Field measurements and analyses of environmental vibrations induced by high-speed Maglev.

STOTEN-19225; No of Pages 13 Science of the Total Environment xxx (2016) xxx–xxx

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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Field measurements and analyses of environmental vibrations induced by high-speed Maglev Guo-Qiang Li a, Zhi-Lu Wang a,b, Suwen Chen a,⁎, You-Lin Xu b a b

College of Civil Engineering, Tongji University, Shanghai, China Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Environmental 3D vibrations induced by high-speed Maglev train were systematically measured. • Attenuation of ground vibration with distance up to 30 m was investigated. • Effects of train speed and guideway configuration were studied in time and frequency domains. • Vibrations induced by high-speed Maglev train and high-speed railway train are compared.

a r t i c l e

i n f o

Article history: Received 1 December 2015 Received in revised form 31 January 2016 Accepted 31 January 2016 Available online xxxx Keywords: Maglev Guideway configuration Three directional vibrations Pier vibration Ground vibration Time domain Frequency domain

a b s t r a c t Maglev, offers competitive journey-times compared to the railway and subway systems in markets for which distance between the stations is 100–1600 km owing to its high acceleration and speed; however, such systems may have excessive vibration. Field measurements of Maglev train-induced vibrations were therefore performed on the world's first commercial Maglev line in Shanghai, China. Seven test sections along the line were selected according to the operating conditions, covering speeds from 150 to 430 km/h. Acceleration responses of bridge pier and nearby ground were measured in three directions and analyzed in both the time and frequency domain. The effects of Maglev train speed on vibrations of the bridge pier and ground were studied in terms of their peak accelerations. Attenuation of ground vibration was investigated up to 30 m from the track centerline. Effects of guideway configuration were also analyzed based on the measurements through two different test sections with same train speed of 300 km/h. The results showed that peak accelerations exhibited a strong correlation with both train speed and distance off the track. Guideway configuration had a significant effect on transverse vibration, but a weak impact on vertical and longitudinal vibrations of both bridge pier and ground. Statistics indicated that, contrary to the commonly accepted theory and experience, vertical vibration is not always dominant: transverse and longitudinal vibrations should also be considered, particularly near turns in the track.

⁎ Corresponding author at: College of Civil Engineering, Tongji University, Shanghai, 200092, China. E-mail address: [email protected] (S. Chen).

http://dx.doi.org/10.1016/j.scitotenv.2016.01.212 0048-9697/© 2016 Elsevier B.V. All rights reserved.

Please cite this article as: Li, G.-Q., et al., Field measurements and analyses of environmental vibrations induced by high-speed Maglev, Sci Total Environ (2016), http://dx.doi.org/10.1016/j.scitotenv.2016.01.212

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G.-Q. Li et al. / Science of the Total Environment xxx (2016) xxx–xxx

Moreover, measurements of ground vibration induced by traditional high-speed railway train were carried out with the same testing devices in Bengbu in the Anhui Province. Results showed that the Maglev train generates significantly different vibration signatures as compared to the traditional high-speed train. The results obtained from this paper can provide good insights on the impact of Maglev system on the urban environment and the quality of human life nearby. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Magnetic levitation (Maglev) trains, with the non-contact and nonwearing levitation, guidance, and propulsion technology, is free of friction, making it feasible to reach very high speeds. Compared to the railway and subway systems, Maglev offers competitive journey-times in markets for which distance between the stations is 100–1600 km (US Federal Administration, 2001). Additionally, compared with conventional wheel-rail systems, advantages of a Maglev system also include lower risk of derailment, higher riding comfort, lower noise and less energy consumption (Lee et al., 2006; Yaghoubi, 2013). Several Maglev test lines have been built using two main types of systems: the electromagnetic suspension system (EMS) and the electrodynamic suspension system (EDS) (Yaghoubi and Rezvani, 2011), as shown in Table 1. Several Maglev lines, such as the Beijing S1 line, the Changsha Maglev line, the Shinkansen line, and the Tel Aviv line, are under construction. The Shanghai Maglev Line (SML) is the world's first commercial highspeed Maglev line. The length of the SML is 30 km, connecting the Shanghai Pudong Airport to the Longyang Railway Station. The construction of the SML began in March 2001, was tested on December 2002 and commenced commercial service on March 29, 2004. Subsequently, the SML has operated continuously for 12 years. In the past two decades, many research efforts have been carried out on Maglev systems. For example, a dynamic interaction model of a Maglev line with a multicar, multi-load train running over a flexible guideway was developed by Cai and Chen (1996). Dynamic characteristics, vertical motion and levitation stability of Maglev trains were analyzed and a stability criterion was developed by Tsunashima and Abe (1998) in terms of a 17-degrees of freedom (DOF) vehicle model considering a mechanical air gap control system. Based on the German Maglev Transrapid system, the Maglev vehicle response and ride comfort were investigated by Zhao and Zhai (2002) using a 10-DOF model of Maglev vehicle considering guideway irregularities. A 3D dynamic model of high-speed EMS Maglev vehicle/guideway interaction, regarding the vehicle and guideway as an integral system with coupled vertical and lateral vibrations, meantime, considering the vehicle subsystem as a multi-body and guideway substructure as elastic beam, was presented by Shi et al. (2007). Dynamic responses of a Maglev vehicle running over a series of guideway girders with support settlement and

