Traffic-induced building vibrations in Montréal - National Research ...

Hunaidi and Tremblay 7511989) and a multiplication factor of 2. This results in a satisfactoryacceleration value (rms) of 0.01 m/s 2 , which is twicethe perception threshold of the most sensitive people. The rmsor rmq values should be calculated using a 2 s integration timeover the high amplitude portion of acceleration signals.• Method II: Peak acceleration evaluated with respect to thebase value of 0.007 m/s 2 specified by ISO 2631/2 (ISO 1989)and a multiplication factor of 30 together with multiplicationfactors recommended by ISO 2631/2 for the number and durationof events.In the above two methods, acceleration signals need to befrequency-weighted according to ISO 8041 (ISO 1990b). If,on the other hand, velocity signals are measured and the frequencycontent in the signals is mostly above 8 Hz, frequencyweightingis not needed — humans respond equally tovibrations at frequencies at or above 8 Hz. For velocity signals,the base values to be used in methods I and II are 0.1 mm/s(rms) and 0.14 mm/s, respectively.Potential for building damageIn some cases, owners of residential homes may make claimsabout vibration-induced building damage such as cracks inwalls and ceilings, separations of masonry blocks, or cracks inthe building foundation. Although vibration levels in buildingsinduced by road traffic are rarely high enough to be the directcause of damage, they could contribute to the process of deteriorationfrom other causes. Buildings usually have residualstrains in their components as a result of uneven soil movement,moisture and temperature cycles, poor maintenance, and(or) past renovations and repairs. Therefore small vibrationlevels induced in buildings by road traffic (and similarly byother man-made vibrations such as blasting and pile driving)could trigger damage by “topping up” residual strains. Consequently,it is difficult to establish a vibration level above whichtraffic-induced vibration may cause building damage. It can beargued that such damage might be triggered or caused by activitiesin the home such as jumping on stairs or floors andslamming doors, which can induce vibration levels higher thanthose induced by road traffic. On the other hand, it could beargued that activities in buildings cause local and less severedeformation patterns in buildings compared to those caused bystress waves in the ground induced by traffic. Also, whenbuildings are subjected to vibration for extended periods, as forvibrations caused by road traffic, the possibility of fatiguedamage exists if the induced dynamic stresses are high enough.In addition to damage caused directly by vibration, it should beacknowledged that there is a potential of indirect damagecaused by differential movement due to soil densification. Thelatter is particularly known to happen when loose and watersaturatedcohesionless soils are subjected to vibration.In view of the above remarks, it should not be surprisingthat controversy still continues to surround the issue of vibration-inducedbuilding damage. Nonetheless, several countrieshave adopted standards that provide guidance on the evaluationof the effect of vibration on buildings — no such nationalstandards have yet been adopted in Canada; some provinceshave, however, adopted guide values for vibrations induced byblasting, e.g., Ontario (Ministry of the Environment 1978).Vibration levels measured in this study for transit buseswere evaluated to determine their potential for building damage.The following standards and criterion were used:— German standard DIN 4150 (DIN 1984),— Swiss standard SN 640 312 (ASHE 1978),— British standard BS 7385 (BSI 1993), and— U.S. Bureau of Mines (USBM) criterion (Siskind et al.1980).These standards provide guide values in terms of frequency-dependentpeak particle velocity measured in basementsnear foundation walls or on the ground close tobuildings (the German standard also provides values for uppermoststoreys). The probability of building damage due tovibration below the guide values is very small. The internationalstandard ISO 4866 (ISO 1990a), which also deals withthe measurement of vibrations and evaluation of their effectson buildings, does not yet include such guide values (mostlikely due to the controversy that continues to surround thisissue). Damage to buildings is generally defined in the standardsas formation of cracks, falling away of plaster, the enlargementof cracks already present, and the separation ofpartitions or intermediate walls from load-bearing walls. Forresidential buildings of wooden construction and vibration ata frequency of 10 Hz or higher, the lowest guide value in thestandards is that specified by the Swiss standard at 5 mm/s.In this study, only acceleration time histories were measured.Velocity time histories were obtained by indirectly integratingthe measured acceleration time histories in thefrequency domain. In this process, acceleration time recordswere transformed into the frequency domain using a 1024-point fast Fourier transform (FFT) with 50% overlapping Hanningwindows. Then, FFT components below 2.5 Hz were setto zero to avoid low frequency drifting, and those above 2.5 Hzwere divided by the corresponding frequencies. The modifiedFFT spectrum was then inverse fast Fourier transformed(IFFT) to obtain velocity time records. Acceleration levels below2.5 Hz were extremely small (see the section on narrowbandspectra). Hence, errors introduced by discardingcomponents below 2.5 Hz are insignificant.Peak particle velocities of vibrations in basements nearfoundation walls are listed in Table 10 for measurements madein this study for test buses at 50 km/h. It can be seen that peakparticle velocities are well below 5 mm/s, indicating that thepotential for direct building damage was very small. The possibilityof indirect damage caused by uneven soil densificationwas ruled out for most complaint sites in Montréal, as thedominant soil type is silty clay which is very unlikely to settlewhen subjected to vibration. Finally, fatigue-induced damagewas also ruled out in view of the small vibration levels measuredin this study.ConclusionsCharacteristics of traffic-induced building vibrations inMontréal, including transfer functions between vibrations insideand outside buildings, were determined from detailedmeasurements and analysis at nine complaint sites. A typicaltransit bus and city truck were used. Existing standards wereapplied to evaluate human annoyance from building vibrationand the potential for building damage. Also, controlled testswere performed at a selected site to evaluate the effect of road© 1997 NRC Canada