Vibrations in a high frequency clt floor panel - Measurement, prediction and evaluation

Sammanfattning: There is an increased need for floors that can accommodate different type of sensitive equipment [1]. Further, it is recommended to design these floors as high frequency floors (HFF) to be able to meet the stringent vibration criteria [1]. This work used experimental measurements and numerical simulations to gain a deeper knowledge about the measurement, prediction and evaluation of vibrations in HFF. The experimental measurements consisted of modal measurements and walking measurements, and a finite element (FE) model was used for the numerical simulations. The test specimen was a CLT floor panel with the dimensions 2.45 m x 2.025 m, consisting of three layers with a total thickness of 80 mm. The purpose of the modal measurements was to validate the material parameters and displacement boundary conditions of the FE-model. From these measurements it appeared that it was possible to find a set of material parameter that was suitable. However, the boundary conditions had a large influence on the dynamic properties of the floor system, and this effect was not incorporated in the FE-model due to its complexity. To investigate the response in the floor triggered by a single pedestrian, twelve different persons walked across the floor in two directions, at three pacing rates. This measurement campaign resulted in a total of 72 measurements. The measured response was evaluated with the one-second running root mean square (RMS). This showed that the response varied to a large extent between individuals, and between the path and position of the transducers. Further, the weight of the persons was measured. It was therefore also possible to evaluate the potential effect of the pedestrian´s mass had on the dynamic properties of the floor. Hereby, the correlation could be observed to be negligible between the mass of the pedestrian, natural frequencies and vibration amplitude, respectively. As recommended in ISO 10137:2007 [2] and ISO 2631-1:1997 [3], the measured response for one sample was evaluated with the RMS, running RMS and vibration dose value. Thereby, it was illustrated that there is some ambiguity in the guidelines about how these quantities should be calculated to ensure comparable results. An FE-model was developed to predict the response from a single pedestrian. The load was applied in the time domain for each footstep. It was found that the vibration in the FE-model is governed by the response at resonance. Furthermore, the effect of varying the striding length and the pacing rate was investigated. This showed that the variation in striding length was negligible, while the change in the pacing rate increased the response.