Table 1 The maglev test lines in the world. Country

German

China

Japan

Japan

Korea

Line Type Length (km) Speed (km/h)

Emsland EMS 31.5 450

Shanghai EMS 30 501

JR EDS 42.8 603

HSST EMS 9 100

KIMM EMS 1.3 100

under cross-wind loads were also investigated in detail (Tamai, 2010; Yau, 2010; Yau, 2009). A 2D Maglev train-guideway-pier-soil system was presented and analyzed using an iterative method by Yang and Yau (2011). Moreover, the successful operation of Urban Transit Maglev (UTM-01) in South Korea pushed forward the development of medium and low speed Maglev trains (Doh et al., 2009). The use of a 3D finite element (FE) model of a Maglev vehicle gave the deformation of an elevated flexible guideway and the dynamic stress and the motion of the vehicle (Han et al., 2006). By combining an 11-DOF Maglev vehicle model with a cable-supported bridge finite element model, the dynamic behavior of the coupled Maglev vehicle-guideway-wind-bridge system was investigated (Kwon et al., 2008). A numerical model was also developed for a dynamic interaction analysis of an actively controlled Maglev vehicle and a flexible guideway structure to investigate the effects of vehicle speed, irregularity, guideway deflection ratio, span length, damping ratio and nonlinear electromagnetic forces (Lee et al., 2009; Min et al., 2012). To analyze the instability mechanism and investigate the air gap control performance, an integrated model, incorporating a 3D vehicle model, a flexible guideway and levitation electro-magnets with controller, was proposed by Kim et al. (2015). As demonstrated here, the majority of current research is directed toward vehicle operating principles, dynamics of the car body and bogie, and guideway analysis and design. Research on Maglev train-induced ground vibration has been limited. A 3D multi-body vehicle-guideway-soil finite element model was presented to study the ground vibration induced by a high-speed Maglev train running in a tunnel (Wang et al., 2011; Wang et al., 2012). A Maglev vehicle-bridge interaction model was proposed together with a finite element model of the pier foundation of a viaduct to obtain ground vibration responses (Zhao, 2010). Field vibration measurement was performed on the SML with the trains running at operational speeds of 150 km/h, 200 km/h, 250 km/h (Bi, 2015). The measurement data showed that the ground vibration induced by high-speed railway trains (HSRT) is quite different from that induced by high-speed Maglev trains. With the increase of Maglev train speed and the use of Maglev trains within urban settings, the Maglev train-induced ground vibration has raised concerns for the public, particularly with regard to office and residential buildings near Maglev lines. Surveys showed that the minimum distance from business areas to the SML is less than 30 m, in Zhangjiang Hi-Tech Park, where the requirement on micro-vibration is strict. Therefore, investigation of Maglev train-induced ground vibration is of paramount importance. To better understand Maglev train-induced vibrations, field tests were performed on the SML. Seven test sections along the SML were selected according to operating conditions. Acceleration responses of bridge piers and the nearby ground were measured in three directions. The attenuation of ground vibration with distance was investigated by measuring ground vibration up to 30 m from the track center-line.

Table 2 The key parameters of the maglev train used in the SML. Car type

Head car Middle car

Mc (kg)

Mb (kg)

Full

Empty

30,000 32,500

20,900 18,300

8000 8000

Jc (kg·m2) Full

Empty

1.80 × 106 1.95 × 106

1.25 × 106 1.10 × 106

Jb (kg·m2)

Kp (N/m)

Cp (N·s/m)

Ks (N/m)

Cs (N·s/m)

1.20 × 104 1.20 × 104

1.18 × 108 1.18 × 108

2.15 × 106 2.15 × 106

6.81 × 105 6.81 × 105

8.46 × 104 8.46 × 104



3

Fig. 1. The characteristic lengths of SMT.

