Experimental Evaluation of Drive-by Health Monitoring on a Short-Span Bridge Using OMA Techniques 115 Table 1 Specifications for BDI and B&K data acquisition systems BDI system Accelerometers Frequency Sensitivity Noise level Sample rate Mounting Type: Model range (Hz) (mV/g) (µg/Hz) [fs] (Hz) method MEMS: A1521-002 0–400 1000 5 1000 Loctite 410 DAQ Number of Wireless Input range Max sample Power Model channels (Y/N) (kHz) rate (kS/s) supply STS4-4-IW3 4 Y Not given 1 Li-Ion battery B&Ksystem Accelerometers Frequency Sensitivity Noise level Sample rate Mounting Type: Model range (Hz) (mV/g) (µg/Hz) [fs] (Hz) method Piezo: 4507-B-006 0.2–6000 490±5% 8 1024 Loctite 410 DAQ Number of Wireless Input range Max sample Power Model channels (Y/N) (kHz) rate (kS/s) supply LAN-XI 3050 6 N DC-51.2 131 DC to AC power inverter Fig. 4 Configurations for BDI accelerometers 2. Uncoupled RAM Truck Testing: To distinguish between vehicle and surface roughness frequencies, road tests were conducted at speeds of 32.19 kph (20 mph), 48.28 kph (30 mph), 64.37 kph (40 mph), and 80.47 kph (50 mph). A total of five records were collected at each speed with sensors installed on the unsprung and then sprung mass (i.e. a total of forty tests were performed); the length of each record was sixty seconds. All tests were conducted on freshly paved sections of US-123 between Clemson, SC and Easley, SC. 3. Coupled Vehicle-Bridge (DBHM) Testing: Individual DBHM tests were conducted with only the test vehicle crossing the subject bridge span when it was free of traffic. Testing was conducted concurrently with planned load testing for the SCDOT; therefore, as many tests as possible were performed while the bridge was closed to traffic for this activity. A total of six tests were conducted while vehicle sensors were installed on the unsprung mass and the vehicle was traveling 32.19 kph (20 mph); the length of each record was 30 s. For consistency, the driver and DAQ operator used for RAM road tests were also used for DBHM testing. Direct bridge measurements were also taken during DBHM tests, with the length of each record also being thirty seconds; this data was used to validate the system identification results obtained from the traffic tests conducted days prior. It should be noted that RAM tests were only conducted under Configuration B, meaning Configuration A was not considered during the coupled system analysis. Because the bridge and vehicle DAQ units were not connected, a speed-bump trigger mechanism was employed to help inform both systems when the vehicle was 30.5 m (100 ft) away from the subject bridge span. When the vehicle hit the speed-bump, the vehicle accelerometers recorded the sudden impulse, while a BDI transducer recorded sudden speed-bump displacements and the time of these two events were manually synchronized. It should be noted that excitations from the speed-bump dampened out before the vehicle reached the bridge. Additionally, a person was positioned at the start of exterior span 4 to provide supplemental position data by recording the approximate times the vehicle entered and exited the bridge span.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==