MEMBER Wood Products;

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MEMBER Forest Operations; Pulp, Paper and Bioproducts;

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Cross-laminated timber (CLT) is proving to be a promising solution for wood to compete in building sectors where steel and concrete have traditionally predominated. Studies at FPInnovations found that bare CLT floor systems differ from traditional lightweight wood joisted floors with typical mass around 20 kg/m2 and fundamental natural frequency above 15 Hz, and heavy concrete slab floors with a mass above 200 kg/m2 and fundamental natural frequency below 9 Hz. Based on FPInnovations’ test results, bare CLT floors were found to have mass varying from approximately 30 kg/m2 to 150 kg/m2, and a fundamental natural frequency above 9 Hz. Due to these special properties, the existing standard vibration controlled design methods for lightweight and heavy floors may not be applicable for CLT floors. Manufacturers recommend to use the uniformly distribution load (UDL) deflection method for CLT floor control vibrations by limiting the static deflections of the CLT panels under UDL. Using this approach, the success in avoiding excessive vibrations in CLT floors relies mostly on the engineer’s judgement. A new design methodology is needed to determine the vibration controlled spans for CLT floors. SINTEF’s extensive CLT floor vibration field study found that FPInnovations’ new design method using 1 kN static deflection and fundamental natural frequency as design parameters, predicted bare CLT floor vibration performance that matched well with occupants’ expectations. This criterion was originally developed for wood joisted floors. The new design method is a modified version of the original FPInnovations design method for bare CLT floors based on bare CLT floor test data at FPInnovations. The new design method included the new form of the design criterion using calculated 1 kN static deflection and fundamental natural frequency for bare CLT floors as the criterion parameters, in addition to the new equations to calculate the 1 kN static deflection and fundamental natural frequency. A simple form to directly calculate the vibration controlled spans from CLT stiffness and density was derived from the new design method. Verification showed that the proposed design method predicted well the vibration performance of bare CLT floors studied at FPInnovations with the subjective ratings of the floor vibration performance. The impact study showed that the vibration controlled spans of bare CLT floors predicted by this new design method were almost the same as the spans determined by the CLTdesigner software that was developed in Austria. Working examples were given to demonstrate the procedure of using the simple form of the new design method to calculate the vibration controlled spans of CLT floors.


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