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

740Can. J. Civ. Eng. Vol. 24, 1997Fig. 2. Typical acceleration signals induced by (a) emptybusand(b) loaded truck at 50 km/h.using digital filters of the recursive type, which conform tospecifications of band-limiting and band-pass filters for frequencyweightings W xy and W z per ISO 8041 (ISO 1990b) inthe horizontal and vertical directions, respectively (see Al-Hunaidiand Guan (1996) for details). Root-mean-square values of frequency-weightedacceleration signals were then calculated usingthe same integration time and discarding the same numberof initial averages as for the 1/3 octave band analysis describedabove.Narrow-band frequency analysisNarrow-band frequency analysis using the fast Fourier transform(FFT) was performed in order to resolve in detail thefrequency content of the measured vibration signals. Thenumber of points used in FFT calculations was large enough tocontain the major part of the signal. This eliminated the needfor smoothing windows, hence avoiding difficulties associatedwith these windows in the analysis of transient signals (Al-Hunaidiet al. 1994).Transfer functionsTransfer functions (i.e., ratios) between different measurementpoints were calculated for both the 1/3 octave band and frequency-weightedacceleration values. Transfer functions werefirst calculated for acceleration values obtained for each vehiclepass-by. Then a mean value was calculated from threevehicle pass-bys for the same test.It should be noted that unlike transfer functions obtainedfrom usual spectral analysis methods, the method describedabove does not provide a measure for judging whether the vibrationsignals at the two particular points used in the transferfunction calculation are coherent, i.e., generated by the samesource. In this study, coherence between vibration signals wasverified in two ways. First, a comparison was made betweenambient vibration values and those due to test vehicles. In thefrequency range of 8 to 25 Hz it was found that vibrations inducedby test vehicles are much higher than ambient vibrations;elsewhere this was not so. This was taken as an indication ofcoherent signals only for 1/3 octave frequency bands from 8 to25 Hz. Second, in the frequency range for 1/3 octave frequencybands between 8 and 25 Hz, the minimum and maximum oftransfer functions obtained for each band from three test repetitionswere compared. In most cases, there were insignificantdifferences and again this was taken as an indication of coherencebetween the signals in the said frequency range.© 1997 NRC Canada

© 1997 NRC CanadaFig. 3. Vertical acceleration (rms) for 1/3 octave frequency bands and frequency-weighted (FW) acceleration — bus at 50 km/h.Hunaidi and Tremblay 741

742Fig. 4. Vertical acceleration (rms) for 1/3 octave frequency bands and frequency-weighted (FW) acceleration — truck at 50 km/h.Can. J. Civ. Eng. Vol. 24, 1997© 1997 NRC Canada

744Fig. 5. Transfer functions between rms acceleration values at points inside and outside buildings.Can. J. Civ. Eng. Vol. 24, 1997© 1997 NRC Canada

