Building Vibration Monitoring During Construction: PN-B-02170, SWD Scales and Third-Octave Bands

Building vibration monitoring during construction is the continuous measurement of vibrations transmitted through the ground from a construction site to adjacent structures and their assessment according to PN-B-02170:2016-12 (damage to structures, SWD-I and SWD-II scales) and PN-B-02171:2017-06 (impact on people). You measure the maximum values of horizontal vibration velocity or acceleration at the foundation, break the signal down into third-octave bands, and compare it with the damage zone. The alarm is an envelope of permissible values across the bands, and every event has a raw trace and a timestamp.

In brief

• Construction vibrations are generated mainly by piling, sheet pile vibro-driving, dynamic compaction, demolition and heavy equipment traffic. Their character differs, as impulse or continuous vibration, as does their frequency range, so a peak value alone does not tell the full story.
• PN-B-02170:2016-12 assesses the harmfulness of vibration for a building in five zones (I-V) on the SWD-I scale (compact buildings, 1-2 storeys) and SWD-II scale (up to 5 storeys), in third-octave bands. PN-B-02171:2017-06 answers a different question: whether people inside the building will feel the vibration and whether it will be disturbing.
• For structures, you measure the horizontal components at foundation level or ground level, in a rigid structural node on the source side. For people, you measure on the floor slab of the room, in three directions. Velocity and acceleration can be converted, but you decide on the choice before installation.
• The engineer needs three views of the same event: the time history, the FFT spectrum and the distribution in 21 third-octave bands from 1 Hz to 100 Hz. Only the third one maps directly to the SWD scale.
• A dynamic envelope alarm compares each band with its own limit value and reacts to the worst one, not to a single spike. An event without the raw trace, timestamp and construction log entry is useless in a dispute.

You will find the general introduction in the complete guide to structural monitoring (SHM). Here we focus on one topic: construction vibrations, how to measure them, assess them and document them.

Imagine a site manager who is due to start impact piling in two weeks, a dozen metres from a 1930s tenement. He worries about two things: that the first resident complaint will arrive after the second day of work, and that a claim for cracks will come six months after handover, when nobody remembers where the piling rig stood. This post gives him what he needs before the first blow: what to measure, where to fasten the sensor, what the alarm should look like, and what record will stand up to an expert report.

Where construction vibration damage comes from

Vibrations from a construction site travel through the ground as waves and reach the foundations of nearby buildings. There, part of the energy enters the structure. Damage does not occur because a building “shakes”, but because vibrations induce additional, cyclically varying strains in elements designed for static loads. Cracks in plaster, cracks above lintels, loss of tightness at joints, these are typical effects well below the level of structural danger, but clearly visible to the owner of the neighbouring tenement.

The second mechanism is indirect and often worse: vibrations densify loose, cohesionless soils beneath the neighbour’s foundation, the building settles unevenly, and cracks look like settlement damage. Without vibration measurements and a baseline survey, you will not later determine what caused it.

Construction vibration sources differ in character, and that determines what to look for in the signal.

How far vibrations “carry” depends on distance, soil type, foundation depth and the building’s technical condition. PN-B-02170:2016-12 gives indicative distances from which vibrations must be considered when designing new buildings: 20 m from construction sources (piles, sheet piles, vibro hammers) and 60 m from vibratory rollers. This is a design guide, not a diagnostic criterion for existing buildings, but as a first answer to the question “is the tenement 18 m from the pile axis within range” it is enough. Experience from one site does not transfer to another; the assessment requires measurement on the specific structure. The organisational and legal context is described in the post about monitoring neighbouring buildings during construction and claims.

What this means for you: if a masonry building stands within several dozen metres of impact or vibratory works, assume the vibrations will reach it and plan the measurement before someone does it for you.

