Structural Evaluation and Condition Assessment - Ford Island Bridge

Structural Evaluation and Condition Assessment – Ford Island Bridge

Intelligent Infrastructure Systems was tasked with performing a detailed structural evaluation of the Ford Island Bridge. Constructed in 1998, the Ford Island Bridge is located in Hawaii and connects the mainland of Honolulu with Ford Island. The structure is nearly a mile long and includes prestressed bulb-tee spans, a steel thru girder span, and a unique movable segmental concrete floating pontoon span. Shortly after the bridge was commissioned, significant levels of deterioration were observed near the waterline of several prestressed concrete piles. An investigation into this deterioration revealed the root cause to be poor concrete quality due to an isolated construction event that potentially affected 41 piles. To mitigate this deterioration, several different repairs were implemented. Due to the nature of the rehabilitation (jacketing), it is impossible to visually appraise the piles and determine whether or not the deterioration has continued to progress. In addition, in the years since the repair, several other performance issues have become apparent related to excessive vibrations and live load rating, as the bridge is planned to be converted from two to three lanes due to the development of Ford Island.

Intelligent Infrastructure Systems also completed a detailed evaluation to assess the current structural performance and identify and classify the key vulnerabilities of the system. The evaluation includes the development of a comprehensive 3D finite element (FE) model and series of parametric studies to fully understand the uncertainties and their influence on performance. To assess the load carrying capacity a thorough load rating (inclusive of substructures) will be performed according to the AASHTO Load and Resistance Factor Rating (LRFR) method, with the demands obtained from the FE model. In addition, two types of field testing will be performed. The first includes global assessment through ambient vibration and forced impact testing of the structure. This information will be used for error screening and calibration of the FE model. The second type of field testing will utilize several nondestructive evaluation (NDE) techniques to measure their ability to assess the condition of the prestressed concrete piles. The NDE techniques to be implemented include ultrasonic surface waves, ground penetrating radar, impact echo, and electrical resistivity. The objective of the NDE is to identify concrete degradation, delimitation, and corrosion of the reinforcement. Overall, the information obtained from the structural evaluation will allow for informed decisions regarding the preservation of the bridge, which includes identifying future inspection and assessment approaches, appropriate time intervals for such approaches, and potential interventions (retrofit, repair, etc.).