Development of a Substructure Instrumentation System at the New I-10 Twin Span Bridge and Its Use to Investigate the Lateral Behavior of Batter Piles

Recent advances in sensor and smart material technology can be used to provide real-time data for structural health monitoring of bridges. This paper describes a substructure instrumentation system that was installed at a selected pier of the new I-10 Twin Span Bridge over Lake Pontchartrain in Louisiana. The system was designed for both short-term and long-term health monitoring of the bridge. The monitoring system includes instrumenting eight piles with inclinometers and strain gages, and instrumenting the pile cap with corrosion meters, water pressure cells, tiltmeters and accelerometers. A lateral load test was designed and conducted to investigate the lateral behavior of the pier and to assess the validity of the analysis method used to design the batter pile foundations using the FB-MultiPier software. Two high strength steel strand tendons were used to impose about 1900 kips of lateral load. An automated survey station with prisms monitored the horizontal movements of the pier caps and bents. The strains and deformations within the foundation piles were measured using the inclinometers and strain gages. The results showed that the success rate of train gages and inclinometer sensors instrumentations were about 70%. A comparison of results from the lateral load tests with those from the FB-MultiPier software analyses showed that the software analyses had much higher conservative values compared to the measured values. These variations between measured and predicted values demonstrate the need to evaluate the applicability of the FB-MultiPier system for the design and analysis of batter pile group-cap systems. The soils’ p-y curves at different depths were also backcalculated from the derived soil reaction and lateral deformation profiles at different load increments.

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