PN-B-02170:2016-12 and the SWD scales

PN-B-02170 is the Polish standard for assessing the harmfulness of vibrations transmitted through the ground to buildings and equipment inside buildings. It does not deal with people, that is the role of PN-B-02171. It answers the question: can vibrations measured at the foundation damage this building? The current edition, PN-B-02170:2016-12 (with amendment Ap1:2017-10), replaced PN-85/B-02170 from 1985. If a contract, decision or expert opinion cites the standard number without the year, confirm which edition is meant. The scales in the 2016 edition are given in frequency-acceleration and frequency-velocity format, and displacement versions were removed.

Two assessment methods

The standard offers two paths: a full assessment (calculation, with dynamic analysis of the building) and an approximate assessment based on SWD scales, or dynamic influence scales. SWD scales apply to masonry buildings made of small-format elements and prefabricated systems (large block, large panel). In construction monitoring, SWD scales are almost always used, because that is the usual neighbouring stock: tenements, single-family houses, low-rise blocks. For structures outside the scope of the scales, larger, taller or of a different structural type, the alarm threshold has to be based on a full assessment or on another justified criterion.

SWD-I and SWD-II: which buildings they apply to

SWD-I applies to compact buildings with small plan dimensions, not exceeding 15 m, one or two storeys, and a height not exceeding any plan dimension. SWD-II applies to buildings no higher than five storeys, whose height is less than twice the smallest width of the building, and also to low-rise buildings, up to two storeys, that do not meet SWD-I conditions. The standard describes the requirements for structural type, foundation and technical condition in detail. Verify them against the standard text before assigning a building to a scale. The scale selection is an engineering decision, and it should be recorded in the monitoring plan together with the reasoning.

Zones I-V: the assessment logic

SWD scales are charts: the horizontal axis is the centre frequency of the third-octave band, the vertical axis is vibration amplitude, acceleration or velocity, and the chart contains four boundary lines (A-D) that divide five zones. We do not reproduce the charts and limit values here. You read them from the standard. The zone logic, paraphrased:

• Zone I - vibrations negligible for the building. Line A is the lower limit from which dynamic influences are considered at all.
• Zone II - vibrations harmless to the structure, but they may accelerate wear and cause the first cracks in plaster and finishes. Line B is the lower limit of cracking in structural elements.
• Zone III - harmful vibrations: local cracking and fissuring, weakening of the structure. Line C is the lower limit of severe damage.
• Zone IV - highly harmful vibrations: numerous fissures, local destruction, risk to human safety. Line D is the stability limit of the structure.
• Zone V - vibrations causing building failure (collapse of walls, falling slabs); the building must not be occupied.

Procedure: for each third-octave band you determine the maximum value from the event, plot the points on the scale and read the zone of the highest one. The worst band decides, not the average. The standard introduces the WODB index for this, the ratio of the band value to line A. The consequence for alarms is clear: the threshold must operate per band, not on a single number for the whole signal.

What to measure and where, according to the standard

The assessment covers peak values of the horizontal vibration components (x, y), in third-octave bands, measured at foundation level or ground level, in a rigid structural node, at the intersection of load-bearing walls, on the source side of the vibrations. The vertical component matters for people and slabs, but it is not part of the SWD scales. Annex A of the standard sets requirements for the measurement chain: frequency recording from 0.5 Hz to 100 Hz (with ±5% tolerance), velocity range from 10⁻⁴ m/s to 1 m/s, acceleration from 10⁻³ m/s² to 10 m/s², accelerometer sensitivity of at least 1 V/g (10 V/g recommended). Before you sign a measurement contract, compare the sensor datasheet with those requirements.

What this means for you: record three things in the monitoring plan, the scale (SWD-I or SWD-II and why), the quantity (velocity or acceleration), and the sensor location. Do not change them during the works. They decide whether the result can be plotted on the scale at all.

