114 W. Locke et al. Fig. 3 Aerial and side elevation photographs of HLC bridge. Photographs are provided by the authors of [32] configuration, sensors were installed on the axles and as close to the center of each wheel as possible; while for the sprung configuration, sensors were installed directly above unsprung sensor locations on the vehicle body. A total of four uni-axial accelerometers were available for testing on the RAM truck, meaning sprung and unsprung tests were conducted separately. 4 Testing Strategy Experiments for coupled and uncoupled system identification were conducted in this study. Uncoupled system identification experiments were conducted first to identify bridge and vehicle properties prior to DBHM testing. The experiments for uncoupled system identification are listed under items one and two below, while experiments for coupled system identification are listed under item three. 1. Uncoupled Bridge Testing: To detect bridge frequencies under true operating conditions without worrying about time constraints and the safety of personnel on the bridge, traffic tests were conducted two days prior to DBHM testing. During testing, the direct bridge response was recorded with ongoing traffic flowing at the posted speed limit of 72.42 kph (45 mph). A total of 20 records were collected for each bridge configuration, with the length of each record being sixty seconds long. With the exception of down time to switch configurations, each record was taken sequentially to ensure minimal variation in bridge properties caused by changing environmental parameters. It should be noted that at the time of testing, Sensor A in the BDI system was malfunctioning; because of this, only the data collected from Sensors B and C were used to obtain the results in Sect. 6.2. This issue was resolved before DBHM testing.
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