Table 3 The specific characteristic lengths and frequencies of SMT at speed of 430 and 300 km/h. Train type

L1 (m)

L2 (m)

L3 (m)

L4 (m)

SMT Speed (km/h) 430 300

0.258 f1 (Hz) 463 323

3.096 f2 (Hz) 38.58 26.92

6.192 f3 (Hz) 19.29 13.46

24.500 f4 (Hz) 4.88 3.40

The measurement results for bridge pier and ground accelerations induced by HSMT at speeds varying from 150 to 430 km/h were analyzed. Effects of Maglev train speed on vibrations of both bridge piers and the ground were assessed in terms of their peak accelerations at a given test section. Effects of guideway configuration were also investigated by analyzing the measurement data when the Maglev train ran at a speed of 300 km/h through two different test sections. To compare with HSRTinduced ground vibration, in-situ experiments of a railway system with an operation speed of 300 km/h were carried out in Bengbu in the Anhui Province. 2. Shanghai Maglev system

Fig. 3. The geometry of girders used in SML.

of inertia of car body and bogie. Kp and Cp are the stiffness and damping of primary suspension of train (per suspension magnet); Ks and Cs are the stiffness and damping of secondary suspension of train (per suspension bogie). The periodic excitation frequencies under the repeated action of Maglev magnet force are mainly due to the fundamental frequencies f1, f2, f3 and f4 of pier and ground vibration generated by Maglev train, which are defined in Eq. (1) as fi ¼

Two Maglev trains running on the SML simultaneously in opposite directions, each 128 m long and composed of five carriages (Wu, 2003). The trains run on a 15–20 min intervals from 6:45 am to 21:40 pm with a top speed of 430 km/h during two periods from 9:00–10:45 am and 15:00–15:45 pm (Speed A) and 300 km/h during other periods (Speed B). The Maglev train, with a maximum acceleration of 0.9 m/s2, takes about 135 s to reach 300 km/h, and another 70 s to reach 430 km/h. Table 2 lists the key parameters for the SML Maglev train (Wu, 2003), in which Mc and Mb denote the mass of car body and suspension bogie frame, respectively; Jc and Jb are the moment

v i ¼ 1; 2; 3; 4 Li

ð1Þ

where fi is the characteristic frequency of pier and ground-borne vibrations induced by Maglev train (Hz); v represents Maglev train speed (m/s); Li is the characteristic lengths of train shown in Fig. 1. The characteristic lengths can be classified into 4 types: the center distance of adjacent ferrite cores (L1), the center distance of adjacent suspension magnets (L2), the center distance of adjacent bogies (L3), the center distance of two neighboring cars (L4). Table 3 lists the specific characteristic lengths of Shanghai Maglev train (SMT), together with characteristic frequencies of Maglev train at speed of 430 and 300 km/h. Similarly

Fig. 2. Elevated guideway with (a) single-column piers; (b) double-column piers.


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G.-Q. Li et al. / Science of the Total Environment xxx (2016) xxx–xxx Table 4 Site conditions of the test sites. Site

1

2

3

4

5

6

7

Pier No. Speed A (km/h) Speed B (km/h) Distance (m) Configurationa

0059 150 150 20 c

0116 215 215 20 c

0146 245 245 30 c

0238 315 300 20 c

0298 350 300 20 c

0499 430 300 30 s

0555 430 300 20 s

a

Fig. 4. Site conditions of SML.

Guideway configuration: 'c' represents curved route; 's' represents straight route.

3. Measurement arrangement 3.1. Measurement sections

with the wheel-rail train (Auersch, 2006; Kouroussis et al., 2014), the first dominant frequency is apparent due to the periodic excitation f1 of the magnet force generated by the ferrite core loading on the girder. The second dominant frequency has a strong correlation with the fundamental suspension magnets frequency f2. The third main frequency is due to the periodic excitation f3 associated with bogie passage. The fourth main frequency f4 is due to the periodic excitation of the gravity of the car body. As for the complex interaction mechanisms among the car bodies, suspension bogies, suspension magnets, girders, piers and other components inside the Maglev vehicle, the variances of frequencies occur in different test sites. The measured data in this test approximately follows the law proposed in the references (Auersch, 2006; Kouroussis et al., 2014) and will be analyzed in details in this paper. Two main types of elevated guideways serve the SML (Eberhard, 2002): (i) double-column piers with a center-to-center distance of 5.1 m for the main part of the SML; (ii) single-column piers with a center-to-center distance of 10 m for the rest part of the SML, as shown in Fig. 2. The surface height of the girders above the ground for the track sections is 8–11.5 m. The girders along the SML are primarily single-span guideways of 24.768 m length with ″I″-shape cross sections. Its geometry is detailed in Fig. 3. The SML has been protected with barriers, leaving 20–30 m of space for management and maintenance and for the safety of Maglev operation. A cement road having a width of 4 m was built at a distance of 5 m from the track centerline, as shown in Fig. 4. Additionally, the soil along the SML is composed of unconsolidated quaternary sediments covered with soft grass covered (Yan and Shi, 2006). According to GB50011-2010 and DGI08-37-2012, the site condition along SML belongs to Site Classification II on condition: equivalent shear wave velocity (250 b vse b 500 m/s) and thickness of site soil layer (d0 N 5 m).

