# Development of a Vibroacoustic Stochastic Finite Element Prediction Tool for a CLT Floor
## 2 Measurements
### Measurement Procedure  
#### 2.2.1 Measurement Setup  
EMA was performed on the CLT slab to characterize the dynamic properties of the CLT slab. The CLT panel was set free at two opposite long sides and simply supported (SFSF boundary condition) with two steel I-beams at two shorter edges (shown in Figure 1b) in order to simplify the boundary conditions. A predefined mesh was drawn on the CLT surface to determine the excitation positions and the measurement positions. In that way, the CLT was divided into five parts in the long direction and three parts in the short direction, which gives a total number of 16 excitation points (the nodes on the short edges were not excited). The size of mesh was decided based upon the highest frequency of interest, i.e., 200 Hz, to avoid the hammer exciting on the nodes of the eigen-modes.  
A single input multiple output system (SIMO) can provide redundant data to better identify the eigen-frequencies and the local modes of complex structures based on different frequency response function (FRF) matrices [20; 21]. Meanwhile, these different FRFs can be used as references to validate the FE model by comparing different simulated FRFs with different measured FRFs. Concerning  
Figure 1: (**a**) Two CLT panels connected by a thin wooden lath. (**b**) One CLT panel simply supported on two I-steel beams.  
the complexity and the inhomogeneity of CLT, the SIMO system was employed to characterize the dynamic properties of the CLT panel via different FRF matrices at different measurement positions. Five uni-axial accelerometers (Bruel & Kjaer Accelerometer Type 4507 001, Bruel & Kjaer Sound & Vibration Measurement A/S, Naerum, Denmark) were attached on the different nodes (red dots in Figure 2) with the help of Faber-Castell Tack-It Multipurpose Adhesive. An impact roving hammer (Bruel & Kjaer Impact hammer Type 8208 serial No. 51994, Bruel & Kjaer Sound & Vibration Measurement A/S, Naerum, Denmark) was used as excitation.  
Depending on the impulse shape and the force spectrum of the impact hammer shown in Figure 3, the medium hard hammer tip was selected for this measurement to ensure most of the input energy localizing within the frequency range of interest (up to 200 Hz). The roving hammer approach was employed. The accelerometers were kept fixing on the selected positions and the hammer were roved over the predefined mesh grid except for the points on boundaries. The accelerometers and the impact hammer were connected to Bruel & Kjaer multi-channel front-end LAN-XI Type 3050. Then, the acceleration signals and the impact force signals were recorded by using the software Bruel & Kjaer PULSE Labshop. There were three averages for each excitation position. The resolution of the FRF was 0.625 Hz.  
Figure 3: (**a**) Impulse shapes of the hammers showing the shape as a function of the used impact tip. (**b**) Force spectra of the hammers showing the frequency response as a function of used impact tip [22] Copyright © Brüel & Kjaer.  
Figure 2: Mesh on the CLT panel. Five accelerometers (red dots) were placed at points 10, 11, 13, 17, and 24), whereas the hammer was moved around all nodes, except on the short edges.