaps in comparison to the solid specimens and it was concluded to be a clear correlation between the reduction of material and the reduction in capacity. It was also observed that for the specimens with the same air gap widths, a centred air gap layout provided higher stiffness than a shifted air gap layout in general. However, it was concluded that the reduction of material influences the performance of the panel to a greater extent than the layout of the air gaps and the results were verified by the finite element models.