Hunaidi and Tremblay 747Fig. 6. Layout of site 9 showing location of wood plank attached to road surface. (All dimensions are in meters.)value was for the second-storey measurement point; ratioswere higher at other points in the building). For PSR values of4 and 0 representing road conditions before and after resurfacing,Rudder’s (1978) approximate relationship would give areduction factor of 6.9. This is in good agreement withthe minimum reduction factor of 6.4 found above. Therefore,it may be a reasonable suggestion for the time being to applyRudder’s relationship for site conditions in Montréal. Needlessto say, however, more tests at other sites having PSR valuesdifferent from that of the site selected in this study would berequired to further validate the applicability of this relationship.Vibration levelsVibration levels listed in Table 4 for the bus and the truck at 25and 50 km/h before road resurfacing were substantially higherthan the ISO 2631/2 guide value of 0.001g (rms). The correspondingvibration levels after the road was resurfaced weresignificantly reduced, as can be seen from the values listed inTable 5. For the truck, vibration levels became lower than theguide value at all points inside the building. For the bus at50 km/h, however, vibration levels in the second storey remainedhigher than the guide value by about 50% (vibrationlevels were six times the ambient acceleration levels of0.24 × 10 –3 g (rms))! Tenants might continue to complain inview of past experience by the City of Montréal that for somesites vibration complaints persisted even after the road wasresurfaced.It is interesting to note that vibration levels induced by theempty bus at 50 km/h (both before and after the road wasresurfaced) were similar to and in some cases higher than thecorresponding vibration levels induced by the loaded bus. Thesame trend was observed earlier by Al-Hunaidi and Rainer(1991) using an empty and a loaded water truck and by Watts(1990) using empty and loaded trucks. Also worth noting inTable 4 is that vibration levels induced by the bus and the truckat a speed of 25 km/h before the road was resurfaced weresimilar. At 50 km/h, however, vibrations induced by the buswere more than two times those induced by the truck. Obviously,the relationship between vehicle speed and vibrationlevels depends on the vehicle characteristics.Effect of seasonal variations in soilconditionsSoil conditions at complaint sites, particularly the frost layer inwinter and the level of ground water table, are believed toinfluence the level of traffic-induced vibrations. However, theextent of this influence is not clear. In a study of vibrationsinduced by buses in Winnipeg, Sutherland (1950) reported thatvibrations measured in winter while the top soil was frozenwere significantly less than those measured in summer.On theother hand, subway-induced vibrations in buildings that weremeasured more recently in Toronto were found to be slightlyhigher in winter (while the top soil was frozen) than in summer.1 Tests were performed in this study to determine the trendfor conditions in Montréal.Officials of many cities in Canada indicate that vibrationcomplaints are more frequent during the thaw period in springthan in other seasons. The extent to which the higher level ofground water table in the spring thaw period adversely affectvibration levels was not known. Tests were thus performed inthis study to shed some light on this issue.Description of testsTests were performed at site 9 after the road was resurfaced.Identical measurements of vibrations induced by a test buswere made during the fall, winter, and spring. Visual inspectionof the road surface at time of measurements in the differentseasons indicated that the road condition was almost identical.Tests were performed using a bus while empty and loaded; notrucks were used. The test bus was driven at speeds of 25 and50 km/h with and without a wood plank attached to the roadsurface. The wood plank was 3.7 cm high, 13.8 cm wide, and90 cm long. Only the far side of the bus passed over the woodplank located as shown in Fig. 6. Only the results obtainedwith the wood plank attached to the road are presented here;vibration levels for tests performed with no wood plank werelow and consequently the ratios between vibration levels in the1Bracken, M. 1994. Aercoustics Engineering Limited, Rexdale,Ont., Private communication.© 1997 NRC Canada

748Can. J. Civ. Eng. Vol. 24, 1997Table 7. Frequency-weighted vertical accelerations (10 -3 g, rms) induced by test buses in fall, winter, and spring.25 km/h 50 km/hEmpty bus Loaded bus Empty bus Loaded busLocation Fall Winter Spring Fall Winter Spring Fall Winter Spring Fall Winter SpringGround 3.66 1.56 3.86 3.87 1.72 3.78 4.18 1.92 3.94 4.25 1.63 4.22External foundation wall 2.47 1.21 2.57 2.61 1.26 2.48 2.58 1.14 2.47 2.66 1.03 2.92Midpoint of floor in 1st storey 3.49 1.89 3.99 3.68 2.04 4.08 3.80 2.04 4.34 4.17 1.93 5.05Midpoint of floor in 2nd storey 6.91 3.26 8.53 7.68 3.57 9.39 7.71 3.83 10.24 9.15 4.04 11.33Table 8. Ratio between bus-induced accelerations in winter and fall (winter/fall).25 km/h 50 km/hLocation Empty bus Loaded bus Empty bus Loaded busGround 0.42 0.44 0.46 0.38External foundation wall 0.49 0.48 0.44 0.39Midpoint of floor in 1st storey 0.54 0.55 0.54 0.46Midpoint of floor in 2nd storey 0.47 0.46 0.50 0.44Fig. 7. Vertical response and coherence functions obtained with thedrop weight device in summer and winter for the ground in front ofbuilding at site 9.Fig. 8. Narrow-band frequency spectra of acceleration recorded in(a) fall and (b) winter on ground in front of building at site 9(empty bus at 50 km/h).various seasons were not believed to be accurate. During alltests, the road and the nearest cross road north of the test buildingwere closed to public traffic.At the time of vibration measurements during winter, thetemperature was about –5°C and the depth of top frozen soilwas about 1.1 m, as found from both a soil borehole and a Cityof Montréal frost gauge at the site. Vibration measurements inthe spring were performed during the period when the groundwater table level was believed to be highest. At the time ofvibration measurements in the fall and spring, the level of theground water table was 5.8 and 2 m below the surface, respectively.Tests were also performed with the drop weight device inwinter and spring. No similar tests were performed in the fall,however, due to a device malfunction; instead, the results obtainedduring summer in earlier tests are used, assuming thatthe levels of the ground water table were similar at the time of© 1997 NRC Canada

