Although vibrations induced in buildings by ground-borne excitation are often noticeable, there is littleevidence that they produce even cosmetic damage(such as small cracks in plaster). This lack of data isone of the reasons why the British StandardsInstitution (BSI) did not provide guidance before 1992and why there is still no International Organization forStandardization (ISO) guidance limits. It also indicatesthat damage solely attributable to vibrations is notcommon. Some European countries have providedquantitative guidance in their codes for some years;however, it is not strictly valid to apply these limits inthe UK because the data on which they are basedrelate to different structural types and settings.

If there is concern that damage may occur (for example,from piling close to a building), it is important tosurvey the property before exposure to the vibrations(or at the earliest opportunity), measure the vibrationlevels induced and finally check if any damage isevident. It is not enough simply to examine a structureafter exposure and assume that any previouslyunnoticed cracking is a result of the vibrations. Withthis type of problem, accurate measurements andrecords are important. This Digest provides someguidance about what parameters should be measuredand where measurements should be made.

Digest 403March 1995

CI/SfB (J6)

Damage to structuresfrom ground-borne vibration

Ground-borne vibrations from civil engineering, blasting or trafficoften cause noticeable vibrations in buildings. Householders areoccasionally worried that vibrations might damage their propertyand this can be a significant cause of distress.

Guidance levels for damage from ground-borne vibration wereintroduced in two British Standards in 1992 and 1993. This Digestgives information on the current UK position concerning damage tobuildings. A guide to evaluation of human exposure to vibration isgiven in BS 6472 but is not considered here.

This Digest replaces Digest 353 which is now withdrawn.

Technical enquiries to:Building Research Advisory ServiceGarston, Watford, WD2 7JRTel: 01923 664664 Fax: 01923 664098

DEFINITIONSl Particle velocity: velocity of particles set into

motion by the propagation of a disturbancethrough the ground and a structure by a source ofvibration.

l Frequency: the frequency of vibration of suchparticles.

l Peak particle velocity (ppv): the maximuminstantaneous particle velocity at a point during agiven time interval.

l Peak component particle velocity: the maximumvalue of any one of the three orthogonalcomponent particle velocities measured during agiven time interval.

Particle velocity in the soil is therefore distinct fromwave velocity; whilst the disturbance due to a sourcepropagates away from the source with a certain wavevelocity, the ground particles oscillate with a variableparticle velocity.

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There were no British Standards giving guidance on potential damage tostructures from ground-borne vibrations until 1992. The first to bepublished was BS 5228: Part 4 in May 1992; this deals with pilingoperations. Then, in November 1993, BS 7385: Part 2 was issued, coveringmost forms of ground-borne vibration. Since these two codes of practicedo not give exactly the same guidance, some explanation is needed.

BS 5228: Part 4Table 1 (opposite) is abstracted from the standard. The first thing tonote is that the values are suggested as providing a conservativethreshold for minor or cosmetic (non-structural) damage. As such, theycan be thought of as representing good practice for the piling industry.Unlike BS 7385, they make use of peak particle velocity (ppv)measurements, thus ensuring that the maximum velocity is used in anyassessment. The code says that special consideration should be given toancient ruins and listed buildings. It uses the term intermittent vibrations,defined as being a sequence of transient vibrations with sufficientintervals between successive events to permit the amplitude to diminishto an insignificant level in interim periods.

BS 7385: Part 2The recommended vibration levels are given in Table 2 and Fig 1. Theselevels were derived following an extensive review of UK data (whichyielded very few cases of vibration-induced damage), and include theresults of experimental investigations carried out in other countries intovibration-induced damage thresholds. Because they are based onexperimental work, which primarily used the peak component particlevelocity, the guidance given is in terms of this measured value. The levelssuggested are judged to give a minimal risk of vibration induced damage see BS 7385: Part 1. However, it is recognised that ppv should also beevaluated, because this is scientifically the correct measurement to use (itdoes not depend upon orientation) and records quoting frequency andppvs should provide a robust UK database for future codes. The guidevalues in Table 2 have been determined for transient vibrations.Although there is less experimental data for continuous vibrations, it isrecognised that they may give rise to magnification due to resonance.Consequently, for continuous vibrations the guide values in Table 2 mayneed to be reduced by up to 50%, especially at the lower frequencieswhere the lower guide values apply. Important buildings which aredifficult to repair may require special consideration on a case-by-casebasis. A building of historical value should not (unless it is structurallyunsound) be assumed to be more sensitive.