To investigate the effects of Maglev train speed and distance on ground vibration, 7 measurement sections were selected, as shown in Fig. 5. Fig.5 also shows operation speeds of SMT along the line, as provided by the management company. The line conditions of the selected test sections are detailed in Table 4. Because of the iron barriers, the available test distance from the centerline of the SML is limited: some sites had 30 m, while other sites had only 20 m access. To reduce noise caused by other traffic or nearby construction sites, the test sections were selected to be at a distance of no less than 100 m from highway roads or construction sites. Fig. 6 presents the arrangement of measurement locations for site 6. Accelerometers were located according to a preset distance. A 3-axis accelerometer was fixed on the pier at 0.5 m above the ground and 3 single-axis accelerometers were fixed at each ground measuring point in three orthogonal directions. Both laser velocimeters and accelerometers were used in this test. Laser velocimeter (model: LRM 1500 SPD) was used to measure Maglev train speed, with a measurement range from 5 to 500 km/h (see Fig. 7 (a)). Two types of accelerometers were used in the test: LC0161 piezoelectric 3-axis accelerometer (sensitivity of 1000 mV/g and measuring range of 5 g) for the measurement of the pier vibration, and LC0155 piezoelectric single-axis accelerometer (sensitivity of 700 mV/g and measuring range of 7 g) for the measurement of the ground vibration. To measure ground vibration at a given point, a long angle-steel member was heavily tamped into soil, as shown in Fig. 7(b). A steel block was attached to the top of the member and three single-axis accelerometers were then installed on the steel block in three orthogonal directions, as shown in Fig. 7(c). To install the 3-axis accelerometer on the pier, an angle-steel member was first fixed on the concrete pier and the accelerometer was then installed on the member, as shown in Fig. 7(d).

Fig. 5. Arrangement of test sites and distribution of operation speed along the SML.



5

Fig. 6. Schematic diagram of measuring points at site 6.

Fig. 7(e) shows 32-channel dynamic data acquisition system (model: SIRIUS-HD STGS). The sampling frequency used in this test is 1500 Hz. Fig. 7(f) shows the DEWESoft data processing system used in this test. Vibration measurements were carried out for 12 passages of the SML at sites 1 to 3. For the sites 4, 5, 6 and 7, with two operation speeds, the measurements were performed for 6 passages of the SML for each speed. 4. Measurement results and analysis In this section, the measurement results of bridge pier and ground accelerations induced by the HSMT running over the elevated guideway with speeds varying from 150 to 430 km/h were analyzed. The effects of Maglev train speed on vibrations of bridge pier and ground were studied in terms of their peak accelerations at a given test section. Attenuation of ground vibration was investigated by arranging measurement up to 30 m from the track centerline. The effects of guideway configuration

Fig. 8. Time-histories and frequency-spectra of acceleration responses of the pier P0499 with Maglev train speed of 300 km/h: (a) vertical, (b) transverse, and (c) longitudinal.

were also investigated by analyzing the measurement data when the Maglev train ran at a speed of 300 km/h through two different sections.

4.1. Effect of Maglev train speed on bridge pier vibration 4.1.1. Time-domain characteristics of bridge pier vibration Bridge pier vibrations induced by the Maglev train at speeds of 300 km/h and 430 km/h were recorded at Pier P0499 (Site 6) in three directions, as shown in Fig. 8 and Fig. 9, respectively. The line at the section P0499 is a straight route. The train-induced acceleration responses of the pier were recorded for 1.5 s for the 430 km/h train and for 2 s for the 300 km/h train. The acceleration response of the bridge pier is observed to increase with the increase of the Maglev train speed. The peak acceleration responses of the pier were extracted from Fig. 8 and Fig. 9, and the results are plotted in Fig.10. The peak acceleration of the pier in the transverse direction is quite high, reaching

Fig. 7. The test measurements and dynamic signal collecting system. (a) laser velocimeter; (b) and (c) the fixation of sensors on the ground; (d) the fixation of sensors on the pier; (e) dynamic signal collecting devices; (f) dynamic signal collecting system (DEWESoft System).

Fig. 9. Time-histories and frequency-spectra of acceleration responses of the pier P0499 with Maglev train speed of 430 km/h: (a) vertical, (b) transverse, and (c) longitudinal.


6


Fig. 10. Comparison of peak acceleration responses of the pier P0499 for a straight route in three directions with the train speed of 300 and 430 km/h.

2.781 m/s2 when the Maglev train speed is 430 km/h. The vertical and transverse vibrations are increased by 0.96 m/s2 and 1.73 m/s2, respectively, as the Maglev train speed increases from 300 to 430 km/h. In the longitudinal direction, a slight increase of 0.18 m/s2 is recorded. The results show that vertical and transverse vibrations of the pier have a strong correlation with the Maglev train speed, whereas the effect on the longitudinal vibration is moderate.