Hunaidi and Tremblay 749Fig. 9. Vertical response and coherence functions obtained with thedrop weight device in summer and spring for the ground in front ofbuilding at site 9.measurements in summer and fall. Site response functions obtainedwith the drop weight device were used as an additionalsource of information on the effect of the frost layer and variationin ground water table level.Frozen soil samples were obtained at a depth of about 0.6to 0.8 m in front of the building at the time of winter tests.Dynamic shear moduli and damping ratios of the soil sampleswhile frozen and after they were allowed to thaw were determinedfrom resonant column tests (Al-Hunaidi et al. 1996b).Fall versus winter vibration levelsVibration levels and ratios obtained during the fall and winterare listed in Tables 7 and 8, respectively. Vibration levelsmeasured in winter were about one half those measured in thefall. This is in agreement with the results reported by Sutherland(1950) for similar vibration measurements in Winnipeg.Ratios of vibrations measured by Sutherland (1950) were generallyhigher than those found in this study. This is believed tobe due to the depth of the frost layer during Sutherland’s measurementsbeing 0.9 m, compared with 1.1 m in this study, and(or) due to the dominant frequency at the site of Sutherland’smeasurements in Winnipeg being about 7.5 Hz, comparedwith 13 Hz in this study.Vertical response and coherence functions obtained withten load impacts using the drop weight device during summerand winter are shown in Fig. 7 for the ground measurementlocations. The coherence is close to 1 over the frequency rangethat is of interest regarding traffic vibrations, i.e., 8–20 Hz,thus indicating a high signal-to-noise ratio. In this frequencyrange, it can be seen that the response function obtained insummer is higher than that obtained in the winter. This is consistentwith the results obtained using the test bus. For frequencieshigher than about 40 Hz, however, the response functionobtained in winter has higher magnitudes than that obtained inthe summer. This seems to corroborate the observation mentionedearlier that subway-induced building vibrations inToronto are higher in winter than in summer, as the dominantfrequency of these vibrations is between 40 and 50 Hz.Results of resonant column tests on frozen and unfrozensoil samples taken at the site used in this study show that thestiffness of soil samples while frozen is about 30–50 times thestiffness after they were allowed to thaw. In addition, thedamping ratio obtained with frozen samples was roughly twotimes that obtained with thawed samples. Apparently the increasein stiffness and damping of the top part of the soil ledto smaller vibrations (i.e., smaller dynamic deformations) forfrequencies up to 30 Hz. On the other hand, the increase instiffness of the top frozen part of the soil has led to a majorshift for the dominant frequency in the site response.Finally, it was observed that the range of predominantfrequencies of vibrations measured in the fall was widerthan the frequency range of vibrations measured in thewinter, i.e., the former had higher levels at higher frequencies(e.g., 20–30 Hz). This can be seen, for example,from the narrow-band spectra shown in Fig. 8. The followingmay provide the reason. Attenuation of vibrations in soils, dueto material damping only, along the direction of wave propagation,can be expressed as follows (Richart et al. 1970):[1] A 2 = A 1 exp[–α(r 2 – r 1 )]where A 1 and A 2 are vibration amplitudes at distances r 1 and r 2from the vibration source, respectively; α is the coefficient ofattenuation which is related to the soil damping ratio and frequencyof vibration by[2] α= 2πfDcwhere f is frequency, D is damping ratio, and c is wave propagationvelocity. Because of the exponent in the above attenuationrelationship, a higher damping ratio in winter will lead togreater attenuation at high frequencies than at low ones.Spring versus fall vibration levelsVibration levels and ratios obtained during the spring and fallare listed in Tables 7 and 9, respectively. Vibration levelsmeasured during the thaw period in spring were only slightlyhigher than those measured in the fall. The highest ratio of 1.33occurred in the second storey.The increase in vibration levels in the spring is not as highas expected, considering that more vibration complaints areusually made during this season. Possibly, the water table levelat the time of vibration measurements made in the spring wasnot as high as usual during the snow thaw period. On the otherhand, it might be speculated that the higher number ofcomplaints in the spring is in fact due to the significantly lowervibration levels during winter. The “quiet” winter period mightbe leading to a loss of familiarity with vibration and subsequentlyleading to a decrease in tolerance as vibration levelsincrease again in the spring.Vertical response and coherence functions obtained withthe drop weight device in summer and spring are shown inFig. 9 for the ground measurement locations. The coherence© 1997 NRC Canada

