2007 Volume 31 Issue 1 Pages 68-75
Most parts of laboratory experiments concerned with rattling of fittings caused by low frequency sound (hereinafter call LFS) used steady pure sound. This paper describes the result of a laboratory experiment about rattling of fittings by fluctuated LFS, which were recorded around highway bridges. In order to analyze the results, the results by the low frequency sound which was generated by highway bridges, were compared with the results by steady pure sounds. Moreover, in the case of an independent run of a heavy-weighted truck, new experiment data were added to the experiment result of burst sound, which was reported at Vol. 26, No. 2 of Journal of INCE-J, in order to consider the influence of the duration time of low frequency sound, and re-arrangement was performed.
The results are as follows.
(1) The minimum sound pressure level of rattling (hereinafter call MSR) by fluctuated LFS of highway bridges was measured by 1/3 Octave-band and is compared with MSR by steady pure sound. On an average, MSR by fluctuated LFS is larger by 1.5dB than by steady pure LFS.
(2) If the duration time of tone-burst sounds becomes longer, the level difference between MSR of tone-burst sounds and MSR of steady pure sound becomes smaller. When the duration time of tone-burst sounds is longer than 1.0sec, MSR by tone-burst sound is larger by 1dB than by steady pure LFS.
Usually the duration time of LFS generated by highway bridges is more than 1.0sec. From this point, it is suggested that the correction value is estimated about +1∼+2dB for the evaluation of rattling according to LFS generated from a highway bridge.
