experimental procedures
4.2 Laboratory test structure
Experimental investigations in the laboratory provide control of con-struction details, easy access, low background noise and flexible sche-duling of measurements. These investigations were carried out on a la-boratory test construction in the facilities of the Lala-boratory for Sound Measurement (LaSM) at the Technical University of Applied Sciences Rosenheim in Germany.
4.2.1 Design of the test structure
In apartment buildings, requirements on maximum sound pressure levels due to service equipment in adjacent apartments have to be met. In typical layouts of apartment buildings, bathrooms or similar rooms that contain service equipment, are often diagonally adjacent. Hence diagonal transmission is an important path that was considered in the design.
The test structure is a full scale two-storey mock-up comprising a timber-joist floor and two timber-frame walls that form a T-junction as shown in Figure 4.1. Detailed drawings of the test structure are given in Figures 4.2 and 4.3. The upper wall is accessible from both sides, and therefore this test structure provides the possibility to measure diagonal and vertical and transmission across the wall-floor-wall junction as well as horizontal transmission in the basement.
The framework of the walls and the floor was designed by the Ger-man timber house Ger-manufacturer Regnauer Fertigbau GmbH & Co. KG.
It represents a common construction in terms of stud spacing and cross sections, but the structure has consciously been simplified. This means that only a single layer of sheeting and no insulation material in the cavi-ties was used as shown in Figure 4.4a. Chipboard was chosen for sheeting as this material can be regarded as an isotropic plate due to the random arrangement of the small wood chips. OSB-boards or plasterboards are orthotropic and therefore more complicated to model.
Normally there are multiple layers of plates and absorbent material in typical timber-frame constructions as this is potentially beneficial
be-4.2 Laboratory test structure
5.06m
2.70m 2.59m2.28m (c) (b)
(a)
Figure 4.1: Sketch of the laboratory test structure. In the following the walls and the floor are denoted as: (a) Lower (timber-frame) wall, (b) upper (timber-frame) wall and (c) (timber-joist) floor.
cause the coincidence dip can be reduced [Matsumoto et al. 2006] or the damping of the structure increased [Trochidis 1982; Schoenwald 2008].
However a major purpose of the laboratory study was to gain insight into the vibrational behaviour of a timber-frame wall. Therefore this ba-sic inhomogeneous construction was chosen to investigate typical aspects of framed structures. As there are only a few models that can deal with multi-layered sheeting [e. g. Sharp and Beauchamp 1969], a single layer of chipboard was chosen to simplify the modelling in SEA.
4.2.2 Construction details of the test structure
As indicated in Figure 4.1, the dimensions of the test structure resemble typical building dimensions. The spacing of the timber studs and the floor joists is 625 mm on centres. A circumferential frame with vertical studs is used for the walls, whereas only parallel aligned joists are used for the floor. The floor joists are perpendicular to the T-junction. All connections within the framework are screwed and no glue is used. The
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A
A
V ≈ 53 m3 (a)
Figure 4.2: Floor plan of basement (dimensions in metres). Dark lines indicate the test structure.
cross sections of the solid spruce beams used for the frame elements are 90 mm × 60 mm for the wall studs and 240 mm × 60 mm for the floor joists.
On both sides of the wall, the chipboard plates are screwed to the fra-mework with a separation of 350 mm. For the covering of the timber joist floor, the same plates are used and identical screw spacings of 350 mm are applied. No ceiling is installed underneath the joists. The boards are arranged such that their longer dimension is perpendicular to the studs or joists, respectively. Hence there are additional horizontal juncti-ons across the wall. As the plates are arranged randomly, the vertical junctions are staggered and do not necessarily occur above studs. All chipboard joints are tongue and grooved without any glue (Figure 4.4b).
4.2 Laboratory test structure
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(a) (b)
(c)
Figure 4.3: Section A-A (see Figure 4.2, dimensions in metre). Dark lines indicate the test structure.
By using elastic layers underneath the lower wall and floor joists, the whole test structure is decoupled from the rest of the building. The walls rest on line supports, the free ends of the floor joists rest on point sup-ports. A resonance frequency of approximately 20 Hz has been estimated as the frequency above which the structure will be isolated from any vibration of the ground floor.
Using the corner of the laboratory, formed by a concrete wall, a drywall, and a segment drywall of approximately 1 m length, the two studwork walls in the basement and the timber-joist floor form a room with an enclosed volume of approximately 53 m3. This room can be entered by a double door that is installed in the drywall segment (see Figure 4.2). The two timber-frame walls in the basement are not coupled to each other, or the building at their vertical boundaries. To avoid airborne sound transmission through the gaps, they are sealed with elastic material. At the T-junction, the floor joists, which are perpendicular to the longer
90 mm × 60 mm Timber stud 19 mm Chipboard 19 mm Chipboard
(a) Section (b) Tongue and groove joint Figure 4.4: Construction of the basic timber-frame wall in the laboratory
lightweight test structure.
wall, are rigidly connected to the framework of the long basement wall using wood screws with a length of 320 mm. The small lower wall is not connected to the timber-joist floor at its upper boundary. The gap is also sealed with elastic material.
The upper wall is placed on top of the sheeting of the floor and fixed with screws connecting the framework of the wall and the floor joists.
Although the construction is stable, additional battens are installed at each end of the upper wall for safety reasons. These are also supported on elastic mounts to decouple the test structure from the laboratory buil-ding. Hence the upper wall has free boundary conditions at three edges and the wall-floor-wall junction in this test structure can be regarded as an isolated T-junction.