RESEARCH ON ASSESSMENT OF FOURTH POWER VIBRATION DOSE VALUE IN ENVIRONMENTAL VIBRA- TION CAUSED BY METRO

Transcription

1 The 2 st International Congress on Sound and Vibration 3-7 July, 204, Beijing/China RESEARCH ON ASSESSMENT OF FOURTH POWER VIBRATION DOSE VALUE IN ENVIRONMENTAL VIBRA- TION CAUSED BY METRO Yiqian Yang, Penghui Liu and Jing Yin Railway Engineering Research Institute, China Academy of Railway Sciences, Beijing, China yqyang@yeah.net With the rapid development of modern industry and the expanding of city scale in China, the environmental vibration which is caused by metro has been paid more and more attention. Because the environmental vibration during operation of metro is long-time and intermittent, and has high crest factor in daytime and nighttime, the basic evaluation method based on frequency-weighted r.m. acceleration may underestimate the effects of vibration. The fourth power vibration dose method is more sensitive to vibration peaks by using the fourth power instead of the second power of the acceleration time history as the basis for average and considers duration of human exposure to vibration. The evaluation of environmental vibration caused by metro should append fourth power vibration dose method. The impact analysis of frequency weighting network e.g. BS 684:987, ISO 263-:985 and ISO 263-:997, crest factor is studied, and vibration dose value (VDV) is gained considering number of metro train, time interval, duration of train passing in daytime and nighttime and type of track structure (monolithic track bed and steel spring floating slab track). Through comparison between fourth power vibration dose method and basic evaluation method using weighted r.m. acceleration, the VDV limit and method is given to assess environmental vibration caused by metro. For residential, the VDV limit is 0.2m/s.75 in daytime and 0. m/s.75 in nighttime.. Introduction With the rapid development of modern industry and the expanding of city scale in China, construction of urban rail transit has been rapid development. By the end of 203, there are 87 lines has been operated in 9 citie The total operation length has reached 2539 kilometre Because most of urban rail transit are located in the downtown, the environmental vibration and noise caused by metro is increasingly significant and attracts the public's strong attention, it becomes the primary factor restricting the development of urban rail transit system. Therefore, it puts forward new requirements about research on vibration caused by urban rail transit and the effect of the surrounding environment. Above of all, evaluation of environmental vibration effect, evaluation method, degree of vibration effect and vibration protection measures are problems concerned by international scholar Griffin, Howarth, Mansfield, etc. analyzed the human response to vibration by different physical quantities (acceleration and velocity), different assessment methods (running r.m. method, r.m. method and fourth power vibration dose method) and different frequency-weighting curves, researched evaluation of human body comfort and influence factors caused by rail vibration, proposed evaluation method of VDV -7. Yiqian Yang reviewed the whole-body vibration perception ICSV2, Beijing, China, 3-7 July 204

2 thresholds 8 ; Yiqian Yang, Jing Yin and Penghui Liu evaluated human comfort of vibration in elevated over-crossing and low-lying waiting hall 9-0. In most of the countries in the world, the standards of environmental vibration and evaluation of human exposure to vibration in buildings are based on basic evaluation method using frequencyweighted r.m. acceleration. Because the environmental vibration caused by metro is long-time and intermittent, and has high crest factor in daytime and nighttime, the basic evaluation method may underestimate the effects of vibration to human comfort. Besides, it also does not consider duration of human exposure to vibration. Based on the above reasons, the evaluation of effects of vibration to human comfort in buildings caused by metro should append fourth power vibration dose method. Based on the vibration test data of Beijing subway line 4 in different distance on the ground, the impact analysis of frequency weighting curve, crest factor is studied, and vibration dose value (VDV) is calculated and discussed considering number of metro train, time interval, duration of train passing in daytime and nighttime and type of track structure. Table. Comparison between international and British standards of vibration evaluation Track structure type Monolithic track bed Steel spring floating slab track Buried depth of tunnel 29.5m 26.3m Cross section form of tunnel Round, single hole, single line Speed of train 60km/h Frequency-weighting curve BS 684:987, ISO263-:985, ISO263-:997 Horizontal distance 0m and 65m 2. Standards ISO/TC 08 has began to study evaluation of human exposure to whole-body vibration since 964. In 978, the first edition of ISO 263 was published. Then through draft and revise, ISO issued the standards ISO 263-:985 and ISO 263-:997 2 respectively. This standard is basic of evaluation of human exposure to whole-body vibration. Besides of basic evaluation method using frequency-weighted r.m. acceleration, there are two additional evaluation methods which are running r.m. method using maximum transient vibration value (MTVV) and fourth power vibration dose method using vibration dose value (VDV). According to their own situation, various countries developed relevant evaluation standard for environmental vibration. Most limit value of environmental vibration and human exposure to whole-body vibration in buildings derives from the perception thresholds, but a few derives from acceptable degree of annoyance by field study of relationship between exposure and reaction of human. Table 2 lists the international and British standards of vibration evaluation. Table 2. Comparison between international and British standards of vibration evaluation Standard ISO 263:-997 ISO 263: BS 6472:-2008 Evaluation method Basic a r.m. Additional MTVV and VDV VDV Frequency range (Hz) ~80 0.5~80 Frequency-weighting curve ISO 263:-997 BS 684:987 Time constant (s) The guidance curves that were set in ISO 263-2:989 3 are no longer present in ISO 263-2: However, they may be still used in a few countries, for instance in Sweden and in the USA (at the stage Detailed Analysis) 5. In these specifications, the multiplying factors of residential are 2 to 4 in daytime and.4 in nighttime for continuous or intermittent vibration. ICSV2, Beijing, China, 3-7 July 204 2