4.1.2. Frequency-domain characteristics of bridge pier vibration Through the comparison of frequency spectra shown in Fig. 8 and Fig. 9, it can be observed that significant frequencies of pier vibration in three directions increase with the increase of train speed. The dominant frequency of 324 Hz in Fig. 8 and 464 Hz in Fig. 9 respectively, matches well with the maximum characteristic frequency (f1 = v/L1) of 323 Hz and 463 Hz, caused by the center distance of adjacent ferrite cores L1 of the Maglev train at the speed of 300 and 430 km/h respectively. Besides, the values of other significant frequencies are found to be closed to integer multiples of characteristic frequencies f2 and f3, which corresponds to excitation from the suspension magnet and the bogie passage respectively. For example, 376 Hz in Fig. 8 and 425 Hz in Fig. 9 are the 14 and 11 times of the characteristic frequency f2,

Fig. 11. Time-histories and frequency-spectra of acceleration responses of ground at 0 m to the pier P0499: (a) vertical, (b) transverse, and (c) longitudinal with Maglev train speed of 430 km/h.

Fig. 12. Time-histories and frequency-spectra of acceleration response of ground at 2.5 m to the pier P0499: (a) vertical, (b) transverse, and (c) longitudinal with Maglev train speed of 430 km/h.

26.92 Hz and 38.58 Hz, of the Maglev train at the speed of 300 and 430 km/h respectively.

4.2. Effect of Maglev train speed on ground vibration 4.2.1. Time-domain characteristics of ground vibrations Figs. 11–15 show the time histories and frequency spectra of acceleration responses at grounds with different distances to the pier P0499 at the train speed of 430 km/h. The train-induced acceleration responses

Fig. 13. Time-histories and frequency-spectra of acceleration response of ground at 10 m to the pier P0499: (a) vertical, (b) transverse, and (c) longitudinal with Maglev train speed of 430 km/h.



7

Fig. 16. Attenuation of peak ground accelerations with different distances from the pier P0499 in three directions (Maglev train speed of 300 and 430 km/h).


of the ground vibration at the pier were recorded for 1.5 s. The traininduced ground acceleration responses in 3 directions are observed to decrease with the increase of distance to the pier. Fig. 16 shows the effects of train speed and distance from train line on the peak ground accelerations in the three directions when the train passed through the test section near the pier P0499 at speeds of 300 and 430 km/h. It can be seen that the ground accelerations generally attenuate as the distance from the centerline increases. The Maglev

train speed has a significant effect on the vertical ground vibration. A considerable increase of acceleration from 0.375 to 0.659 m/s2 (increase by 0.76 times) and from 0.056 to 0.154 m/s2 (increase by 1.8 times) is observed at the measuring points of 0 and 15 m, respectively, when the train speed increases from 300 to 430 km/h. In contrast, the effects of train speed on the horizontal vibration are lower, and an increase of 0.11 and 0.055 m/s2 (increase by 0.33 times and 0.78 times respectively) for transverse vibration and an increase of 0.1 and 0.045 m/s2 (increase by 0.4 times and 0.52 times respectively) for longitudinal vibration are observed at the measuring points of 0 and 15 m, respectively. Nevertheless, when the vibration energy propagates to the measuring point at 30 m, the peak ground accelerations in three directions attenuate to a quite low level with a slight variation of less than 0.006 m/s2 induced by the train speed varying from 300 to 430 km/h. Through the comparison of the ground vibration in three directions at speed of 300 and 430 km/h in the same section, Maglev train speed is found to have a significant effect on vertical ground vibration but its effect on horizontal ground vibration is lower. 4.2.2. Frequency-domain characteristics of ground vibrations From the frequency spectra of ground vibration accelerations in Figs. 11–13, it can be observed that the dominant frequencies range between 70 to 200 Hz, which are the integer multiples of the characteristic frequency f2 and f3 but are lower than the dominant frequencies of pier vibrations. For example, 77 Hz and 115 Hz are twice and triple of the characteristic frequency f2 (38.58 Hz), also 4 and 6 times of the characteristic frequency f3 (19.29 Hz). Nevertheless, when the vibration energy propagates to the ground beyond 10 m away from the pier, as shown in Figs. 14 and 15, a low frequency of 9.75 Hz, exactly the twice of the carbody gravity-induced characteristic frequency f4 (4.88 Hz), evolves as the predominating constituent of peak acceleration. Besides, the low frequency components induced by characteristic frequency f4 determines the shape of time histories of vibration accelerations, such as a sine wave curve occurs in both Figs. 14 and 15. The reason is that higher frequency vibration decays quicker. Through the frequency-domain analysis, dominant frequencies of ground vibration are highly correlated with characteristic frequencies and lower characteristic frequency becomes predominating over further distance. 4.3. Variations of peak vertical ground acceleration with Maglev train speed


Fig. 17 presents the variation of peak vertical ground accelerations with Maglev train speed varying from 150 to 430 km/h. It can be observed that with the increase of Maglev train speed, all the peak values