PN-B-02171:2017-06: the impact of vibration on people inside buildings

PN-B-02171 is the standard for assessing the impact of vibrations on people staying in buildings and receiving vibrations passively. It answers a different question than PN-B-02170: not “will the building be damaged”, but “will a person in the flat, office or hospital feel these vibrations and will they be disturbing”. The human perception threshold is many times lower than the structural damage threshold, so resident complaints appear long before the first crack, and they are usually the first source of conflict on a site.

The standard idea is this: vibrations are assessed in bands with centre frequencies from 1 Hz to 80 Hz, at the point where a person receives the vibration, on the floor slab of the room, not at the foundation, in three directions relative to the body axis (along the spine and two perpendicular directions). The quantity is the frequency-weighted RMS value of acceleration or velocity across the whole band, or RMS values in third-octave bands compared with perception threshold curves. The permissible level is the perception threshold multiplied by a coefficient depending on the room use (operating theatre, hospital, dwelling, office, workshop), time of day (day/night) and the vibration character (steady or short-term, with the number of events per day distinguished). Detailed coefficients and curves are in the standard.

A construction monitoring programme usually covers both standards: sensors on foundations under PN-B-02170 and, where there are complaints or sensitive rooms, on slabs under PN-B-02171. What this means for you: if you have one sensor and place it on the foundation, you can answer the expert witness, but not the residents. The reverse also does not work.

What to measure: velocity or acceleration, in which directions, and where to mount

Vibration is described by displacement, velocity or acceleration. For a harmonic signal of frequency f, these quantities are linked by the simple relation a = 2πf · v, where v is the velocity amplitude. As an illustration, assume a velocity of 2 mm/s at 20 Hz. This corresponds to an acceleration of 2π · 20 · 0.002 m/s ≈ 0.25 m/s². At 5 Hz, the same velocity gives only about 0.06 m/s². That is why you must not compare numbers without frequency. The same acceleration at different frequencies means a different velocity, and velocity correlates better with masonry damage.

Velocity or acceleration

Structural damage criteria for buildings traditionally use vibration velocity, or PPV, peak particle velocity. PN-B-02170:2016-12 assesses maximum values of velocity or acceleration, and the scales exist in both forms. Accelerometers (MEMS, piezoelectric) measure acceleration and fit easily into a continuous chain. Velocity is obtained from them by integration after the DC component is filtered out. Velocity sensors (geophones) are a separate class of equipment: they measure velocity directly, but have limitations in the low-frequency range, which matters for SWD scales. The decision depends on the scale you are assessing against and should be recorded in the plan, so there is no dispute after the fact.

Strain gauge sensors (vibrating wire), which are standard in static measurements, are not suitable for vibration. The readout of the wire frequency takes too long to capture an event with a frequency of several tens of hertz, as we discuss in the post about vibrating wire sensors and their limitations. For vibrations you need a dynamic chain: a sensor with a high sampling rate and a recorder that stores the raw waveform.

Directions and mounting location

SWD scales concern horizontal vibration, so the sensor must measure two perpendicular horizontal directions, oriented relative to the building walls, parallel and perpendicular to the wall on the source side. The third, vertical axis is used for diagnostics and for PN-B-02171 assessment. Three-axis sensors are standard.

Two common mistakes: a sensor bolted to plaster, which measures plaster vibration rather than wall vibration, and a sensor placed “somewhere in the basement” without axis orientation relative to the walls. You cannot later assign such a measurement to the directions on the scale. What this means for you: installation takes an hour, but if done badly it invalidates months of recording. The detailed qualification of the point, mounting, axes and cable is described in the guide to vibration sensor installation and measurement errors.

Analysis: time history, FFT spectrum and third-octave bands

A peak value for the whole signal is one number, convenient but insufficient, because the SWD scale depends on frequency. The engineer needs three views of one event.

Time history

The time history is the raw record of the measured quantity as a function of time. It answers these questions: when did the event start, how long did it last, was it a single impulse (pile-driver blow), a series of impulses (piling), or continuous vibration (vibro hammer), what was the peak value and on which axis. Without the time history there is no evidence. The spectrum, third octaves and alarm are processed outputs, and the expert witness will ask for the source data.

