Award of Merit: Longevity Category
JTA Skyway Double-Tee Beams Restoration
Submitted by Sika Corporation
Jacksonville Transportation Authority
Structural Preservation Systems
Jackson Beach, FL
The Jacksonville Transit Authority (JTA) Skyway is a 2.5 mile (4 km) elevated, automated people-mover system that serves downtown Jacksonville, FL. The Skyway was completed in 2000 at a total cost of $184 million. The guideway was constructed using prestressed concrete double-tee beams supported by concrete ledger beams. Approximately 500 beams were used for the guideway system.
A little more than a year after the last segment of the Skyway was completed, numerous hairline cracks were observed in the precast concrete beams that support the monorail track. After further analysis, it was determined that excessive debonding of the prestressing tendons caused the cracks. A total of 63 beam ends were affected, or approximately 13% of the total number of double-tee beams. A cause for concern, it posed no immediate danger to the Skyway. Nevertheless, some temporary supports were installed while a determination was made on how to repair these cracks. At no time was service interrupted on the system.
After careful consideration, several different repair scenarios were evaluated, including steel plates, external post-tensioning, and carbon fiber-reinforced polymer (CFRP). A ranking system was established, rating the possible repair techniques by criteria such as durability, maintenance, aesthetics, and cost. The solution chosen was CFRP, externally bonded to the ends of the deficient beams to compensate for the strength lost due to the debonded strands. The repair program also included epoxy injection of cracks and installation of a tinted acrylic coating over the CFRP.
The selected repair program not only corrected the construction defect but aslo has now withstood the test of time. CFRP was a relatively new technology 12 years ago. By scientifically considering options available and selecting the optimum method of repair, what was repaired 12 years ago in 2002 is still performing satisfactorily.