3 BS 6472:984 6, BS 684:987 7, ISO 263-2:989 and ISO263-:997 put forward the VDV concepts and definition The above standards point out basic evaluation method using frequency weighted r.m. acceleration may underestimate the effects of vibration in three conditions: ) crest factor is more than 9 (ISO 263-:997) or more than 6 (BS 684:987); 2) intermittent vibration or occasional shocks when crest factor is less than 9 (or less than 6); 3) transient vibration. In the above situation, or there is doubt even if it does not belong to the above situation, should append fourth power vibration dose method. BS 6472:992 8 first proposed the permissible VDV of human response to vibration in buildings, and took the railway environmental vibration for example to calculate VDV. BS : supersedes the BS 6472:992 except the blasting vibration source, only adopts vibration dose method to assess, abandons the basic evaluation method, and modifies VDV. The fourth power vibration dose method is more sensitive to vibration peaks by using the fourth power instead of the second power of the acceleration time history as the basis for average and considers duration of human exposure to vibration. VDV given by BS 6472-:2008 is shown in Table 3. In Australia, Assessing Vibration: a Technical Guideline points out that VDV should be adopted when evaluating the intermittent vibration 20. Table 3. VDV ranges which might result in various probabilities of adverse comment within buildings Place Time Low probability of Adverse comment adverse comment(m/s.75 ) possible(m/s.75 ) 6 h day 0.2 to to to.6 8 h night 0. to to to 0.8 adverse comment probable(m/s.75 ) Residential buildings Offices 6 h day 0.4 to to.6.6 to 3.2 Workshops 6 h day 0.8 to.6.6 to to Assessment of environmental vibration caused by metro The operation time of Beijing subway line 4 is from 5:00 to 24:00 generally, which departure intervals is between 2min and 0min in single direction. The train number in different time is shown in Fig.. There are about total 636 trains during daytime (6:00 to 22:00) and 32 trains during nighttime (22:00 to 6:00) in both line 8:00 to 9:00 is morning rush hour and 7:00 to 8:00 is evening rush hour. Figure 2 shows the acceleration time-domain waveform of environmental vibration on the ground where the horizontal distance is 65m from the centre of line. The vibration is intermittent and the duration of ground vibration caused by single train is about 0 It cannot be ignored that the cumulative duration of vibration caused by bidirectional trains during one day can reach 9% of total operating time (8h). Number of train Figure. The number of train in different time. Acceleration (m/s 2 ) Time (s) Figure 2. Acceleration time-domain waveform of environmental vibration on the ground ICSV2, Beijing, China, 3-7 July 204 3