As might be expected from the derivation of the standards, BS 5228generally recommends lower levels than does BS 7385. The exception isthat BS 5228 allows a higher velocity for heavy and stiff structures forcommercial and industrial buildings at frequencies above 50 Hz. This isoutside the main frequency range expected for piling.

BRITISH STANDARDS ON GROUND-BORNE VIBRATION AND DAMAGE

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Status Intermittent Continuousmm/s mm/s

Soundly constructed residential propertyand similar property in good repair 10 5

Structures where preliminary surveysreveal existing significant defectsof a structural nature Reduction of the above values by up to 50%

Light and flexible structuresfor commercial and industrial use 20 10

Heavy and stiff structuresfor commercial and industrial use 30 15

At low frequencies (below 10 Hz), large displacements andassociated large strains necessitate lower ppv values (50% lower).

At high frequencies (above 50 Hz), much smaller strains allow theppv limits to be increased (100% higher).

Table 1 Peak particle velocities which provide conservative thresholds for minordamage from piling operationsDerived from BS 5228: Part 4 and applicable to a frequency range 10 50 Hz

Line Type of building Peak component particle velocitysee Fig 1 in frequency range of predominant pulse

4 Hz to 15 Hz 15 Hz and above

1 Reinforced or framed structures 50 mm/s at 4 Hz and aboveIndustrial and heavy commercialbuildings

2 Unreinforced or light framed 15 mm/s at 4 Hz 20 mm/s at 15 Hzstructures increasing to increasing toResidential or light commercial 20 mm/s at 15 Hz 50 mm/s at 40 Hzbuildings and above

Values are at the base of the building.

For line 2, at frequencies below 4 Hz, a maximum displacementof 0.6 mm (zero to peak) should not be exceeded.

Table 2 Transient vibration guide values for cosmetic damage: from BS 7385: Part 2

Fig 1 Transient vibration guide values for cosmetic damage

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HISTORICALThe basic philosophy has been that it is impracticable to measurevibrations in a large number of buildings and that it is desirable to usesome measurement of the ground vibrations as an indicator ofstructural damage. Several different parameters have been suggested toindicate damage but it is now generally accepted that the best singledescriptor is particle velocity. It is also one of the easiest parameters tomeasure and it is convenient to use such a measurement as a limit toacceptable vibrations levels at, say, the boundary of a construction site.

Obviously, taking measurements outside a building can, at best, be onlya crude indicator of damage potential inside the building. The type ofstructure, design details and state of repair are all important factors andmeasurements inside the building are required to provide a reasonablepicture of what is happening.

MAIN SOURCES OF VIBRATIONThe main sources of man-made, ground-borne vibrations are blasting(quarry, mining or construction), traffic, machinery and civilengineering work, particularly piling. These sources have certaindifferences. For example, blasting may produce high levels of vibrationfor a short period of time, whilst traffic may produce low level, almostcontinuous vibration.

DURATION OF VIBRATIONThe duration of the vibration can have a marked effect on structuralresponse. Continuous vibration may produce a significantly higherresponse due to dynamic magnification if the excitation frequency isclose to a resonance frequency of a structural element. This possibilityof dynamic magnification is the reason why different limits aresuggested for continuous and transient vibrations.

WHAT TO MEASURE AND WHERE TO MEASURE ITThe three orthogonal components of particle velocity (usually onevertical and two horizontal) should be measured simultaneously.Ideally, the response time-histories of each component velocity at eachmeasurement position should be recorded. This will allow the ppv (orcomponent ppv) to be calculated, and the predominant frequency ofvibration to be determined.