8


Fig. 17. Relations of Peak vertical Ground accelerations (PVGA) with Maglev train speed at different distances from the pier. (a) 0 m, (b) 2.5 m, (c) 10 m, (d) 15 m, (e) 20 m, (f) 30 m. The ‘○’ represents the measurement data obtained from the 6 passages passing over the pier. The red lines (——) are the fitted results based on the measurement data. In these linear fitting formulations, v denotes maglev train speed (km/h). VGA is the peak values of vertical ground acceleration (m/s2).

in time-domain exhibit different linearly upward tendencies at different distances from the pier. The variation tendencies of the peak vertical ground accelerations with Maglev train speed are linearly fitted based on the measurement data. From these linear fitting formulations, it can be found that the farther the measuring point from the pier is, the smaller the monomial coefficient is. For example, the monomial coefficient of the fitting formulation at measuring point of 2.5 m to the pier is 0.0011, however, that will decrease to 4.4 × 10− 5 at 30 m to the pier. The variation law of the monomial coefficient indicates that with the increasing distance from pier, the increment of time-domain peak vertical ground acceleration dwindles steadily with the increase of Maglev train speed. For example, as the Maglev train speed rises from 300 to 430 km/h, the peak vertical ground accelerations at measuring point of 2.5 m to pier P0498 increase by 0.199 m/s2, whereas it merely increases by 0.021 m/s2 at the measuring point of 20 m to pier. From the observation, Maglev train speed has a significant effect on the peak vertical ground acceleration but the effect decreases with the increase of the distance to the pier. 4.4. Variation of frequency-weighted ground acceleration with distance from the pier To further investigate the effect of ground vibration induced by HSMT on human body comfort for people on the ground, a frequencyweighted method recommended by ISO2631-1-1997 and Chinese

Standard of Environment Vibration in Urban Area is adopted in this section. The definition of frequency-weighted acceleration level is given by VL ¼ 20 lg

aw af

ð2Þ

where VL (dB) is the frequency-weighted acceleration level; af is 10−6 m/s2 as reference acceleration; aw is the weighted RMS acceleration, calculated as 2 1 aw ¼ 4 T

ZT

312 a ðt Þ5 2

ð3Þ

0

where a(t) is the measurement vibration acceleration (m/s2); and T is the duration of the measurement, in seconds. Fig. 18 shows the relationships between the frequency-weighted acceleration levels in three directions and distance from the pier covering speeds of 150 to 430 km/h, together with corresponding polynomial fitting curves for presentation of the variation tendency. Through comparison of vibration acceleration levels in three directions, it can be found that when Maglev train operates at low speeds, such as 150, 215 and 245 km/h, at sites 1, 2 and 3, the frequency-weighted ground vibration acceleration level in longitudinal direction of the measuring point near the pier is the biggest, compared with the vertical and transverse ground vibration levels. For example, frequency-weighted ground



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Fig. 18. Variations of frequency-weighted ground vibration acceleration level in 3 directions with distance from pier with Maglev train speed of (a) 150 km/h, (b) 215 km/h, (c) 245 km/h, (d) 300 km/h, (e) 350 km/h and (f) 430 km/h, respectively. The polynomial fitting curves and the fitting formulations are also presented. The ‘○’, ‘*’, ‘□’ denote measurement data of vertical, transverse and longitudinal vibration acceleration levels respectively, obtained from the 6 passages passing over the pier. Line ‘——’, ‘ ’ and ‘ ’ represent the fitting curves of vertical, transverse and longitudinal vibration acceleration levels.

vibration acceleration level in longitudinal direction of measuring point at 0 m to pier with speed of 150 km/h is 105 dB, however, those in transverse and longitudinal direction are 99 dB and 96.5 dB respectively. This is probably caused by the acceleration of the Maglev trains when they start running. Nevertheless, the vibration acceleration level in vertical direction becomes predominant, when the vibration energy propagates to the measuring points beyond 20 m away from the pier. It can also be found that when the Maglev train operates at the speed of 300, 350 and 430 km/h at sites 5, 6 and 7, amplifications of the ground vibration were observed in three directions at the area around the location of 15 m away from the bridge pier. For example, when Maglev train operates at the speed of 300 km/h, the vibration level of vertical, transverse and longitudinal vibrations of the ground measuring point at 15 m to the pier are 86.2, 87.2 and 89.3 dB respectively, which are larger than those of the ground measuring point at 10 m to the pier, 81.8, 80.7 and 84.7 dB respectively (Fig. 18d).