FFT spectrum

The FFT spectrum, or fast Fourier transform spectrum, is the amplitude distribution of the signal as a function of frequency. It shows which “tones” make up the recorded waveform. For a vibro hammer you will see a sharp line at the operating frequency. For a pile-driver blow, a broad spectrum with energy at low frequencies. For road traffic, a blurred spectrum without lines. FFT is a diagnostic tool. It tells you what is vibrating and whether something in the building is entering resonance. But it has a resolution that the SWD scale does not need, and that is where third octaves come in.

Third-octave bands: 21 bands and why an engineer needs them

A third octave is a frequency band whose upper limit is 2^(1/3) ≈ 1.26 times higher than the lower limit. Three third octaves make one octave. Third-octave bands have constant relative bandwidth. At 2 Hz the band is narrow, about 0.46 Hz. At 63 Hz it is wide, about 14.6 Hz. The standardized third-octave centre frequencies (ISO 266) from 1 Hz to 100 Hz are: 1; 1.25; 1.6; 2; 2.5; 3.15; 4; 5; 6.3; 8; 10; 12.5; 16; 20; 25; 31.5; 40; 50; 63; 80; 100 Hz, 21 bands in total. SWD scales are given in third-octave bands up to 100 Hz, and the standard requires signal recording from 0.5 Hz to 100 Hz. That is where the “21 third-octave bands” in building vibration systems comes from: it is the number of bands covering the scale range, not an arbitrary choice.

Why does an engineer need energy distribution by band when FFT is available? For three reasons:

1. Because the scale is built that way. Assessment under PN-B-02170 means plotting the maximum values from each third-octave band on the scale chart. Third-octave analysis is directly the input to the standard. FFT would still need to be converted.
2. Because third octaves are more resilient. FFT spreads the energy of an impulse across many lines and depends on the window length. A third-octave band collects energy across the range, gives a more stable number and better reflects how structures respond to vibrations.
3. Because the threshold makes sense per band. A masonry building is not equally sensitive across the entire range. The criterion can be exceeded in one band while the global peak value looks harmless.

Illustrative example, hypothetical. Assume two events with the same peak acceleration on the same sensor. The first is a pile-driver blow: energy concentrated in bands from a few to a few tens of hertz, where a compact building responds most strongly. On the scale chart, the point lands high. The second is a heavy dump truck crossing a bump: the same peak value, but the energy is spread across bands in the tens of hertz, where the scale is more forgiving. The point lands lower. An alarm based on “peak value regardless of frequency” treats both events the same. Third-octave analysis distinguishes them. That is the difference between an alarm that means something and an alarm everyone will mute after a week.

Butterworth filters, in one sentence

A Butterworth filter has a maximally flat passband response. In third-octave analysis, a set of such band-pass filters separates each of the 21 bands from the raw waveform without distorting the amplitude in the band you are assessing, and the RMS and MAX values calculated after filtering are the numbers you compare with the threshold.

Dynamic envelope alarm: threshold per band, not on a single spike

In this sense, the envelope is a curve of permissible values drawn above the third-octave bands, one reference value for each band, RMS or maximum. A dynamic envelope alarm is a threshold that compares the event result in each band with that reference value and judges the event by the worst value-to-reference ratio, not by a single sample of the raw waveform.

Why this is better than a simple peak-value threshold:

• Consistency with the standard. Since SWD assessment is per band and the worst band decides, the threshold should work the same way. The envelope can be drawn directly along the boundary line of the zone you want to exclude, with margin.
• Resistance to artefacts. A single sample may be electrical noise or a knock on the sensor. A band value calculated from the whole event requires actual energy to be present there.
• Two levels. A warning threshold, WARNING, as a fraction of the envelope, gives time to react, for example lower hammer energy or a change of method or delivery route. An alarm threshold, ALARM, meaning the envelope is reached, stops the works until the situation is explained. Hysteresis prevents the state from flickering near the threshold.