Vibration measurements should be made at the base of the buildingfacing the source of vibration. One of the directions of measurementshould be parallel to one of the side walls of the building andmeasurements should be made on the side of the building facing thesource of vibration. If this is not possible, measurements should betaken on the ground outside the building, with the transducers arrangedso that one is in line with the vibration source and at the part of thebuilding nearest the source.

If detailed measurements of the building response are required, theyshould be taken at the foundation and at the uppermost storey and atany positions where damage is expected. The vertical component ofparticle velocity may also be measured at the centre of floors ofintermediate storeys. If the building covers a large area, measurementsshould be taken at several points simultaneously.

MEASURING VIBRATION

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INSTRUMENTATION REQUIREDAs particle velocity is used as a damage indicator, it is preferable tomonitor it directly using a velocity transducer. The most common type isthe geophone. Particle motion in three orthogonal directions should bemonitored at each position in the ground, so three single-axistransducers (or one triple-axis transducer) are required.

In the building, the transducers should be fixed to the measurementposition rigidly so that they give a true record of the particle motion. Insoil, the transducer should be fixed to a stiff, steel rod, 10 mm diameteror larger, driven through the loose surface layer so that it does notproject more than a few millimetres above the surface layer. Furtherguidance and alternative fixing methods are given in BS 7385: Part 1.

The transducer must have a sensitivity and frequency range to cover theanticipated range of vibration frequencies and velocities. BS 7385: Part 1suggests ranges of 1 to 1000 Hz and 0.2 to 500 mm/s. These are extreme:ranges of 4 to 250 Hz and 0.2 to 50 mm/s are more likely. If very lowfrequency vibrations are encountered, it may be difficult to obtainvelocity transducers with the required frequency range and it may benecessary to use accelerometers. Of all man-made ground vibration,blasting produces the largest frequency and velocity ranges.

The signals from the transducer should be displayed and recorded.Displaying the signals directly on an oscilloscope will give an indicationof the vibration levels; recording the response on tape or directly on to acomputer will enable the data to be analysed fully. It may be necessaryto use amplifiers; anti-aliasing filters will be needed if the data arerecorded digitally.

Instrumentation must be calibrated. Individual instruments can becalibrated in the laboratory using a known source or the wholemeasurement chain can be calibrated on site. Recommended proceduresfor calibrating transducers (or pick-ups) are given in BS 6955.

OTHER MEASUREMENTSAfter taking measurements of the ground motion and the response ofthe structure to the excitation, the measurements should be repeatedwhen the source is absent; this provides data on the background noiselevel. Measurements of vibration levels in buildings should also be takenwith people walking near the measurement areas and slamming nearbydoors. This will give an indication of the vibration levels which areencountered normally.

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GUIDELINES FOR SENSITIVE EQUIPMENT

REPORTING

REDUCTION OF VIBRATIONS

ISO 8569 gives provisional guidelines for the measurement and evaluation ofshock and vibration affecting sensitive electronic equipment. This includescomputers, telecommunication equipment and laboratory instruments. Datafrom these measurements can be used to establish a data base which can beused to give guidance on vibration levels to constructors, users, suppliers andmanufacturers of sensitive equipment. There is no explicit guidance onacceptable vibration levels for such equipment so recommended vibrationlevels should be obtained from instrument manufacturers.

The data must be recorded and reported correctly. ISO 8569 provides guidelinesfor the measurement and reporting of shock and vibration effects in buildings.Ideally, the report should include the following:

l name, affiliation and professional standing of person taking measurement

l dates of measurement and weather conditions

l information on source of excitation, including any technical details

l type of soil and any measured soil parameters (especially wave velocity)

l distance of source from structure, horizontal and vertical

l description of structure: room sizes, layout and site location

l building construction type and floor plan

l general structural condition, including list of defects

l transducers, operating ranges and calibration factors

l amplifiers, recorders, analysers and calibrating equipment

l calibration procedures and results

l measurement positions and axes

l individual recorded time histories and maximum calculated particle velocities

l predominant frequencies in time histories

l background noise levels and normal vibration levels

l records of any damage, including photographs.