4 3. Crest factor Crest factor, as shown in Fig. 3, is the ratio of vibration acceleration peak value to r.m. value with the same frequency-weighting curve in a measuring cycle. Table 4 shows the crest factors of environmental vibration on the ground caused by metro during different time. The horizontal distance to the centre of line is 65m. The crest factor during train passing is about 4.. The crest factor during train passing and interval is about 4.9. For daytime (6h) and nighttime (8h), crest factor is about 9.9 and 7.3 respectively. Acceleration (m/s 2 ) Peak a r.m Time (s) Figure 3. Vibration acceleration peak and r.m. with frequency-weighting curve of ISO 263-:997 Table 4. Crest factor of environmental vibration on the ground caused by metro Time Peak(0-3 m/s 2 ) a (0-3 m/s 2 ) Crest factor The background vibration (no train) Single train passing (0s) Single train passing (0s) + interval (20s) Daytime (6h) Nighttime (8h) Frequency-weighting curves Most standards related to evaluation of human exposure to vibration in buildings take acceleration to evaluate, but adopt different frequency-weighting curve At present, the frequencyweighting curves mainly come from the following criteria: ISO 263-:985, ISO 263-:997 and BS 684:987. The frequency-weighting curves of different standards are shown in Fig. 4. For environmental vibration caused by metro, the vertical evdv with frequency-weighting curves of BS 684:987 is.8 and.3 times as much as ISO 263-:985 and ISO 263-:997 respectively. 5 5 Wweighting curves (db) ISO263-:985 BS684:987 ISO263-:997 0 Frequency (Hz) 00 Weighting curves (db) ISO263-:985 BS684:987 ISO263-:997 0 Frequency (Hz) 00 (a) Vertical (b) Horizontal Figure 4. The frequency-weighting curves of different standard 3.3 alculation of VDV VDV is more sensitive to vibration peaks by using the fourth power of the acceleration time history as the basis for average and considers duration of human exposure to vibration. ICSV2, Beijing, China, 3-7 July 204 4

5 T 4 VDV aw ( t) dt 0 Where: a w (t) is the instantaneous frequency-weighted acceleration. T is the duration of measurement. For continuous vibration which is not time-varying in magnitude and has a crest factor which is between about 3 and 6, an approximation to the VDV may be determined from the estimated vibration dose value (evdv). The definition is: evdv ICSV2, Beijing, China, 3-7 July () / 4.4ar. m. T (2) When the vibration exposure consists of N vibration episodes of various durations each with a vibration dose value of VDV i, the VDV for the total exposure is: N 4 4 VDVi (3) i VDVtotal When the vibration exposure consists of N repeating vibration episodes each with a same vibration dose value of VDV, the VDV for the total exposure is: 0.25 VDV N VDV (4) It should be pointed out that the frequency-weighting curves of BS 6472:992 and BS :2008 is from BS 684:987, which is different from ISO 263-:985 and ISO 263-:997. In addition, the time period of BS 6472:992 and BS :2008 is 7:00~23:00 for daytime and 23:00~7:00 for nighttime, but it is 6:00~22:00 for daytime and 22:00~6:00 for nighttime in China. Comparison between VDV and evdv of environmental vibration by metro is listed in Table 5. The evdv is slightly less than VDV. Crest factor is between 4 and 5 when trains passing through, therefore, evdv of duration when trains passing is suitable and can be instead of VDV approximatively. For Beijing subway line 4, the VDV on the ground where the horizontal distance is 65m from the centre of line is m/s.75 in daytime (6h) and 0.0 m/s.75 in nighttime (8h). Table 5. Comparison between VDV and evdv (ISO 263-:997, monolithic track bed, 65m) Number of trains VDV(m/s.75 ) evdv(m/s.75 ) (6 h day) (VDV) d,6h =0.023 (evdv) d,6h = (8 h night) (VDV) n,8h =0.0 (evdv) n,8h = Environmental vibration caused by metro in three direction Figure 5 shows frequency-weighted r.m. acceleration of environmental vibration in three directions (X is lateral direction of line, Y is longitudinal direction of line, Z is vertical) on the ground where the distance to centre of line is 65m. Table 6 shows the ground evdv in three directions with frequency-weighting curves of ISO 263:997. The vertical evdv z of single train is 3 to 7.5 times as much as evdv x and evdv y. Therefore, only vertical vibration is analyzed and evaluated on environmental vibration caused by metro. a r.m. (0-3 m/s 2 ) X-direction Y-direction Z-direction Time (s) Figure 5. The r.m. acceleration of environmental vibration on the ground in three direction