It can be concluded that frequency-weighted acceleration level decreases fast with the distance from the pier but the decreasing speed becomes smaller over further distance. 4.5. Effect of guideway configuration on vibrations of bridge pier and ground Fig. 19 presents the acceleration responses of the pier P0298 at a curved route of the line when the train speed is 300 km/h. The girder track is anchored on the pier P0298 with 9-degree inclination and bent with a curvature radius of 4000 m. Fig. 20 shows the comparison of peak acceleration responses between the pier P0499 and the pier P0298 when the SMT ran on the straight route (P0499) and the curved route (P0298) with the same speed of 300 km/h. The results show that the guideway configuration in terms of the track inclination and bend has a significant effect on the transverse vibration of the pier with the response difference of 0.9 m/s2. However, the effect of guideway


10


Fig. 21. Comparison of 3 directional ground peak accelerations with different distances from the pier P0499 in the straight route and the pier P0298 in the curved route (same train speed of 300 km/h).

Based on the above analysis, one conclusion can be drawn that guideway configurations have a considerable effect on transverse ground vibration, nevertheless the effects on vertical and longitudinal ground vibrations are weak.

Fig. 19. Time-histories of acceleration response of the pier P0298: (a) vertical, (b) transverse, and (c) longitudinal. (Maglev train speed of 300 km/h).

configuration on vertical and longitudinal vibrations of the pier is weak. This phenomenon is mainly caused by the centrifugal effect in transverse direction when Maglev train runs on the curved route. This indicates that the dynamic interaction of the Maglev train running on a curved route are different from that running on a straight route. Fig. 21 shows the effect of guideway configuration on peak ground accelerations in three directions and different distances from the centerline of the SML. The vibrations were measured when Maglev train passed through the test sections near the pier P0499 and the pier P0298 with same speed of 300 km/h. It can be seen that the guideway configuration in terms of track inclination and warpage has a significant effect on transverse ground vibration by a significant increase from 0.294 to 0.432 m/s2 at the measuring point of 0 m when the train passed through the curved route compared with the straight route. However, such an increase significantly attenuates with distance. For example, only a small increase of 0.006 m/s2 from straight route to curved route is observed when the distance increases to 15 m. Furthermore, the effect of guideway configuration on vertical and longitudinal ground vibrations is weak.

Fig. 20. Comparison of peak acceleration responses of the pier P0499 in the straight route and the pier P0298 in the curved route (same train speed of 300 km/h).

5. Comparison of vertical ground vibrations induced by HSMT and HSRT To compare with the traditional High Speed Railway Train (HSRT) induced ground vibration, in-situ measurements of wheel railway system with the operation speed of 300 km/h were carried out with the same testing devices in Bengbu in the Anhui Province. The soil conditions are similar with that of SML. The soil condition in the test section is also composed of unconsolidated quaternary sediments with soft grass covered, shown in Fig. 22. The site condition belongs to Site Classification II according to GB50011-2010. Besides, the guideway with double-column piers serves the operation of HSRT. The train is of 16car formation, composed of 8 driving cars and 8 passenger cars. During this experiment, seven measuring points on the ground were selected and consistent with the arrangement of those in HSMT test. The time histories of vertical ground accelerations with train speed of 300 km/h were recorded. Similarly, characteristic frequencies f1, f2, f3 and f4 of ground vibration generated by HSRT train are related with HSRT system's characteristic lengths: the wheelbase (l1), the center distance of adjacent bogies

Fig. 22. Test site of HSRT in Bengbu.



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Fig. 23. Schematic diagram of characteristic lengths of test train.

Table 5 The specific characteristic lengths and frequencies of the test train at speed of 300 km/h. Train type

L1 (m)

L2 (m)

L3 (m)

L4 (m)

CRH380BL Characteristic frequency

2.5 f1 (Hz) 33.3

7.5 f2 (Hz) 11.11

17.4 f3 (Hz) 4.76

24.8 f4 (Hz) 3.36

Fig. 25. Time-histories and frequency-spectra of vertical ground vibration accelerations induced by HSRT at measuring point of (a) 0 m, (b) 2.5 m, (c) 10 m, (d) 20 m and (e) 30 m, with train speed of 300 km/h.

Fig. 24. Time-histories and frequency-spectra of vertical ground vibration accelerations induced by HSMT at measuring point of (a) 0 m, (b) 2.5 m, (c) 10 m, (d) 20 m and (e) 30 m, with train speed of 300 km/h.

between the forward car and the backward (l2), the length between two bogie centers in one car (l3), and the center distance of two neighboring cars, shown in Fig. 23. From the characteristic analysis of HSRT (Zhai et al., 2015), the dominant frequencies with maximum amplitudes are related with the fundamental carriage length frequency f4. Meantime, f1, f2 and f3 provide a modulate amplitude effect. Table 5 lists the specific characteristic lengths and frequencies of the test train at speed of 300 km/h. Figs. 24 and 25 show the comparison of vertical ground vibration acceleration responses of HSMT and HSRT in both time and frequency-domain at the same speed of 300 km/h. It can be deduced that different systems result in the different vertical ground accelerations even with the same speed and same distance from the pier. Overall, the peak values of vertical acceleration induced by HSMT are nearly 50% higher than that induced by HSRT with same distance, shown in Fig. 26. It can also be found that these two are of the similar attenuation trend, meanwhile, the ground vibration amplifications were both observed around the location of 15 m away from the bridge pier. Besides, the values of dominant frequency components of HSMT are generally higher than those of HSRT, detailedly shown in Fig. 27 and Fig. 28, which present the frequency spectra of vertical ground vibration acceleration of the measuring points at 2.5 m and 20 m to


