|Service:||SoundPrint® - Bridges|
|Client:||Texas Department of Transportation (TxDOT)|
|Type of Bridge:||Fan arranged cable-stayed bridge|
|Length:||4.185 kilometres (2.60 mi)|
The Fred Hartman Bridge was opened to traffic in 1995 and is one of the largest cable stayed bridges in the United States. The cable stayed bridge portion of the bridge is 754 m. long, consisting of steel griders and transverse beams, and includes a 381 m. main span. The bridge consists of two 24 m. wide composite concrete decks suspended from diamond shaped concrete towers using a total of 192 stays. The stays are comprised of multiple 15 mm. seven-wire strands grouted inside HDPE tubes.
After the bridge was completed, large-amplitude vibrations of the cables were observed. A comprehensive vibration monitoring program confirmed that the stays are subject to wind/rain-induced vibrations. The evidence that the stays are subject to large-amplitude, low-cycle vibration raised concerns about potential fatigue failure of the strands. Following comprehensive testing by the Ferguson Laboratory at the University of Texas at Austin, TxDOT decided to install a SoundPrint® Acoustic Monitoring System to monitor any wire break activity occuring within the stays.
The installation consists of three sensors on every stay (one on each anchor and one on the stay approximately 2.5 meters above the deck). Specially-designed acoustic sensors were used. These sensors are suitable for cable stayed bridges and are durable enough to withstand harsh marine environments. The bridge is divided into 16 virtual monitoring zones. The sensors from each zone are connected to an active junction box using durable coaxial cable. The active junction box outputs are connected to the SoundPrint® data acquisition and management system (“DAQ”) by means of multiple twisted-pair shielded cable. The DAQ is located inside the North-East tower leg at deck level.
Data is automatically transmitted from the DAQ through a local Internet connection to the Pure Technologies data processing centre in Calgary, where the data is analyzed and classified. On-demand reports are available to authorized individuals through a secure password-protected area of the SoundPrint® web site. As the bridge is located in an area with a high frequency of severe thunderstorm activity, the system has been upgraded with state-of-the-art lightning protection technology.