Mohamed Abdel-Ghaffar Symposium at USC September 19, 2008
Modal Analysis of Bridge Structures: An Application to Noise Generation from Modular Expans...
Mohamed Abdel-Ghaffar Symposium at USC September 19, 2008
Modal Analysis of Bridge Structures: An Application to Noise Generation from Modular Expansion Joint
Hiroki Yamaguchi Saitama University
1
MEMORY OF PROF. ABDEL-GHAFFAR
International Seminar on CableSupported Bridges, Yokohama, Japan, December 10,1991. 2
Impact of Prof. Abdel‐Ghaffar’s Work http://stevens.usc.edu/read_article.php?news_id=282
Ahmed M. Abdel-Ghaffar, an internationally known USC civil engineering professor specializing in the analysis and monitoring long span flexible bridges, died April 17 after a long illness. Abdel-Ghaffar’s 1974 investigation of the dynamic characteristics of the Vincent Thomas Bridge in Los Angeles, done when he was a graduate student, led to new standards on how to collect, analyze and interpret structural dynamic measurements from complex, three-dimensional, extended structures. Experimental and Theoretical Modal Analysis of Bridge Structures: An Application to Noise Generation from Modular Expansion Joint 3
BACKGROUND Modular Expansion Joint
Middle Beam Rubber Sealing
Large expansion capacity in both translation and rotation Drainage of water and debris with the use of rubber sealing DRAWBACK: Louder noise is generated and radiated when the vehicle crosses the joint and this has been a localized environmental problem. 4
OBJECTIVES Input-Output System Diagram of Joint Noise Problem
Car Running
Joint Structure Cavity
Structure Vibration
Bridge Structure Cavity
Air Vibration
Transfer Characteristics Natural freq. & mode of joint structure Acoustic freq. & mode of sealing gap
Air
Transfer Characteristics Mass Additio n Gap Filling
Sound Receiving Point
Human
Response
Noise
Transfer Characteristics
Annoyance ・Frequency Domain ・Time Domain
Sound Barrier
Noise Control
Mechanism of noise generation from modular joint in highway bridges 5
Car-Running Experiment with Full-Scale Model of Modular Joint
6
FULL-SCALE MODEL OF JOINT
Sedan-Type Two-Axle Car Car Speed: 50 km/h
Sound Level Meter 7
TIME SERIES OF SOUND & VIBRATION
Sound below the joint
Sound above the joint
Lateral acceleration The Fourier spectrum was obtained by scanning a Hanning window of length 0.4096sec over the first 0.6sec record.
Vertical acceleration 8
SPECTRA OF SOUND PRESSURE
Car running over the control beams
Car running over the support beams
Above the joint
Below the joint
9
MECHANISM OF NOISE ABOVE JOINT
Acoustic characteristics of gap
10
MECHANISM OF NOISE BELOW JOINT Acoustic characteristics of test cavity
Dynamic characteristics of joint
11
DYNAMIC CHARACTERISTICS OF JOINT
Impact testing
FEM analysis 12
NATURAL FREQ. & MODE SHAPE
Lateral vibration mode
Vertical vibration mode 13
VIBRO-ACOUSTIC ANALYSIS BY FEM 1. Dominant contribution from structural mode
f = 161 Hz
f = 160 Hz
f = 162 Hz
2. Significant contribution from structural and acoustic modes f = 267 Hz
f = 268 Hz (a)
(b)
f = 269 Hz (c)
14
POSSIBLE SOURCES OF NOISE GENERATION
Rubber sealing
Gap
Deck
Deck Support beam cavity Girder
Girder Structural-acoustic interaction
Pier 15
Field Measurement of Noise Generated from Modular Expansion Joint in Highway Bridges
16
FIELD MEASUREMENT: STEEL BRIDGE Expansion joint Concrete deck slab
Cavity below the joint Cavity below the joint
Steel I-girder
Expansion joint
THE HACCHOME BRIDGE Bridge length of 184.6m with 5 continuous spans Non-composite, four steel I-girder with concrete deck slab Modular joint for the new bridge Finger joint for the old bridge with five I-girder 17
POSITION OF NOISE METERS Above the bridge Expansion joint
6m
Bridge abutment
