Building and ground vibrations
In accordance to ISO 4866, DIN 4150-3 and BS 7385-2
The most recognizable standards for structure vibration measurements are ISO 4866, British BS 7385-2, and German DIN 4150-3. All these three standards use Peak Particle Velocity (PPV) method and FFT to define the Dominant Frequency.
The method for PPV and Dominant Frequency is described in German Standard DIN 4150-3. The PPV is a maximum value of the amplitude of the vibration velocity time-domain signal. The method requires to perform FFT analysis for the PPV, in the way that the middle of a FFT window is placed exactly on the PPV. The result of such analysis is the PPV value and its corresponding Dominant Frequency (DF) for each axis (X,Y,Z). Each pair of PPV and its DF are used as point coordinates that are compared with the limit curve.
DIN 4150-3 and VC curves
The standard DIN 4150-3 may be applied for structures which do not need specific design requirements with reference to dynamic load. The standard defines the values which must be met to avoid damage and impact on structures.
Vibrations are divided into short-term vibrations, which do not occur frequently enough to cause fatigue and do not cause resonance in the assessed structures. Long-term vibrations, on the other hand, are all vibration types which cannot be classified as short-term vibrations.
Vibration velocity values used in the impact assessment of short-term vibrations on structures are divided into three categories, depending on the type of the assessed structure [DIN 4150-3]. Each category features a curve illustrating the permissible vibration velocity limit. The analysis of the measured velocity and the prevailing frequency allows one to obtain a clear picture of the impact of vibrations on the tested structure. The first category and the corresponding Line 1 refers to buildings used for commercial purposes, industrial buildings etc. Dwellings and buildings of similar design and/or occupancy fall into the second category. The third category includes structures that, because of their particular sensitivity to vibration, cannot be classified under lines 1 and 2.
In order to meet American standards (IEST) that uses 1/3 octave bands curves (VC Vibration Criterion curves) expressed in RMS vibration velocity, building vibration meters use 1/3 octaves. The 1/3 octave band method compares RMS results in each band to the limit curve. So in fact the whole spectrum is used for comparison unlike in FFT method where the point (PPV, DF) is positioned versus the curve.
Instruments used to perform measurements as in this standard shall meet the requirements specified in DIN 45669-1. Vibration occurring in a structure can be detected directly using an accelerometer, a displacement transducer or a velocity transducer.
The Peak Particle Velocity is the maximum absolute value of the unweighted signal (particle velocity signal) over the duration of the measurement.
Vibration Dose Value
Vibration dose value measured as the integral of the fourth power of the weighted instantaneous vibration acceleration is used for assesment of severity of impulsive and intermittent vibration (BS 6472:1)
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Building vibration meters shall meet requirements of the standard DIN 45669-1. This standard specifies requirements for vibration measuring systems (vibration meters) and specifies verification procedures that are graded in terms of effort and accuracy. These vibration meters can be used in the field of vibration control to measure mechanical vibrations affecting buildings and/or humans in buildings.
Building vibration meter shall measure vibration displacement, vibration velocity (particle velocity) or vibration acceleration (particle acceleration) and record it r over a given period of time. The detection limit shall be no more than 0,05 mm/s for the peak particle velocity.
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Building and ground vibrations