Where do the envelope values come from? From the SWD scale appropriate to the building, that is the boundary of the zone you want to exclude, with a margin, from the technical condition expert report, and after a few days of background recording, from event statistics so the warning threshold does not trigger on every delivery. The method for selecting and tuning thresholds is described in the post about warning and alarm thresholds in structural monitoring. You read the boundary value from the standard yourself, from the current edition, for the relevant scale and direction. We do not give it here.

What this looks like on your side: the pile driver strikes, the recorder stores the event, the platform calculates the bands and compares them with the envelope, and you receive an SMS at 10:42 with the sensor name and WARNING state, before the neighbour has time to call. You log in, acknowledge the report, and call the pile-driver operator. That acknowledgement stays in the history with your name and the time.

Documenting events for claims

A neighbour’s claim appears weeks or months after the works. At that point it does not matter whether “you had monitoring”. What matters is whether you can show the specific event, its magnitude, its time and what you were doing then. A record that will stand up in a dispute has several features:

Correlation with the construction log is usually the weak point. Hypothetical example: the platform records an event at 10:42, and the log says “piling, axis 5-8”. Was the rig closest to the tenement then, or farthest away? The site manager knows that on the day of the event, not six months later. Good practice is to add a short, dated note on the source on the same day for every event above the warning threshold.

Why this has legal weight

Article 415 of the Polish Civil Code requires compensation for damage caused by fault, and Article 435(1) goes further: the operator, on its own account, of an enterprise set in motion by natural forces is liable for damage caused by its operation regardless of fault. It is exempt only in the event of force majeure or the exclusive fault of the injured party or a third party. Courts also classify construction enterprises using machinery as such enterprises, for example Supreme Court judgment of 17 March 2022, II CSKP 482/22, on damage to a neighbouring building caused by construction works. In practice, you want to be able to show that vibrations from your site did not reach the zone in which structural damage is possible. Electronic records from measurement systems can serve as evidence in civil proceedings (Articles 308-309 of the Code of Civil Procedure), and they are usually interpreted by an expert witness (Article 278 of the Code of Civil Procedure).

Tort claims generally become time-barred after 3 years from the date when the injured party learned of the damage and the liable party, and no later than 10 years from the event (Article 442¹ of the Civil Code), so keep monitoring data at least within that horizon. Under the Construction Law, the site manager must stop the works if there is a possibility of danger and immediately notify the competent authority (Article 22(4)), and the supervisory authority may suspend works carried out in a way that may threaten human safety or property (Article 50). A documented alarm event is the “finding” that allows you to react before the supervisor does.

The features of a reliable record and what to include in the contract with the monitoring contractor are described in the post about monitoring data as evidence in a dispute. What this means for you: the raw trace from the sensor either exists or it does not, and you decide before the first pile-driver blow whether it will exist.

Minimum plan before impact works start

If piling, vibro-driving or demolition next to existing buildings is only a few weeks away, this order is realistic and sufficient:

1. Baseline survey of the buildings within range: description and dated photos of cracks, ideally with the owner present. After the first blow, there is no longer a “before”.
2. Assign each building to SWD-I or SWD-II, or to a full assessment, and record the reasoning in the monitoring plan.
3. Mount a three-axis sensor at foundation or ground level, in a rigid node on the construction side. Where complaints are expected, add a second sensor on the slab.
4. Two to three days of background recording before the works: street traffic, tram, daily life in the tenement. Without background, every alarm will be “from you”.
5. Envelope from the relevant SWD scale and the expert report, warning threshold below it, list of people receiving SMS and email, procedure: who acknowledges, who calls the operator, when the works stop.
6. Contract with the monitoring contractor: raw traces, data export, storage period at least until limitation expires.

What this means for you: points 1 and 4 cannot be made up after the works start, so begin with them.