6 Table 6. evdv of environmental vibration in three directions caused by metro Track structure evdv x (m/s.75 ) evdv y (m/s.75 ) evdv z (m/s.75 ) Monolithic track bed Steel spring floating slab track evdv of different track structure and frequency-weighting curve On the ground where the horizontal distance is 0m and 65m from the centre of line, the evdv of monolithic track bed and steel spring floating slab track using different frequency-weighting curves is shown in Table 7. Figure 6 and Figure 7 are comparison of evdv where the distance to centre of line is 0m in different time of daytime and nighttime respectively. There is no train from 24:00 to 5:00, so the line of evdv is level. The evdv of steel spring floating slab track, with the same frequency-weighting curve, is 2~30% of monolithic track bed. Table 7. evdv of environmental vibration on the ground using different frequency-weighting curves Number of Distance evdv of monolithic track bed evdv of steel spring floating slab track (m/s.75 ) (m/s.75 ) trains (m) ISO 263-:985 ISO 263-:997 BS 684:987 ISO 263-:985 ISO 263-:997 BS 684: (6h day) (8h night) (6h day) (8h night) evdv (m/s.75 ) ISO 263-:985 ISO 263-:997 BS 684:987 evdv (m/s.75 ) ISO 263-:985 ISO 263-:997 BS 684: evdv (m/s.75 ) :00 7:00 8:00 9:00 0:00 :00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 20:00 2:00 22:00 22:00 23:00 0:00 :00 2:00 (a) daytime (b) nighttime Figure 6. Comparison of evdv of monolithic track bed in different time. ISO 263-:985 ISO 263-:997 BS 684:987 evdv (m/s.75 ) :00 ISO 263-:985 ISO 263-:997 BS 684:987 4:00 5:00 6: :00 7:00 8:00 9:00 0:00 :00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 20:00 2:00 22:00 22:00 23:00 0:00 :00 2:00 (a) daytime (b) nighttime Figure 7. Comparison of evdv of steel spring floating slab track in different time. The classification of buildings and VDV limits of environmental vibration caused by metro is according to BS 6472-:2008 while frequency-weighting curve adopts ISO 263-:997. For resi- 3:00 4:00 5:00 6:00 ICSV2, Beijing, China, 3-7 July 204 6

7 dential buildings, the VDV limits of environmental vibration caused by metro are 0.2 m/s.75 in daytime (6 h) and 0. m/s.75 in nighttime (8 h). For monolithic track bed and steel spring floating slab track, vibration r.m. acceleration corresponding to the VDV limits of different exposure time is shown in Fig. 8. The maximum of evdv on the ground during 6 h in daytime and 8 h in nighttime are m/s.75 and 0.03 m/s.75 respectively, and both of them are lower than corresponding limit. Due to vibration attenuation in the buildings than outdoor, VDV in buildings caused by metro will be much less than the above limit. According to Eq. (2): evdv ar. m. (5) ( nt ) Where: T is the passing time of single train. n is the number of trains in an exposure period. a is the frequency-weighted r.m. acceleration. For daytime (6 h, 636 trains), If evdv = 0.2 m/s.75, a =0.2/.4/(636 0) 0.25 = 0.06 m/s 2. For environmental vibration of metro, the vertical evdv with frequency-weighting curves of BS 684:987 is.8 times as much as ISO 263-:985. Therefore, a with frequency-weighting curves of BS 684:987 is m/s 2 which is slightly less than the limit of 0.0~0.02 m/s 2 in daytime of ISO 263-2:989 (multiplying factor is 2~4). For nighttime (8 h, 32 trains), If evdv = 0. m/s.75, a =0./.4/(32 0) 0.25 = 0.07 m/s 2. With frequency-weighting curves of BS 684:987, a is m/s 2 which is slightly higher than the limit of m/s 2 in nighttime of ISO 263-2:989 (multiplying factor is.4). Standards for Allowable Vibration of Building Engineering (GB ) in China specify evaluation on environmental vibration caused by traffic should append VDV Acceleration r.m.(m/s 2 ) h, 65m 8h, 65m 6h, 0m 8h, 0m VDV (m/s.75 ) Acceleration r.m.(m/s 2 ) h, 65m 8h, 65m 6h, 0m 8h, 0m VDV (m/s.75 ) Exposure time (s) Exposure time (s) (a) monolithic track bed (b) steel spring floating slab track Figure 8. Vibration r.m. acceleration corresponding to the VDV limits of different exposure time. 4. Conclusion Due to environmental vibration during operation of metro is long-time and intermittent, and has high crest factor of 9.9 in daytime and 7.3 in nighttime, the basic evaluation method based on frequency-weighted r.m. acceleration may underestimate the effects of vibration. The evaluation of environmental vibration caused by metro should append fourth power vibration dose method. According to BS 6472-:2008, for residential buildings, the VDV limits of environmental vibration caused by metro are 0.2 m/s.75 in daytime (6 h) and 0. m/s.75 in nighttime (8 h). Adopting frequency-weighting curve of ISO 263-:997 from Hz to 80 Hz, the maximum of evdv on the ground during 6 h in daytime and 8 h in nighttime are m/s.75 and 0.03 m/s.75 respectively. Both of them are lower than corresponding limit. Due to vibration attenuation in the buildings than outdoor, VDV in buildings caused by metro will be much less than the above limit. ICSV2, Beijing, China, 3-7 July 204 7

