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Frequency (Hz)

SF (south). Sausalito (north). 500 ft. Time plot, vertical sensors at L1-L5. Frequency plot, vertical sensors at L1-L5. 8. V2. 4200 ft. V2. V4. 1125 ft. 246 ft. 6. V13. V4. V7. V13. 4. 56 nodes. 10. 4. V9. V7. V9. 8 nodes. 2. Acceleration (mg). 0. abs(FFT(.)). 2. 10.

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Frequency (Hz)

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  1. SF (south) Sausalito (north) 500 ft Time plot, vertical sensors at L1-L5 Frequency plot, vertical sensors at L1-L5 8 V2 4200 ft V2 V4 1125 ft 246 ft 6 V13 V4 V7 V13 4 56 nodes 10 4 V9 V7 V9 8 nodes 2 Acceleration (mg) 0 abs(FFT(.)) 2 10 -2 -4 0 10 -6 -8 0 1 2 3 4 5 6 7 8 9 10 -2 Time (sec) 10 0 2 4 6 8 10 12 14 16 18 20 Frequency (Hz) Sentri (Application Layer) Straw FTSP BufferedLog Broadcast MintRoute Best-effort Single-hop Communication Low-level FLASH ADXL 202E Silicon Designs 1221L 1.00 0.74 0.19 -0.73 -0.99 quarter-span mid-span 260ft 9 7 5 1 2 11 16ft 12 Berkeley 14 SF Bay 10 8 13 4 3 Base Station Wireless Sensor Networks for Structural Health Monitoring Sukun Kim*, Shamim Pakzad+, David Culler*, James Demmel*, Gregory Fenves+, Steve Glaser+, Martin Turon# * EECS, UC Berkeley +CEE, UC Berkeley #Crossbow Overview Vibration Data from the Footbridge • Ambient vibrations of the structure are monitored and used to determine the health status of the structure. • With a Wireless Sensor Network, low cost monitoring is possible without interfering with the operation of the structure. First Vertical Mode of Vibration Challenges • High Fidelity Data • High Frequency Sampling with Low Jitter • Time Synchronized Sampling [FTSP] • Large-scale Multi-hop Network [Mint] • Reliable Command Dissemination [Broadcast] • Reliable Data Collection [Straw] Accelerometer Board Estimated results match with a FE model of the bridge (SAP) Deployment at the Golden Gate Bridge • Two measurement axis each with two accelerometers • Thermometer, 16bit ADC, Low-pass filter • On-board Digital Signal processing • Calibration for manufacturing variation and temperature • Nodes on the main span and the south tower • Distance between nodes on the west span is either 100ft or 50ft • Exposed to strong and salty wind and fog Software Architecture • When sampling, only necessary components are turned on to reduce jitter • Straw provides reliable data collection • Selective-NACK is used – complexity is drawn from the sender (mote) to the receiver (PC) • Rate-based control • Pipelining increases channel utilization Node, Battery, Antenna Rusting of C-clamp Base station in Tower Deployment at the Footbridge • Vertical, Quarter span • North of the South Tower (b) Vertical, Quarter span South of the North Tower

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