What it looks like in Inclify

At Inclify, vibrations are handled as dynamic monitoring, separate from static readings, which recorders usually send every 15 minutes by default, or more often. The dynamic recorder works in trigger mode: when the threshold is exceeded, it stores the event with the raw time trace, and the platform accepts samples regardless of transducer type. In the Inclify equipment offer, the team provides MEMS and piezoelectric accelerometers, selected for the structure. For every event you see the time history, FFT spectrum and distribution in 21 third-octave bands from 1 Hz to 100 Hz. There is also an analysis profile with 4th-order Butterworth filters for each band, which requires sampling above 224 Hz. The dynamic envelope alarm compares RMS and MAX in each third octave with a reference envelope per channel: the WARNING level is a fraction of the envelope, ALARM is its attainment, with hysteresis. You enter the envelope in the platform or import it from a CSV file.

Notifications go by SMS, email and in-app to project users according to their preferences. The recipient acknowledges the report, and that acknowledgement, who and when, stays in the alarm history. Silencing always has an expiry time. Raw frames from devices are kept in the communication log for the configured period, by default 7 days. You export dynamic signals to XLSX, data tables to CSV, and vibration events are viewed on the dashboard alongside tilts from the same building. More about the vibration module is on the page /platform/vibration. You enter the envelope values yourself, from the standard and the expert report. The platform does not have built-in SWD scales.

Sources and further reading

• PN-B-02170:2016-12 - Assessment of the harmfulness of vibrations transmitted through the ground to buildings (with amendment Ap1:2017-10). Polish Committee for Standardization: https://sklep.pkn.pl/pn-b-02170-2016-12p.html
• PN-B-02171:2017-06 - Assessment of the impact of vibrations on people in buildings. Polish Committee for Standardization: https://sklep.pkn.pl/pn-b-02171-2017-06p.html
• Stypuła K., “O zmianach w normie PN-B-02170…”, Przegląd Budowlany 10/2017: https://bibliotekanauki.pl/articles/161808.pdf
• Stypuła K., “Wpływ drgań na budynki i ludzi w budynkach - normy i sporządzanie opinii” (PIIB material): https://map.piib.org.pl/uploads/editor/12Stypula-K-Wplyw-drgan-na-budynki-i-ludzi-w-budynkach-popr-66470ee61bfbc.pdf
• Inżynier Budownictwa, “Badania drgań budynków - wytyczne i spojrzenie na normę PN-B-02170:2016-12”: https://inzynierbudownictwa.pl/badania-drgan-budynkow-kluczowe-wytyczne-i-merytoryczne-spojrzenie-na-norme-pn-b-021702016-12/
• ISO 266:1997 Acoustics - Preferred frequencies (third-octave centre frequencies): https://www.iso.org/standard/1350.html
• Act of 23 April 1964 - Civil Code (Articles 415, 435, 442¹): https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU19640160093
• Act of 17 November 1964 - Code of Civil Procedure (Articles 278, 308, 309): https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU19640430296
• Act of 7 July 1994 - Construction Law (Articles 5, 22, 50): https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU19940890414
• Supreme Court judgment of 17 March 2022, II CSKP 482/22 (liability of a construction enterprise under Article 435 of the Civil Code): http://www.sn.pl/sites/orzecznictwo/orzeczenia3/ii%20cskp%20482-22.pdf

What next

If piling, vibro-driving or demolition is ahead of you next to existing buildings, start with one building: a vibration sensor on the foundation, optionally a second one on the slab, an envelope from the correct SWD scale and an alarm with notifications to the site manager. Do it before the first pile-driver blow. Background and baseline condition can only be measured then. If you already have sensors and recorders, connection to the platform takes a few days. Full deployment, including installation, takes from several to several dozen weeks. Describe the structure, the distance to neighbours and the work method, and we will reply within 24 hours: let's talk about vibration monitoring on your site.