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Noise emission from trams
Journal ofSound
and Vibrarion (1988) 120(2), 281-286
NOISE
EMISSION Y.
FROM
TRAMS
K. WIJNIA
Van Dormer b.v., 2e SweeZinckstraat 148, 2517 HB The Hague, The Netherlands (Received 15 November 1986)
The noise emission from trams on various tracks has been determined in Rotterdam. The noise level along the track is influenced by the mechanical impedance of rail and wheel, and by the reflection of the sound wave on the surface. The manner in which the noise level is affected by the various track surfaces and the different types of tracks has been studied and the results are shown in this report. The noise produced by the tram wheels on the different tracks varies 6 dB(A) due to the mechanical impedance of the track only. In this study one type of wheel was used; however, the noise level may change if another type of wheel is used. 1. INTRODUCTION When a track of the Rotterdam tramway needed to be replaced, the question arose which type of track construction should be used. The following criteria were taken into consideration: the track must have low maintenance costs; replacing the wheels should be simple; the rails must form part of the pavement; the rails must not cause squealing noise in the curves; the rails must have a low noise production. For the past 20 years, 11 different types of tramtracks have been used in Rotterdam. The amount of noise caused by a tram travelling at 40 km/h along the tracks has been measured. A microphone was placed at 7.5 m from the centreline of the track, at l-3 m + above ground. Only the ZGT 4/6 tram type, without wheelflats, was measured (ZGT 4/6 is shown in Figure 1).
Figure 1. Tram ZGT 4/6; total weight 246 kN; wheels Bochum type (rubber springs).
281 0022-460X/88/020281
+06 $03.00/O
@ 1988 Academic
Press Limited
282
Y. K. WIJNIA
The rails on each track should have the same condition; therefore they were all ground before measurements took place. 2. TYPES OF TRAMTRACKS The 11 types of tramtracks (groups a, b and c) as shown in Figures 2-5 are listed in Table 1.
Figure 2. Example of track type a: rail in sand.
Figure 3. Example of track type b; rail on concrete sleeper.
Figure 4. Example of track type b: rail on concrete sleeper (in soil).
NOISE
EMISSION
FROM
283
TRAMS
Figure 5. Example of track type c: rail on reinforced concrete.
TABLE
1
Types of tramtracks Track
ALpt (WA))
type 1. Rail NP 4-4A 2. Rail NP 4-4A 3. Rail NP 4-4A 4. Rail NP 4-4A
5. 6. 7. 8. 9.
10. 11.
in bricks (100 x 100 x 200 mm) in bricks (55 x 105 x 210 mm)
on steel sleepers c+c 4.00 m in gravel on concrete slab in asphalt street; between rail and concrete slab, a mixture of sand and polyester (total reflecting surface) Rail R 41 on concrete sleepers in gravel Rail NP 4-4A on concrete slab in asphalt pavement; between railside and concrete slab are bricks Rail NP 4 on concrete sleepers in sand covered with soil to the top of the rail; grass is growing on the soil As 7, however, gravel instead of sand beneath the sleepers Rail NP4-4A on concrete sleepers in asphalt pavement (approx. 30 mm thick); the area between rail and concrete sleepers is filled with concrete Nikex construction (Budapest) rail, 70 mm high, on a reinforced concrete slab Rail R 41 clamped directly onto a reinforced concrete flyover
+0*5
a a b”
-2-o +l-8 Reference
b b
-2.4 -0.6
b
-4.0
b C
-1.7 -0.2
C
+0*5
C
-4.3
t ALP is the difference in sound pressure level caused by the reflection of the surface (all frequency spectra
are adjusted to the surroundings of track number 4).
3. METHOD
USED TO ELIMINATE THE DIFFERENCE SOUND WAVE REFLECTION
For the 11 different types of tramtracks, from the centreline at a height of l-3 m+ were carried out to establish the influence
IN
measurements were to be carried out at 7.5 m above ground. Supplementary measurements of the sound wave reflection.
284
Y. K. WIJNIA
-,,-
31.5
63
125
250
500
Frequency
‘[\
IO00
2000
4000
8000
klz)
7500 (mm)
f$J
Figure6. Theoretical difference between sound pressure level in a free field and a total reflecting surface situation. (a) microphone at 6.8 m distance, 1.3 m + above ground; (b) - - -, microphone as (a) but source at 0.5 m+ abbve ground.
