REQUEST
The Fred Hartman Bridge is a twin deck cable-stayed bridge with a main span of 381 m (1,250 ft) and two adjacent spans of 146 m (479 ft). Each of the decks is 24 m (79 ft.) wide and consists of precast concrete slabs on steel girders and floor beams. The decks are supported by a total of 192 cables, arranged in four inclined planes originated at each of the two double diamond shaped towers. The towers are 130 m (426 ft) tall. The stays range from 60 to 197 m (194 to 646 ft.) in length, with varying diameters. They are connected to the decks at 15 m (49 ft.) intervals.
The customer, Texas Department Of Transportation, was in need of information related to the structural behavior under violent wind conditions and how the cable tension would react.
SOLUTIONS
S-lynks: a precise and global modal representation of the structure (OMA) without artificial external shake has been deployed by Geocomp, a Sercel company in USA, to the main span, towers and cables of the Fred Hartman Bridge.
S-lynks is designed to detect structural degradation mechanisms that can’t be detected with a visual inspection or other solution.
Geocomp provided the data collection, processing, and reporting within a few days and without the need for excessive field work. The reported information
included:
• Assessment of the resonant frequencies, associated damping and modal shapes of the vibration modes of the deck
• The baseline structural assessment of the main span, tower, and cables
• Cable tension estimation
• Comparison of measured tension vs. design tension and comparison of tension from symmetrically positioned cables
• Evaluation of the external dampers efficiency and performance
CONCLUSION
The customer defined that some cables were having lower or higher tension compared with normal calculation. The consequence is an asymmetry on the deck and tower. The corrections have been made and the bridge is in safer condition for overall structural performance and for the safety of the public. This project highlighted how S-lynks is powerful by the ease of use and it's accuracy.
We were capable to determinate any unusual shapes of dynamic motion for further investigation.