750Can. J. Civ. Eng. Vol. 24, 1997Table 9. Ratio between bus-induced accelerations in spring and fall (spring/fall).25 km/h 50 km/hLocation Empty bus Loaded bus Empty bus Loaded busGround 1.05 0.98 0.94 0.99External foundation wall 1.04 0.95 0.96 1.10Midpoint of floor in 1st storey 1.14 1.11 1.14 1.21Midpoint of floor in 2nd storey 1.24 1.22 1.33 1.24Table 10. Peak particle velocities in basementsinduced by test buses at 50 km/h.Peak velocity (mm/s)Site No. Vertical Transverse2 0.89 —3 0.80 —4 0.62 0.205 1.55 0.266 0.25 0.277 0.79 0.169 2.23 0.71is close to 1 over the frequency range of interest, i.e., 8–20 Hz,thus indicating a high signal-to-noise ratio. In this frequencyrange, the response function of the ground obtained in thespring is similar to or slightly lower than that obtained in summer.This trend is in agreement with the ratios listed in Table10, although drop weight tests performed in the summerwere used as a substitute for those that could not be performedin the fall.Human response to vibrationVibrations in buildings may be unacceptable to building tenantsfor one or more of the following reasons: annoying physicalsensations that vibration may produce in the human body;interference with activities such as sleep, conversation, andwork; annoying noise caused by “rattling” of window panes,walls, and loose objects; fear of damage to the building and itscontents; and interference with proper operation of sensitiveinstruments and (or) processes. For vibrations induced in residentialbuildings by road traffic, experience has shown thattenants are likely to complain if vibration levels are onlyslightly above the perception threshold — the major concernbeing fear of damage to the building or its contents. Withinresidential areas, existing vibration standards report that thereis a wide variation in vibration tolerance. Possibly, this iscaused by variation of the perception threshold and differencesin psychosocial and socioeconomic conditions among individuals.The International Organization for Standardization (ISO)and several countries have published standards that provideguidance for evaluation of human response to continuous, intermittent,and transient vibrations in buildings. Tentativeguidance is provided in the standards regarding satisfactoryvibration levels, i.e., levels at which adverse comment maybegin to arise or levels below which the probability of reactionis low. No such standards have yet been adopted in Canada.Three standards were used to evaluate human response to thevibration levels measured for transit buses in this study. Theyincluded standards published by the International StandardizationOrganization (ISO 1989), and standards organizationsin Britain (BSI 1984) and the United States (ASA 1983).Review of the above standards, details on evaluation ofvibration levels measured in this study, and recommendationsfor evaluation methods were reported by Al-Hunaidi (1996).It was found that the guidance provided by the standards is notclear when used for evaluation of vibrations induced by transitbuses. Bus-induced vibrations have relatively short durationand complex amplitude characteristics. The standards, however,seem to be geared for evaluation of continuous and intermittentvibrations such as that induced by machinery andpile driving, and impulsive vibrations such as that induced byblasting.The following two major difficulties were encountered inapplying the standards. First, there was confusion regardingthe classification of these vibrations, e.g., as intermittent ortransient vibrations. Both the ISO and American standardsmention vibrations induced by road traffic as examples forintermittent vibration, which in both standards is treated in thesame manner as continuous vibration. The British standardgives no examples; and it groups intermittent and transientvibrations under the same category. Vibration guide valuesprovided by the standards depend on the category of vibration.Second, although vibration levels are provided in the standardsin terms of rms values, there is no specification regarding theintegration time for rms calculation. For vibration signals withshort time duration and time-varying amplitude, which is thecase for vibrations induced by buses, rms values are significantlyinfluenced by the integration time. For impulsive signals,the American standard suggests using the peak method.The British standard offers the peak, root-mean-quad (rmq),and vibration dose value (VDV) as alternative methods forevaluation of transient signals. The ISO standard identifiesthese methods, but it is not clear whether it intended to recommendthem as alternative methods. This aspect of the variousstandards was confusing.In order to determine an appropriate method for the evaluationof vibration signals measured in this study, vibrationswere analysed using the following methods (Al-Hunaidi1996): (i) rms method, (ii) rmq method, (iii) peak method, and(iv) VDV method. Two sets of integration time were used forrms and rmq calculations. Also, vibration was evaluated asboth continuous and transient with several occurrences perday. Subsequently, the following two evaluation methods wereidentified as the most appropriate (Al-Hunaidi 1996), in viewof the measured vibration levels and complaints at the selectedsites:• Method I: rms or rmq acceleration evaluated with respectto the base value of 0.005 m/s 2 specified by ISO 2631/2 (ISO© 1997 NRC Canada