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highest frequency (40.6 Hz) is equal to 12f4. However, when vibration energy propagates to the measuring point at 20 m to pier, the value of main frequency decreases, 26.8 Hz and 10 Hz for HSMT and HSRT respectively, both of which are lower than those at 2.5 m to the pier. The values of dominant frequencies induced by HSRT at speed of 300 km/h are all integer times of characteristic frequency f4, shown in Fig. 28(b). But for HSMT, the characteristic frequency f4 becomes one of the dominant frequencies, such as 3.4 Hz and 6.8 Hz, shown in Fig. 27(b), which are not found in Fig. 27(a). The other dominant frequencies are all integer multiples of characteristic frequency f2 and f3, similar with the statics in Fig. 27(a).

6. Discussion and conclusion Fig. 26. Comparison of peak values of vertical ground vibration accelerations induced by HSMT and HSRT at speed of 300 km/h.

pier with speed of 300 km/h, respectively. Through comparison of statics in the Fig. 27(a) and Fig. 28(a), it can be seen that the main frequency of HSMT (135 Hz) is larger than that of HSRT (33.6 Hz). The former is due to characteristic frequency f2 and f3, detailed in Table 3. The latter is due to characteristic frequency f1 and f4, detailed in Table 5. The values of dominant frequencies in Fig. 27(a) are integer multiples of the characteristic frequency f2 and f3. For example, the second highest frequency (81 Hz) is triple of f2 , and also 6 times of f 3. Identically, in Fig. 28(a), the second

Field measurements of bridge pier and nearby ground vibrations induced by Maglev trains were performed on the Shanghai Maglev Line (SML) in China. During the measurements, the Maglev trains ran on the elevated guideway with different speeds varying from 150 km/h to 430 km/h. By analyzing the measurement data, the effects of Maglev train speed on the bridge pier and nearby ground vibrations were investigated in terms of peak acceleration at a given test section. The effects of guideway configuration on the bridge pier and nearby ground vibrations were investigated in terms of peak acceleration when the train passed through the two test sections with same speed of 300 km/h. Besides, a comparison analysis of vertical ground vibration accelerations induced by HSMT and

Fig. 27. Frequency spectra of vertical ground vibration acceleration at the measuring points of (a) 2.5 m and (b) 20 m to pier induced by HSMT with speed of 300 km/h. The symbol ‘○’ denotes the dominant frequency.

Fig. 28. Frequency spectra of vertical ground vibration acceleration at the measuring points of (a) 2.5 m and (b) 20 m to pier induced by HSRT with speed of 300 km/h. The symbol ‘○’ denotes the dominant frequency.



HSRT are performed at the same speed of 300 km/h. Some conclusions can be drawn as follows: (1) Vertical and transverse vibrations of the bridge pier have a strong correlation with Maglev train speed, whereas the effect of train speed on longitudinal vibration is moderate. (2) Guideway configurations in terms of track inclination and warpage have a significant effect on transverse vibration of the bridge pier but the effects on vertical and longitudinal vibrations are weak. (3) Maglev train speed has a significant effect on vertical ground vibration but its effect on horizontal ground vibration is lower. (4) Guideway configurations in terms of track inclination and warpage have a considerable effect on transverse ground vibration. By contrast, their effects on vertical and longitudinal ground vibration are weak. (5) When the Maglev train operates at the speed of 300, 350 and 430 km/h, an amplification of ground vibration occurs around the location of 15 m away from the pier in three directions. (6) When the Maglev train passes at the corner of SML with a high speed or high acceleration, the ground peak accelerations in transverse and longitudinal directions increase to the same level as the vertical peak ground vibration. Therefore, the horizontal ground vibration should also be considered. (7) Compared to the vertical ground vibration induced by HSRT with same speed of 300 km/h, the peak accelerations induced by HSMT are nearly 50% larger than those of HSRT.

Acknowledgement This work is financially supported by the National Key Technology R&D Program of 12th Five-Year Plan of China (Project No: 2013BAG19B00-02-03). The joint PhD scholarship provided by The Hong Kong Polytechnic University to the first author is also appreciated. This measurement was performed with the help of Shanghai Maglev Transportation Development Co., Ltd. and the students from Tongji University. References Auersch, L., 2006. Ground vibration due to railway traffic — the calculation of the effects of moving static loads and their experimental verification. J. Sound Vib. 293 (3–5), 599–610. Bi, S., 2015. Vibration characteristic analysis of elevated Maglev transportation. In ICTE 2015, 2190–2195.

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