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Mechanical Engineers Reference Book 12 Part 15

Tham khảo tài liệu 'mechanical engineers reference book 12 part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 100 Figure 15.173 ISO vibration criteria for a person in a vertical position 0.4 0.63 1.0 1.6 2.5 4.0 6.3 10 16 25 One-third octave band centre frequency 40 63 Hz 100 Vibration isolation and limits 15 137 Octave pass band o 15 min 30 min 2.5 1.6 1.0 0.63 0.4 0.25 Amplitude p Figure 15.172 Human sensitivity Reiher-Meister scale vertical vibration 10 - 1 1 n I -r 1 1 11 1 r 1 1 t 1 T - - - - Painful - - - Imperceptible Just perceptible Clearly perceptibl Annoying Unpleasa - - - 1 1 -1 1- 1 1 dJ L_ _1_ 1 1 1 1 _1_ 15 138 Plant engineering 10 1 02 1 03 1 04 Amplitude im Figure 15.174 Building damage criteria. Zone A - no damage zone B - plaster cracking possible zone c - damage to structure zone D - total destruction At relatively low vibration levels cracks can occur in plaster particularly around windows . At higher levels structural members may crack and ultimately fail. These two types of damage may be easily attributed to mechanical vibration. Another type of damage may result from building settlement caused by ground-borne vibrations compacting the ground differentially beneath buildings. This type of damage is indistinguishable from settlement caused by other occurrences. Specifications for maximum permissible vibrations may be found in DIN standards which are given in terms of maximum velocity in mm s-1 which is allowable for different classes of buildings from ruins and historical buildings up to reinforced concrete structures. More accurate criteria may be found in the technical press and HMSO publications. One such type of drawing is shown in Figure 15.174. 15.9 Acoustic noise 15.9.1 Introduction - basic acoustics Sound can be defined as the sensation in the ear caused by pressure variations in the air. For a pressure variation to be known as sound it must occur much more rapidly than barometric pressure variations. The degree of variation is much less than atmospheric pressure. Audible sound has a frequency range of approximately 20 Hz to 20 kHz and the .