More details are given in BS 7385: Part 2.

There are three components to any vibration system:

l the sourcel the transmission pathl the receiver (the structure).

To reduce vibration levels at a receiver, it is usually cheaper and easier tomodify the energy input or frequency of the source. Changing the transmissionpath is the most difficult option, although excavating a trench between thesource of vibration and the receiver may appear to provide a physical barrier.Because the trench must be at least 0.3 times the wavelength of the groundwave, this is not normally practicable for low frequency vibrations. Changes tothe receiver can be made, either at the design stage if a vibration problem isenvisaged, or by modifying the existing structure.

A structure may be mounted on supports or bearings to attenuate vibrations.Guidance on the selection and use of elastomeric bearings is given in BS 6177.Alternatively, the resonance frequencies of a structure or structural elementmay be altered by structural changes to avoid problems due to resonance at aparticular excitation frequency.

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RECOMMENDATIONSAnyone undertaking work which will create vibration near housing must beaware that the vibration will be a cause of concern to local residents.Reasonable steps must be taken to control the vibration levels and consequentnuisance. Section 61 of the Control of Pollution Act 1974 provides a meanswhereby an application can be made to the local authority to agree the level ofvibration which should be acceptable on a given site. In itself this may notallay the concern of local residents but following the approved proceduresshould help to minimise problems. Also, if the local authority believe the noiseor vibration constitutes a nuisance and bring an action it would be a defenceto prove that the alleged offence was covered by a relevant consent givenunder the Control of pollution Act 1974.

Householders should realise that construction works do create some vibration.Although people often feel them, these vibrations rarely cause damage toproperty. However, if it is anticipated that human annoyance or structuraldamage may occur as a result of civil engineering works, or other sources ofground-borne vibration, the following steps should be considered.

l If the vibration constitutes a nuisance to occupiers of premises andnegotiation of removal or reduction of the nuisance fails, an action may betaken in court for an order to abate the noise or prohibit its occurrenceunder the Environmental Protection Act 1990.

l If damage is suspected, measurements of the vibration levels, in terms ofparticle velocity, should be made and photographs taken of any damage.Photographic evidence should ideally be of a before and after type. Inaddition, measurements of vibration levels should be made when the sourceof vibration is absent so that a comparison of vibration levels due to thesource of vibration can be made with levels due to everyday activities.

l The Environmental Protection Act 1990 provides that an occupier ofproperty aggrieved by noise (including vibration) which constitutes anuisance may apply to the magistrates court for an order to be issued toabate the nuisance or prohibit its occurrence. Common law may alsoprovide a remedy for a person affected by a noise or vibration, particularlythe law of nuisance and, where there is damage, the law of negligence. Ofcourse, any person who complains about noise or vibration should seeklegal advice on the steps that may be taken to secure a remedy.

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FURTHER READINGControl of Pollution Act, 1974, Part III. London, HMSO.

Land Compensation Act, 1973, Chapter 26. London, HMSO.

ISO 8569. Shock and vibration sensitive equipment. Methods of measurementand reporting data of shock and vibration effects in buildings. (Draft).

British Standards InstitutionBS 5228: Noise control on construction and open sites

Part 4: 1992 Code of practice for noise and vibration controlapplicable to piling operations

BS 6177: 1982 Guide to the selection and use of elastomeric bearings forvibration isolation of buildings

BS 6472: 1992 Guide to the evaluation of human exposure to vibration inbuildings (1 Hz to 80 Hz)

BS 6955: Calibration of vibration and shock pick-upsPart 0: 1988 Guide to basic principles

BS 7385: Evaluation and measurement for vibration in buildingsPart 1: 1990 Guide for measurement of vibration and evaluation oftheir effects on buildings (also ISO 4866 1989)Part 2: 1993 Guide to damage levels from ground-borne vibrations

Other BRE Digests343 Simple measuring and monitoring of movement in low-rise buildings

Part 1: cracks

344 Simple measuring and monitoring of movement in low-rise buildingsPart 2: settlement, heave and out of plumb

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