Utilization of Different Wood Materials in Cross-laminated Timber Elements – A Study of Different Configurations

Sammanfattning

Cross-laminated timber (CLT) is an engineered wood product constructed by combining multiple layers of wood lamellae with adhesives. In the serviceability state, structural timber elements, that are light–weight, are more susceptible to complications regarding the vibration level, than heavier structural elements such as concrete. Contemporary standard practice in the building industry, is to use CLT-plates constructed of the wood species spruce. In Europe, and especially in Sweden, the hardwood species birch is quite common. Previous research indicates that incorporating hardwood in CLT-plates has a great potential of improving the vibration performance of the plate. An engineered product of spruce, namely, densified spruce, can also be used to improve the vibrational performance. The aim of this dissertation is to determine if the performance of CLT-plates can be further improved by incorporating birch, densified spruce or varying strength grades of spruce. The implementation of these wood materials is in terms of constructing various configurations of the CLT-plate, with specific lamellae arrangements of said wood materials. At first, a numerical model was created, modelling the layers in a CLT-plate. This model was used to match the mechanical properties of the named wood materials, to an experiment conducted on CLT-plates of the wood materials analysed in this dissertation. In that capacity, the well–known optimization scheme of Newton–Raphson was used to determine appropriate material parameters. Multiple calibration setups were tested and evaluated based on their normalized relative frequency differences (NRFDs) for the first five modes. A case study, following a systematic approach, was conducted implementing birch, densified spruce and varying spruce strength class, in CLT-plates made of spruce strength class C24. A unit load was imposed on one of the plate corners, with a measure point in the opposite corner, used to determine the acceleration response of the plate. For a more nuanced case study, two differently sized CLT-plates were considered. The case study revealed that implementing the considered wood materials in favour able arrangements in a CLT-plate can significantly reduce the vibration level, without requiring much of the original spruce to be replaced. It was also revealed that greater reduction of the vibration level is obtained when combining spruce and the different wood materials, compared to simply replacing the entire CLT-plate with said materials.