A loudspeaker with a flat frequency response of 100-10 000 Hz was installed and fed with white noise. The centre of the loudspeaker was placed at two positions, at 0.1 m and 0.5 m respectively, above the rail nearest to the microphone. The amplifier output was the same at each measurement. The microphone was placed in the same position as the one used during the sound level measurements of the tram. Figure 6 shows the theoretical difference between the sound pressure levels in a free field and those for a total reflecting surface situation. The difference in sound pressure levels between the free field and track number 4 (asphalt pavement) as actually measured does not correspond with Figure 6 (cf. Figure 7). For a reliable comparison of the sound levels, all measurements were therefore to be adjusted to the surface of the reference track (track number 4).
31.5
63
125
250
500
Frequency
1000
2000
4000
EC00
(Hz)
Figure7. Actually measured difference between a free field and the ground of track 4; (a) as Figure 6.
and (b) - - -
EMISSION
NOISE
4. RESULTS
FROM
AND
285
TRAMS
DISCUSSION
The frequency spectrum of the passing tram is shown in Figure 8. The maximum in the A-weighted spectrum was situated between 500 and 1000 Hz. The adjusted dB(A) results are shown in Figure 9. The radiation of sound from the rail, even at tracks 5 and 11, was negligible compared to the sound radiation from the wheels.
31.5
63
125 f
Figure 8. A-weighted sound pressure 2; - - -, measurement 3.
/
2
250
Octave
500
bond centre
1000
level for three tram passages.
3
4
5
6
2000
frequency
7
-,
8
4000
8000
ktz)
Measurement
9
IO
1; ----, measurement
II
Track
Figure 9. Adjusted maximum sound level measured at a distance of 7.5 m, with a tram going along each of the 11 tracks at 40 km/h. The difference due to the reflected sound wave, as given in section 3, has been subtracted from the measured sound level.
286
Y. K. WIJNIA TABLE 2
Indication
of the sound emission for the various track types: increase in sound level in dB(A) Track
Acoustic Acoustic Acoustic
soft hard
environment
Group a
Group b
Group c
0t 3
3 6
6 9
t Under the most favorable circumstances, which consist of a track from group a combined with an acoustic soft environment, the sound level (L,,,) measured at a distance of 7.5 m and at a speed of 40 km/h is 80 + 2 dB( A).
In Table 2 the effect of the track types as well as the effect of the surface is given in steps of 3 dB(A). It can be concluded that the noise radiation may vary 6 dB(A) due to the effect of the mechanical impedance of the rail only.
and Vibrarion (1988) 120(2), 281-286
NOISE
EMISSION Y.
FROM
TRAMS
K. WIJNIA
Van Dormer b.v., 2e SweeZinckstraat 148, 2517 HB The Hague, The Netherlands (Received 15 November 1986)
The noise emission from trams on various tracks has been determined in Rotterdam. The noise level along the track is influenced by the mechanical impedance of rail and wheel, and by the reflection of the sound wave on the surface. The manner in which the noise level is affected by the various track surfaces and the different types of tracks has been studied and the results are shown in this report. The noise produced by the tram wheels on the different tracks varies 6 dB(A) due to the mechanical impedance of the track only. In this study one type of wheel was used; however, the noise level may change if another type of wheel is used. 1. INTRODUCTION When a track of the Rotterdam tramway needed to be replaced, the question arose which type of track construction should be used. The following criteria were taken into consideration: the track must have low maintenance costs; replacing the wheels should be simple; the rails must form part of the pavement; the rails must not cause squealing noise in the curves; the rails must have a low noise production. For the past 20 years, 11 different types of tramtracks have been used in Rotterdam. The amount of noise caused by a tram travelling at 40 km/h along the tracks has been measured. A microphone was placed at 7.5 m from the centreline of the track, at l-3 m + above ground. Only the ZGT 4/6 tram type, without wheelflats, was measured (ZGT 4/6 is shown in Figure 1).
Figure 1. Tram ZGT 4/6; total weight 246 kN; wheels Bochum type (rubber springs).
281 0022-460X/88/020281
+06 $03.00/O
@ 1988 Academic
Press Limited
282
Y. K. WIJNIA
The rails on each track should have the same condition; therefore they were all ground before measurements took place. 2. TYPES OF TRAMTRACKS The 11 types of tramtracks (groups a, b and c) as shown in Figures 2-5 are listed in Table 1.
Figure 2. Example of track type a: rail in sand.
Figure 3. Example of track type b; rail on concrete sleeper.
Figure 4. Example of track type b: rail on concrete sleeper (in soil).
NOISE
EMISSION
FROM
283
TRAMS
Figure 5. Example of track type c: rail on reinforced concrete.
