Comparison of Calculation Methods for Vibration Analysis of Concrete-CLT Composite Floors

Abstract

Although the field of vibration has been researched for a long time, the existing guidelines for timber floors are still limited and under development. As a lightweight structure, wood floors are more likely to experience unwanted vibration than heavier floors (such as concrete), but the addition of a concrete layer on top of the timber element increases the effective stiffness of the floor system, which plays a major role in the vibration behaviour of the floor. Therefore, the aim of this work was to investigate the accuracy of different vibration methods for predicting the vibration behaviour of a timber-concrete composite floor. To this end, three relevant guidelines (SFS-EN 1993-1-1 NA+NCCI, prEN1995-1-1:2023 (E) and SCI publication P354) were analysed and compared. The results obtained were also compared with site measurements taken on a CLT-concrete floor, part of a multistorey building. The site measurements referred to the natural frequencies detected on the floor at two locations. Multiple measurements were taken at each location and the values used for the comparison were the average of the fundamental frequencies detected at each location. If a quick estimation of the vibration performance of the floor is required or a pre-dimensioning, this study shows that the method proposed in prEN1995-1-1:2023 (E) is preferable. This approach showed a wider range of applicability and provided more accurate results compared to the site measurements. This analytical method is easy to apply and still gives conservative results. In the study, the fundamental frequencies obtained by this method were about 8 Hz lower than the measured data. The outcomes of this study showed that the SFS-EN 1993-1-1 NA+NCCI method has many limitations in its application and provides very conservative results, such as the calculated fundamental frequency results being about 9 Hz lower than the measured data. It has the advantage of being an analytical method based on simple formulas. Therefore, it is a quick tool to use when applicable. The FEM modal and response analysis proposed in the SCI publication P354 gave the most accurate results and the calculated fundamental frequency was 2-3 Hz lower than the site measurements. This approach is recommended for detailed analysis where sufficient information is known about the floor structure and its joints. This method is more time consuming and requires more skills to properly model and evaluate the floor system. On the other hand, it leads to more accurate and closest results to the real vibration behaviour of the slab.