Numerical prediction and experimental validation of impact sound radiation by timber joist floors

Abstract

Timber joist floors are widely applied in residential buildings. The accurate prediction of the sound radiated by timber joist floors is challenging due to the interaction between the impacting mass and the floor, orthotropy of the joist and plate components, the effects of the floor size and boundary conditions, etc. In the present work, state-of-the-art approaches for the prediction of impact forces, structural vibration, and radiated sound power were combined into a prediction method for the sound pressure level in a room due to sound radiation by an impacted timber joist floor. This method was then extensively validated in a case study. The natural frequencies and mode shapes of the decoupled joists and plates were both experimentally determined and computed from finite element models, and a good agreement was found when an orthotropic material model is considered for all components. A considerable variation in material properties between nominally identical parts was also discovered. The accuracy of the floor assembly model was subsequently investigated, also by means of modal testing. It was found that a correct representation of the boundary conditions plays a key role in the accuracy of the predicted floor vibration field. Finally, the radiated sound pressure levels were measured and computed. A satisfactory agreement between measurement and computation was observed. At very low frequencies, the interaction between the floor and room modes can play an important role, and a modal room model is employed instead.

Vibration and impact sound properties of hybrid steel-timber floor structures

“…Here, uncertainty is introduced in the simulation model since the damping value proposed by Eurocode 5 [36] applies to low frequencies related to vibrations. A timber joist floor investigated by Wang et al [38] showed an approximate structural loss factor of 0.02 up to 2500 Hz. Although this work deals with a pure timber instead of a hybrid steeltimber floor, the chosen loss factor of 0.02 is deemed acceptable as a first estimate, as currently, no investigations exist on the impact sound behavior of hybrid steel-timber floors such as the presently studied ones.…”

“…Furthermore, the driving-point impedance of the floor is computed from the local Z L and global impedance Z G as follows [38]: with the maximum walking frequency f w = 1.8 Hz and the considered eigenfrequencies f m 3: Compute peak velocity in each mode m: vm ¼ U e;m U r;m I eff;m = mm with U e,m the value of the mode shape m at the excitation position, U r,m the value of the mode shape m at the receiving position, mm the modal mass of mode m 4: From this, calculate the velocity response in each mode over the period of one footfall T with f as the modal damping ratio:…”

“…taken from the FE model at the DOF j of the impact with M jj and K jj as mass and stiffness matrix entries and a material damping coefficient g = 0.0084 for the upper timber plate, which is derived from vibration measurements of the LVL plates. The local impedance is analytically approximated [38]:…”

On the low frequency impact noise of massive floors – a case study

“…Moreover, the interaction of the impact source and the floor was demonstrated which manifests itself especially in the case of light ceilings or reactive floors [4,5]. Ongoing verification and development of effective prediction models with the focus on footfall noise is underway [6,7]. The work of Roozen et al…”

Simulation procedure to determine impact force excitation generated by an ISO tapping machine on a wooden slab

“…In case of wooden floors, general models describing the interaction between the STM and the floor have previously been presented by Amiryarahmadi et al [8], Brunskog and Hammer [5], Coguenanff et al [9], Rabold et al [10], and Wittstock [11]. In the recent decades, the use of the finite element method (FEM) to compute impact sound insulation of wooden floors has raised interests [12][13][14][15][16]. Thus, an appealing procedure would be to compute the impact force excitation by using a FEM tool.…”