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

752resurfacing and seasonal variation in soil conditions on vibrationlevels. The major findings of the study were as follows:1. Transfer functions varied from one site to another, insome cases significantly. For rough prediction of vibration levelsinside buildings, it was suggested that first floor vibrationlevels be taken equal to those on the ground close to buildingsand that floor-to-floor amplification be taken as 2 times.2. Vibration levels induced by transit buses were at leasttwice those induced by trucks of the same weight category.Predominant frequencies of bus-induced vibrations were between10 and 12.5 Hz, while those of truck-induced vibrationsspread over a wider range.3. Each measurement site exhibited a “cutoff frequency”below which acceleration levels were very small. The lowestobserved cutoff frequency was 6.5 Hz.4. Road resurfacing resulted in a reduction of vibration levelsby a factor of at least 6.4. Although such a reduction factormight be sufficient to resolve vibration complaints at mostsites, second-storey vibration remained slightly higher thansatisfactory level for the selected site.5. Vibration levels measured while top soil was frozen inwinter were about one half those measured while the soil wasnot frozen.6. The effect of the level of the ground water table on vibrationlevels was not significant.7. Existing vibration standards for evaluation of human annoyancewere not clear when applied for bus-induced vibrations.Consequently, two evaluation methods were developedbased on measurements made in this study.8. Bus-induced vibrations were significantly lower than themost stringent guide value for building damage specified byexisting standards. The potential of traffic vibration for buildingdamage was therefore considered very small for the conditionsin Montréal.The cutoff frequency phenomenon and the finding that businducedvibrations are mainly due to axle hop have practicalsignificance. Possibly, vibration levels induced by buses — themain cause of vibration complaints in Montréal — could besignificantly reduced by modifications to bus suspension systems.Such modifications would consist of altering the axlehop frequency so that it is below the cutoff frequency of mostsites in the city and (or) reducing the axle hop amplitude andthe unsprung mass. Lighter urban transit buses, currently underdevelopment, offer some hope for a lighter unsprung mass.AcknowledgmentsThis study was carried out on a cost-sharing basis between theCity of Montréal and the Institute for Research in Construction,National Research Council of Canada (IRC/NRC). Theauthors would like to thank Dr. G. Pernica, Messrs. L. Wang,R. Glazer, T. Hoogeveen, and A. Laberge of IRC/NRC and Mr.C. Sanfaçon of the City of Montréal for their help in field testsand data processing. The authors would also like to expresstheir appreciation to J.H. Rainer of IRC/NRC for his manyhelpful comments. The cooperation of the regional PublicWorks Departments of the City of Montréal in arranging thetests and Société de transport de la Communauté urbaine deMontréal for providing test buses is gratefully acknowledged.Also, the cooperation of tenants and owners of buildings usedin the study is greatly appreciated.ReferencesCan. J. Civ. Eng. Vol. 24, 1997Al-Hunaidi, M.O. 1996. Evaluation of human response to buildingvibration caused by transit buses. Journal of Low Frequency Noiseand Vibration, 15(1): 25–42.Al-Hunaidi, M.O., and Guan, W. 1996. Digital frequency weightingfilters for evaluation of human exposure to building vibration.Noise Control Engineering Journal, 44: 79–91.Al-Hunaidi, M.O., and Rainer, J.H. 1990. 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