Vibration and noise from heavy weapons and explosions

Transcription

1 Vibration and noise from heavy weapons and explosions European Conference of the Defence and the Environment Timo Markula / Akukon Ltd Tapio Lahti / TL Acoustics 22nd May 2013 Helsinki

2 Background FDF has received complaints regarding building damage and annoyance Vibration assessment has been under development in Finland Initial shooting vibration research project Measurements Literature survey 2009-present Measurements Measurement and assessment guide (draft) Large-scale project at an artillery shooting field

3 Building vibration Impulsive and lowfrequency sound waves propagate over long distances, several kms The building vibration is induced by the passing sound wave Figure shows the motion (strongly exaggerated) a) b) c) d)

4 Coupling to structures Building vibration is induced by airborne sound pressure = pressure wave = noise and is coupled to building structures directly from air Building vibration is not a result of groundborne vibration. (opposite to underground explosions)

5 Building response Vibration measured at several one-family houses The houses are sensitive (right) to heavy weapon sound pressure (left) which has maximum at low frequencies 110 sound exposure level L pze, db 0 velocity response ratio, db Hz Hz

6 Damage risk vs. annoyance Vibration is highest at large and structurally mobile surfaces: outer walls, roof, middle floors, windows Annoyance (vibration and rattle) is caused by the vibration of these structures Damage risk is measured from foundations and bearing structures Hence, shooting vibration can be also assessed using measured noise levels outside

7 Guideline values: damage risk The proposed guideline values for assessment of the risk of building damage: Noise outdoors peak sound pressure level L Zpeak 140 db Vibration foundations/supporting structures peak vibration velocity v peak 5 mm/s

8 Guideline values: annoyance The FDF noise guideline values and the proposed vibration annoyance guideline value: Noise, single event C-weighted sound exposure level L CE 100 db Noise, average active day A-weighted equivalent sound level L Aeq,r 55 db (includes +10 db impulse correction) Vibration, single event W m -weighted vibration velocity v W 0.3 mm/s

9 Vibration measurement methods Survey method only noise is measured and the noise level guideline values are used for assessing both vibration and noise Engineering method primary method where noise and vibration at a single position are measured, either from the foundations (damage) or from the walls and floors (annoyance). Advanced method multichannel measurement with noise and multiple vibration measurement positions. Used when the situation is tensed or vibration can be assumed to be close to the limit values.

10 Valokuvia mittauksista ja taloista!

11 vibration velocity level LvWE, db vibration velocity level LvWE, db Measurement results In the measured houses damage criteria (vibration velocity v peak 5 mm/s and peak sound level L peak 140 db) did not exceed. The annoyance criterion v w 0,3 mm/s exceeded in some of the houses with light-weight floors and long spans. Also highest noise levels exceeded annoyance criterion L CE 100 db in some of the houses middle floor vertical 80 foundations horizontal foundations vertical 90 annoyance guideline damage safe limit P1 average P1 max P2 average P2 max P3 average P3 max Fig. 5. An example of vibration measurement results at one site in three different houses (P1 P3) having concrete or stone foundations and wooden base floors. 60 P1 average P1 max P2 average P2 max P3 average P3 max

12 Noise surveys of shooting fields Measurements Emission Immission Calculation Nordic general prediction method Both L Aeq,r and L CE Noise zones (figure) Number of people and summer cottages

13 Abatement Pilot project covers a whole artillery shooting field the aim is to create vibration zones and to determine damage safe zones Abatement would be most effective in planning (distance, terrain obstacles, weather) but often existing cases. The reduction of noise emission of the weapons themselves, or that of the shooting site in general, is very difficult and practically impossible with heavy weapons. There are either no generally applicable techniques for improving the sound insulation of buildings at low frequencies. The reduction of building vibration by making structural changes is not feasible on a large scale, but such changes might reduce rattle in some cases.

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