8 Standards for Allowable Vibration of Building Engineering (GB ) in China specify evaluation on environmental vibration caused by traffic should append VDV. REFERENCES Griffin, M.J., Whitham, E.M., Discomfort Produced by Impulsive Whole Body Vibration, Journal of the Acoustical Society of America, 68, , (980). 2 Howarth, H.V.C., Whitham, E.M., Human Response to Simulated Intermittent Railway Induced Building Vibration, Journal of Sound and Vibration, 20(2), , (988). 3 Griffin, M.J., SAE Paper , Evaluation of Vibration with Respect to Human Response, (986). 4 Howarth, H.V.C., Griffin, M.J., The Relative Importance of Noise and Vibration from Railways, Applied Ergonomics, 2(2), 29 34, (990). 5 Howarth, H.V.C., Griffin, M.J., The Annoyance Caused by Simultaneous Noise and Vibration from Railways, Journal of the Acoustical Society of American, 89(5), , (99). 6 Griffin, M.J., Handbook of Human Vibration, Academic Press, London/New York, (990). 7 Mansfield, N.J., Human Response to Vibration, CRC Press, Boca Raton, (2005). 8 Yang, Y.Q., Whole-body Vibration Perception Threshold, Journal of the Architecture & Environmental Engineering, 34, 54 60, (202). 9 Yang, Y.Q., Yin, J., Liu, P.H., Test and Evaluation of Vibration Environment in Elevated Over-crossing Waiting Hall of High-speed Railway, Proceedings of the 20 th International Congress on Sound and Vibration, Bangkok, Thailand, 7- July, (203). 0 Yin, J., Yang, Y.Q., Liu, P.H., Test and Evaluation of Vibration Environment in Low-lying Waiting Hall of High-speed Railway, Proceedings of the 6 th International Symposium on Environment Vibration, Shanghai, China, 8-0 Nov, (203). ISO 263-:985, Evaluation of Human Exposure to Whole-body Vibration-Part : General Requirement 2 ISO 263-:997, Mechanical Vibration and Shock-Evaluation of Human Exposure to Whole-body Vibration-Part : General Requirement 3 ISO 263-2:989, Evaluation of Human Exposure to Whole-body Vibration-Part 2: Continuous and Shock-induced Vibration in Buildings ( to 80 Hz). 4 ISO 263-2:2003, Mechanical Vibration and Shock-Evaluation of Human Exposure to Whole-body Vibration-Part : Vibration in Buildings ( Hz to 80 Hz). 5 ANSI S , American National Standard Guide to the Evaluation of Human Exposure to Vibration in Building 6 BS 6472:984, Evaluation of Human Exposure to Vibration and Shock in Buildings ( Hz to 80 Hz). 7 BS 684:987, Guide to Measurement and Evaluation of Human Exposure to Whole-body Mechanical Vibration and Repeated Shock. 8 BS 6472:992, Guide to Evaluation of Human Exposure to Vibration in Buildings ( Hz to 80 Hz). 9 BS 6472-:2008, Guide to Evaluation of Human Exposure to Vibration in Buildings-Part : Vibration Sources Other Than Blasting. 20 Department of Environment and Conservation, Assessing Vibration: a Technical Guideline,, Sydney, (2006). 2 GB , Standards for Allowable Vibration of Building Engineering. 22 Yang Y.Q, Liu P.Y., Traffic Vibration Standards, Chapter 6, Understanding and Application of Standards for Allowable Vibration of Building Engineering, Xu J. ed., China Architecture & Building Press Beijing, (203). ICSV2, Beijing, China, 3-7 July 204 8