TABLE
1
Types of tramtracks Track
ALpt (WA))
type 1. Rail NP 4-4A 2. Rail NP 4-4A 3. Rail NP 4-4A 4. Rail NP 4-4A
5. 6. 7. 8. 9.
10. 11.
in bricks (100 x 100 x 200 mm) in bricks (55 x 105 x 210 mm)
on steel sleepers c+c 4.00 m in gravel on concrete slab in asphalt street; between rail and concrete slab, a mixture of sand and polyester (total reflecting surface) Rail R 41 on concrete sleepers in gravel Rail NP 4-4A on concrete slab in asphalt pavement; between railside and concrete slab are bricks Rail NP 4 on concrete sleepers in sand covered with soil to the top of the rail; grass is growing on the soil As 7, however, gravel instead of sand beneath the sleepers Rail NP4-4A on concrete sleepers in asphalt pavement (approx. 30 mm thick); the area between rail and concrete sleepers is filled with concrete Nikex construction (Budapest) rail, 70 mm high, on a reinforced concrete slab Rail R 41 clamped directly onto a reinforced concrete flyover
+0*5
a a b”
-2-o +l-8 Reference
b b
-2.4 -0.6
b
-4.0
b C
-1.7 -0.2
C
+0*5
C
-4.3
t ALP is the difference in sound pressure level caused by the reflection of the surface (all frequency spectra
are adjusted to the surroundings of track number 4).
3. METHOD
USED TO ELIMINATE THE DIFFERENCE SOUND WAVE REFLECTION
For the 11 different types of tramtracks, from the centreline at a height of l-3 m+ were carried out to establish the influence
IN
measurements were to be carried out at 7.5 m above ground. Supplementary measurements of the sound wave reflection.
284
Y. K. WIJNIA
-,,-
31.5
63
125
250
500
Frequency
‘[\
IO00
2000
4000
8000
klz)
7500 (mm)
f$J
Figure6. Theoretical difference between sound pressure level in a free field and a total reflecting surface situation. (a) microphone at 6.8 m distance, 1.3 m + above ground; (b) - - -, microphone as (a) but source at 0.5 m+ abbve ground.
A loudspeaker with a flat frequency response of 100-10 000 Hz was installed and fed with white noise. The centre of the loudspeaker was placed at two positions, at 0.1 m and 0.5 m respectively, above the rail nearest to the microphone. The amplifier output was the same at each measurement. The microphone was placed in the same position as the one used during the sound level measurements of the tram. Figure 6 shows the theoretical difference between the sound pressure levels in a free field and those for a total reflecting surface situation. The difference in sound pressure levels between the free field and track number 4 (asphalt pavement) as actually measured does not correspond with Figure 6 (cf. Figure 7). For a reliable comparison of the sound levels, all measurements were therefore to be adjusted to the surface of the reference track (track number 4).
31.5
63
125
250
500
Frequency
1000
2000
4000
EC00
(Hz)
Figure7. Actually measured difference between a free field and the ground of track 4; (a) as Figure 6.
and (b) - - -
EMISSION
NOISE
4. RESULTS
FROM
AND
285
TRAMS
DISCUSSION
The frequency spectrum of the passing tram is shown in Figure 8. The maximum in the A-weighted spectrum was situated between 500 and 1000 Hz. The adjusted dB(A) results are shown in Figure 9. The radiation of sound from the rail, even at tracks 5 and 11, was negligible compared to the sound radiation from the wheels.
31.5
63
125 f
Figure 8. A-weighted sound pressure 2; - - -, measurement 3.
/
2
250
Octave
500
bond centre
1000
level for three tram passages.
3
4
5
6
2000
frequency
7
-,
8
4000
8000
ktz)
Measurement
9
IO
1; ----, measurement
II
Track
Figure 9. Adjusted maximum sound level measured at a distance of 7.5 m, with a tram going along each of the 11 tracks at 40 km/h. The difference due to the reflected sound wave, as given in section 3, has been subtracted from the measured sound level.
286
Y. K. WIJNIA TABLE 2
Indication
of the sound emission for the various track types: increase in sound level in dB(A) Track
Acoustic Acoustic Acoustic
soft hard
environment
Group a
Group b
Group c
0t 3
3 6
6 9
t Under the most favorable circumstances, which consist of a track from group a combined with an acoustic soft environment, the sound level (L,,,) measured at a distance of 7.5 m and at a speed of 40 km/h is 80 + 2 dB( A).
In Table 2 the effect of the track types as well as the effect of the surface is given in steps of 3 dB(A). It can be concluded that the noise radiation may vary 6 dB(A) due to the effect of the mechanical impedance of the rail only.