We propose a method for load rating of prestressed box beam (PSBB) bridges based on their dynamic response collected
using wireless sensor networks (WSNs). The hypothesis includes that the health of a bridge is associated with its
vibration signatures. We deployed two WSNs on a 25-year old PSBB bridge, and ran trucks with variable loads and
speeds for collecting its real-time dynamic response at current condition. We also performed FE simulations of 3-D
bridge models under vehicular loads to acquire the representative dynamic response at its newest condition. We validated
the bridge model by field testing and numerical analysis. We used Fast Fourier Transform and peak-picking algorithms
to find maximum peak amplitudes and their corresponding frequencies. We calculated the in-service stiffness of the
bridge to determine its load rating, which resembles the actual load rating of the bridge. The application software
developed from this research can instantly determine the load rating of a PSBB bridge by collecting its real-time
dynamic response. The research outcome will help reduce bridge maintenance costs and increase public safety.
KEYWORDS: Bridges, Sensors, Sensor networks, Fourier transforms, Data modeling, Finite element methods, 3D modeling, Inspection, Software development, Analytical research
We propose dynamic response based condition assessment of prestressed box beam (PSBB) bridges that will be more
realistic and cost-efficient. The hypothesis includes that the dynamic response is a sensitive indicator of the physical
integrity and condition of a structure. We deployed two wireless sensor networks for collecting the real-time dynamic
response of a 25-year old PSBB bridge under trucks with variable loads and speeds. The dynamic response of the bridge
at its newest condition was collected from FE simulations of its 3-D FE models mimicking field conditions. The FE
model was validated using experimental and theoretical methods. We used Fast Fourier Transform and peak-picking
method to determine peak amplitudes and their corresponding fundamental frequencies at its newest and current
condition. The analyses interestingly indicate a 37% reduction in its fundamental frequency over a 25-year service life.
This reduction has been correlated to its current visual inspection to develop application software for quick and efficient
condition assessment of PSBB bridges. The research outcome will provide an efficient and cost-effective solution for
bridge inspection and maintenance.
Health monitoring of rotorcraft components, which is currently being performed by Health and Usage Monitoring Systems (HUMS) through analyzing vibration signatures of dynamic mechanical components, is very important for their safe and economic operation. Vibration diagnostic algorithms in HUMS analyze vibration signatures associated with faults and quantify them as condition indicators (CI) to predict component behavior. Vibration transfer paths (VTP) play important roles in CI response and are characterized by frequency response functions (FRF) derived from vibration signatures of dynamic mechanical components of a helicopter. With an objective to investigate the difference in VTP of a component in a helicopter and test stand, and to relate that to the CI response, VTP measurements were recorded from 0–50 kHz under similar conditions in the left and right nose gearboxes (NGBs) of an AH-64 Apache and an isolated left NGB in a test stand at NASA Glenn Research Center. The test fixture enabled the application of measured torques – common during an actual operation. Commercial and lab piezo shakers, and an impact hammer were used in both systems to collect the vibration response using two types of commercially available accelerometers under various test conditions. The FRFs of both systems were found to be consistent, and certain real-world installation and maintenance issues, such as sensor alignments, locations and installation torques, had minimal effect on the VTP. However, gear vibration transfer path dynamics appeared to be somewhat dependent on presence of oil, and the lightly-damped ring gear produced sharp and closer transfer path resonances.
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