Application Note
By Samuele Ardizio, NVH Specialist, Dewesoft Italy

Today, an increasing number of sources generate vibrations in buildings causing vibration and discomfort to the occupants. Performed by national and international standards objective measurements can establish how these vibrations affect the comfort of the individuals. 

These standards include instructions for the acquisition system as well as mathematical formulas for reference and comparable indexes. The DewesoftX data acquisition software plugin - Human Body Vibration facilitates the experimental procedure to measure according to standards.

Introduction

SIRIUS MINI Data acquisition system with connected accelerometers

Individuals can detect building vibration values that are well below those that can cause any risk of damage to the building – and it may influence their comfort and health.

Vibration accelerations or velocities inside buildings may be measured to assess perceptibility for people inside. Research and studies have been made to evaluate the effect of overexposure to human vibration, especially in the working environment. The results have been used to establish both international and national standards that allow human exposure to vibration to be evaluated. These include particular parameters for assessing the influence on humans, the range of considered frequencies, duration of vibration, and signal processing.

Most of these national standards are based on the International ISO 2631 - Mechanical vibration and shock — Evaluation of human exposure to whole-body vibration. 

In general terms, this ISO presents a detailed series of equipment, procedures, and calculations to experimentally evaluate whole-body vibrations in relation to human health, perception of wellness, or function efficiency. 

Some examples of these standards are the US ANSI-S2.71, the British BS 6472-1, the German DIN 4150, and the Italian UNI9614:2017. The Italian standard UNI9614:2017 is applicable to all buildings that are affected by vibration induced by road or train traffic, heavy machinery, explosions, construction activity, etc. It is not applicable to earthquakes and it is not aimed to evaluate any damage to buildings.

Measurement instrumentation

Measurements conforming with the UNI9614:2017 standard requires:

  • A data acquisition chain compliant to the ISO8041,
  • the weighting curve Wm,
  • a sampling frequency not lower than 1500Hz and suggested ADC resolution 24bit,
  • calibration of the acquisition chain before and after the test, and
  • a sensor sensitivity no lower than 10mV/m/s2.

The Dewesoft catalog offers more data acquisition systems that fulfill these requirements. You can choose among the SIRIUS, KRYPTON, or DEWE-43 DAQ families. 

The right instrument can be selected based on transportability, channel count, AC/DC power supply, and IP protection. During the measurement operation, the Dewesoft solution will also allow you to measure any other kind of physical phenomenon. For example, sound pressure by simply connecting an extra microphone to a free channel of the DAQ system.

Following this approach, it is possible to have, in one shot, both vibration and acoustic characteristics measured at the same time.

Dewesoft data acquisition system DEWE-43A with accelerometers and a microphone.Dewesoft data acquisition system DEWE-43A with accelerometers and a microphone.

For all technical information regarding Dewesoft solutions visit the Dewesoft products webpage.

Software for data storing and post-processing plays a fundamental role in the test scenario for the UNI9614:2017. DewesoftX - Human Body Vibration plug-in enables automation of the complete post-processing analysis but also gives the flexibility to fine-tune all processes thanks to the storing of the raw time signals in parallel to all the on-line mathematics.

Measuring and Post-processing

When measuring vibration in buildings the selection of measurement points is crucial and when applying the criteria for human exposure to vibration, it is important to note that vibration may enter the body along different orthogonal axes. I.e. x-axis (back to chest), y-axis (right side to left side), or z-axis (foot to head).

The UNI9614:2017 standard requires the accelerometers to be positioned at relevant points for the occupants - meaning, for example, in the path of the vibration from the building to the feet of a standing person. 

Measurement spots should be placed in those areas where the occupant is going to spend most of the time like the living room, kitchen, etc..  and areas like corridors, storage rooms, stairs, etc. should be avoided. 

Indication of suited points of measurement in buildings.Indication of suited points of measurement in buildings.

All measurements should be done in 3 axis orientation and the signals should be filtered and weighted with proper weighting curve, Wm. Then, the RMS value sum of the 3 axes should be calculated in order to obtain the total weighted RMS acceleration a(w)(t).

Calculation of the total weighted RMS acceleration a(w)(t). Calculation of the total weighted RMS acceleration a(w)(t).

The time-varying curve a(w)(t) will have a maximum when a disturbing event will occur. 

In DewesoftX - Human Body Vibration software plug-in all this mathematics is already implemented and ready to be selected with a simple click of the mouse. After enabling the plugin simply follow the guidance in the user interface and select the needed indexes.

Measurements are based on an ISO 2631-1 standard that defines basic procedures and ISO 8041, defining the exact procedures for measurements.

Parameters can be calculated either as overall values, having only one value at the end of the measurement, and/or interval logged values with the time interval for logging defined in seconds.

  • RMS - root means square is a statistical measure of the magnitude of a weighted signal.
  • Peak - the maximum deviation of the signal from the zero lines.
  • Crest - the ratio between the peak and RMS. The crest factor gives an impression of the spikes in the signals.
  • VDV - fourth power vibration dose value
  • MSDV - motion sickness dose value.
  • MTVV - maximum transient vibration value, calculated at a one-second interval.

Human body vibration setup screen inside DewesoftX data acquisition softwareThe setup screen in the Human vibration plugin in Dewesoft X

It is also possible to connect more than one triaxial accelerometer transducer to the data acquisition system in order to measure at many different points of the building simultaneously. In this way drastically reduce measurement time and the costs related. 

During the test session, it is possible on-line to calculate all mathematics and check the integrity and quality of the signals.

In addition to that, it is possible to define triggered math calculations. You can select the most critical parts of the signals and directly extract the final index a(w),95 which takes into account the average of the events and their statistical variation.

Thanks to the storing of raw data in parallel to all calculations, you can change all the mathematics and fine-tune the process also in post-processing - days after the actual test. This gives the flexibility also to add deeper analysis for troubleshooting and better diagnosis of the vibration behavior of the building.

All calculated data can be displayed in different formats and prepared for the final report.

Dewesoft X software - display of the final index

Dewesoft X software - display of the final index

Conclusion

Dewesoft data acquisition systems with DewesoftX - Human Body Vibration plug-in is the perfect tool to fulfill tests based on ISO2631 such as the perception of vibration and occupant comfort in residential buildings e.g. according to UNI9614:2017. The plug-and-play setup of transducers and the guided user interface simplifies all the acquisition and analysis process.

Pre-defined mathematics and the modularity of the system allows measuring more than one point at the same time reducing the time-on-site and relative costs. 

In parallel to comfort vibration tests, it is even possible to perform other kinds of measurements like structural integrity and acoustic measurements. One unique tool for all your needs!