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Case Study

Fred Hartman Bridge – TxDOT, Texas USA

Texas has more than 53,000 bridges, the largest bridge inventory in the United States.

The Texas Department of Transportation (TxDOT) conducts routine inspections of most bridges every two years, ensuring all bridges open to vehicular traffic in Texas are safe and best in class.

Project Details

Services
SoundPrint® Acoustic Monitoring
Monitoring system commissioned in 2002
Operated continuously since commissioning
Bridge Type
Fan arranged cable-stayed bridge
Monitored Length
2473 ft (754 m)
Number of Stays
192
Stay Type
Grouted 15mm x 7 wire strands in HDPE tubes

Project Highlights

System has performed in excess of 98% of efficiency over its life

SoundPrint identified individual wire events in stays ranging from 50 to 193 m in length

Allows TxDOT to establish remaining service life of 192 stays

Challenge

The Fred Hartman Bridge, located in Baytown Texas, 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 2473 ft. (754 m) long, consisting of steel girders and transverse beams, and includes a 1250 ft. (381 m) main span. ­ The bridge consists of two 78 ft. (24 m) wide composite concrete decks suspended from diamond shaped concrete towers using a total of 192 stays. ­The stays are comprised of multiple 0.59 in (15 mm) seven-wire strands grouted inside HDPE tubes.

After the bridge completion, large-amplitude vibrations of the cables were observed. A vibration monitoring program confirmed that the stays are subject to wind/rain-induced vibrations, raising concerns about potential fatigue failure of the strands.

Solution

Following testing by the Ferguson Laboratory at the University of Texas, TxDOT installed a SoundPrint® Acoustic Monitoring System to monitor wire break activity within the stays. ­

The installation consisted of three specially-designed sensors on each stay (one on each anchor and one on the stay approximately 8 ft. (2.5 m) above the deck). ­ 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 with sensors from each zone 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 center 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® website. As the bridge is located in an area with frequent thunderstorms, the system has been upgraded with state-of-the-art lightning protection technology.

Results

TxDOT personnel have inspected some of the stays based on the reported wire events via anchorage investigations and stay force evaluations. To date, the inspections have not revealed significant changes in the measured stay forces due to the individual wire failures. ­ The rate of wire breaks has given TxDOT confidence in the operation of the stays, as well as the vibration damping system installed to reduce cable fatigue.