5m
Bridge side
Just below the joint 5m
Under the girder 18
POSITION OF ACCELEROMETERS
Middle beam of joint
Concrete deck slab
Web plate of I-girder
ÉW ÉC Éá Éìïž Ég ñ ê} ÉW
ÉC á
Ég ì
ï ž ñ
ê}
19
TIME SERIES OF VIBRATIONS & SOUND
Joint Vibration
Girder’s Web Vibration
Slab Vibration
Sound under Girder 20
Vibration of Girder Web
Frequency (Hz)
Vibration of Joint
Frequency (Hz)
Sound under Bridge
Sound Pressure Frequency (Hz) (Pa)
TIME-FREQ. PLOT OF SOUND UNDER BRIDGE
(WTC)
Time (s)
Time (s)
3621
Sound Pressure (Pa)
TIME-FREQ. PLOT OF SOUND ABOVE BRIDGE
Frequency (Hz)
(WTC)
Acceleration
(m/s2)
Time (s)
Time (s)
Joint Vibration 22
FIELD MEASUREMENT: CONCRETE BRIDGE Expansion joint
Concrete box-girder
Cavity below the joint
Expansion joint
THE UTSUKUSHIMA BRIDGE Bridge length of 208m with 3 continuous spans PC box-girder Modular joint with five middle beams 23
POSITION OF NOISE METERS
Just below the joint
Bridge side
Under the girder
Above the bridge Cavity below the joint
2.62m
Just below the joint Bridge Pier
Under the girder
7m 5m
10m Bridge side 24
POSITION OF ACCELEROMETERS
Support beam of joint
Upper slab of box-girder
20m Box-girder
Approach
Middle beam of joint
7.35m
5m
Expansion joint
25
TIME SERIES OF VIBRATION & SOUND
Joint Vibration
Sound below Joint
Sound under Girder
Sound above Bridge
Sound beside Bridge 5m
Sound beside Bridge 15m 26
5
5
Joint Vibration
2
Joint Vibration
Acceleration â¡ë¨ìx[m/s (m/s ] 2)
2 Acceleration â¡ë¨ìx[m/s ](m/s2)
TIME-FREQ. PLOT OF SOUND IN PC BRIDGE
0
0
-5
-5 0
0.1
0.2
0.3 éû ä‘ [s ]
0.4
0.5
0.6
0
0.1
0.2
Sound below Joint
900
900
800
800
700
700
600 500 400 300 200
0.5
0.6
600 500 400 300 200 100
100 0
0.4
Sound above Bridge
1000
Acceleration (m/s2)
Acceleration (m/s2)
1000
0.3 éû ä‘ [s ] Time (s)
Time (s)
0.1
0.2
0.3
Time (s)
0.4
0.5
0.6
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (s)
(3) 700-800Hz: non-stationary component (2) 400-600Hz due to Joint Cavity Sound due to Sealing Gap Sound (1) 100-200Hz: main, stationary component due to Joint Vibration 27
CONCLUDING REMARKS The noise generated above the joint is dominated by frequency components in the frequency range from 500 to 800 Hz, which is attributed to a sudden change in the air pressure within the gap formed by the rubber sealing with the two adjacent middle beams when a car runs over the gap. The noise generated below the joint is mainly dominated by the frequency components in the frequency range below 200 Hz, which is caused by the sound radiation due to the bending vibration modes of the middle beams being excited by an impact force from the car wheels. The noise generated below the joint can be significantly affected by the acoustic characteristics of the cavity below the joint in the sense that there is a possibility of acoustic resonance in the space. The sound radiation efficiency of the joint-cavity system appeared to be high at natural frequencies of vibration modes of the joint with significant vertical vibration of middle and support beams.
28
OUTLINE Modal Analysis of Bridge Structures: An Application to Noise Generation from Modular Expansion Joint
• Background • Objectives • Car-Running Experiment with Full-Scale Model of Modular Expansion Joint – Experimental Modal Analysis of Model Joint and Cavity – Theoretical Modal Analysis of Model Joint and Cavity
• Field Measurement of Noise Generated from Modular Expansion Joint in Highway Bridges • Concluding Remarks 29
NOISE UNDER THE BRIDGE Finger Joint Sound pressure (Pa)
Sound pressure (Pa)
Modular Joint
Sound pressure (Pa)
Frequency (Hz)
Frequency (Hz)
Truck
Frequency (Hz)
Dominant in low freq. region
モジュラー型ジョイント通 過によるジョイント音の影 響 30
NOISE ABOVE THE BRIDGE Finger Joint Sound pressure (Pa)