Building Vibration

1.0 Sources of Building Vibration

• Mechanical equipment
• Users’ equipment
• Rail transportation corridor nearby
• People walking or dancing
• Wind on the façade or roof

2.0 Relevant Standards and Regulations

• Standards of noise exposure experienced steady development over the years, but standards on vibration exposure are not that obvious due to lack of data for the subject matter
• Excessive vibration levels are usually covered due to risk of building structural safety, aspects covering annoyance are not as complete
• ISO 2631: Considers three vibration spectral limits (comfort, work efficiency & danger) with the highest sensitivity in 4 - 8 Hz interval
• Noise generated by vibrations are usually regulated using the L_{Aeq,1h,max} indicator

3.0 Vibration Control

3.1 Source Reduction

• Minimizing the vibratory energy generated by a source through better design or resilient decoupling from the structure
• The most efficient, but the hardest (almost impossible) way, especially rehabilitation projects
• Causes interruption of equipment operation

3.2 Path Reduction

• Implementing expansion joints along the propagation path
• Tricky, hard to consider all the potential problems (especially propagation underground)
• For vibrations are mainly propagated on surfaces, vibration barrier might be useful, as long as, no nearby hard surfaces (reflect vibration causing short-circuit for the barrier)
• For vibrations across building, control measures between foundations and superstructure is possible with springs or resilient elements (close cooperation between structural, acoustic, safety & fire engineer required)

3.3 Receiver Reduction

• Box-in-box construction
• Rooms protected by concrete slab supported with resilient pads or springs

4.0 Vibration Generated Noise

• Vibrating surface will radiate a sound power level, usually, in the low frequency range
• Noise radiation will appear well before any vibratory sensation
• Sound power level, L_w, radiated by a wall of surface, S, excited by vibrations can be expressed as:

Where:

• σ: the radiation factor of the wall
• L_v: velocity level reference 10^(-6) m/s [dB]
• K: constant
• P: perimeter of the surface
• f_g: coincidence frequency
• E: Young’s modulus [N/m^2]
• d: thickness of the plate [m]
• ρ: the volumetric mass of the material
• µ: transversal compressibility coefficient

The radiation factor, σ:

• Examples of 10 log(σ) values:
  i. 24 cm brick wall: 0 dB
  ii. 7 cm concrete: Range (-15 to -5 ) dB until 500 Hz, then 0 dB above
  iii. 13 mm plasterboard: Range(-15 to -5) dB until 2000 Hz, then 0 to 5 dB above

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References

[1] M. Asselineau, Building Acoustics. Boca Raton, Florida: CRC Press, 2015.

[2] M. J. Crocker, Handbook of Noise and Vibration Control. Hoboken, New Jersey: John Wiley & Sons, Inc., 2007