## In-situ acoustic behavior of wooden building element

Delphine Bard

Division of Engineering acoustics, Lund University,

Lund, Sweden

Lightweight constructions made of timber material have a number of advantages; they are cost effective and demand relatively short production duration. One of the main drawbacks of lightweight structures is related to sound transmission. The differences in weight, density, stiffness and repartition compared to traditional materials have repercussions on how the sound propagates in the rooms and in the structures themselves. Sound transmission becomes an increasing nuisance. In order to be able to reduce the sound transmission, a better understanding of how the sound propagates through a real wood cross junction is needed. A series of in-situ measurements using a taping machine and arrays of accelerometers have been performed on a wooden frame building in Limnologen, Sweden. The multi-family house has seven storeys and contains 34 apartments. While the ground floor is cast in concrete, all the seven floors are made of wood, what makes this building a perfect object of study for wood building elements. In particular, the connections of the floor structures between two neighboring apartments have been focused on, since they transfer the horizontal forces in the building.

A previous work had already be presented, with the first measurements results. In the original work, we focused solely on the propagation of sound and vibration from one room on the first floor to the adjacent room on the same floor and to the two rooms above. Here, we extend the investigation further by comparing the former results to the transmission taking place between the fourth and fifth floors. As it was expected, we have found strong similarities between both cases due to similar floor plans. However, we could also observe significant particularities between the former and the latter results. It appears for example that along certain paths, the impact sound propagates much better in higher stories than it does in lower ones. All the results are interpreted, and the results compared with each other, in order to try to provide an explanation of the observed differences. For this, the structure of the whole building has been taken into account instead of just the structure of the concerned rooms. For example, it appears that the structure elements are under much more stress for the lower floors, due to the accumulated weight of the floors above, and that this load might impact the response of the building elements to impact vibration propagating horizontally and vertically through the structure elements.