|Contractor:||Naef Partner AG, Architects|
|Reportt:||080624, June 24, 2008|
Several residents of a recently developed area had complained about well audible bang-like noises. Such bangs occurred at any time of the day and there were usual multiple bangs in short intervals. Checking of the situation yielded that the shear studs located between the garage deck slab and the slab over the cellar of an adjacent building were quite probable to be the source of theses bang-like sounds.
To investigate into the situation rci dynamics installed eight accelerometers PCB 393A03 and two microphones in the region under discussion. Six of the accelerometers were installed close to the joint between the two slabs where the shear forces are transmitted through the studs. Two of the accelerometers were installed in the living room in the first floor. The two microphones were installed in a room adjacent to the living room. One of these was connected to an Analyser Norsonic N 121. This stored the measured signals locally. To be provide a common time base with the accelerometer signals the untreated signal of the second microphone was acquired with the same Pimento frontend as the acceleration signals. For the acoustic measurements rci dynamics was supported by the EMPA Section Acoustics.
Instrumentation in the garage (above). The shear studs between the tow slabs can be seen.
Instrumentiation in the living room in the first floor (above).
These signals were continuously monitored for about 100 hours. The sampling rate being s = 25 kHz data acquisition was triggered. A triggered time window consisted of 5 s pre- and 25 s past-trigger time. The trigger level was increased from a = 0.05 m/s2 auf a = 0.5 m/s2 after the first day of monitoring.
During the four days of monitoring a total of 42 relevant events was recorded. The events occurred with time lags of hours. No correlation between the resident’s observations and events recorded was possible during day times when nobody was present in the apartment. Most probably as a consequence of the weather conditions, well audible bangs were registered by the inhabitants during the evening of the first day only. However, these correlated perfectly with the events recorded by the frontend.
Closer inspection of the signals recorded yielded that indeed in most cases an event consisted of several bangs within time intervals of seconds. Comparison of the acceleration signals recorded in the living room and those recorded close to shear stud joint yielded that the latter showed a much larger intensity. However, the noise signals generated in parallel with the acceleration signals were well audible in the living room. The shear studs remained as the most probable source of the bang-noise effects.