LeJeune Flyover was built to ease traffic congestion leaving the Miami Airport going westbound to the City of Hialeah by connecting LeJeune Road northbound to Okeechobee Road westbound. Approximately 33 ft wide and 262 ft long, the Flyover is designed to carry two lanes of vehicular traffic. The superstructure is supported on two piers and consists of a twin, steel box girder bridge with an 8 in. cast-inplace composite deck. One of the piers, Pier Two, has a cantilevered arm that gives the pier an L-shape and is set on a footing that is below grade. The second pier, Pier Three, is a hammerhead, T-shaped pier.
A few months after the bridge deck was constructed, an inspector discovered cracks in the pier resulting from construction loads. Horizontal cracks uniformly spaced at about 12 to 18 in. were observed on Pier Two. In addition "V" shaped cracks were also discovered in the pier cap of Pier Two and Pier Three. The Florida Department of Transportation (FDOT) concluded that these cracks would continue to deteriorate over the years and cause long-term maintenance issues. It was necessary to immediately repair the cracks.
Upon review of the details in the as-built construction documents, it was determined that the horizontal cracks on Pier Two were caused by a rebar detailing error. The vertical reinforcing steel in the column was not properly lapspliced with the top steel in the pier cap thereby causing horizontal cracks. The "V" shaped cracks in the pier cap were caused by insufficient top reinforcing bars. This also was the case for Pier Three, which had insufficient reinforcing steel in the pier cap.
The FDOT wanted to ensure that the structure would have a service life of at least 75 years. As such, they required the solution to be durable, cost-effective and aesthetically pleasing. The bridge was located over a canal, which created a moderately aggressive environment. As such, the repair solution also had to be resistant to possible corrosion. Additionally, it was important that the repair method for the horizontal cracks not require enlargement of the pier as this would require excavation around Pier Two below the water table. There was concern that a cold joint below the water table would make the reinforcing steel susceptible to further corrosion and reduce the service life of the structure. Excavating the foundation at Pier Two would also dramatically add to the time needed to complete the repairs and significantly increase the cost. It was recommended that the post-tensioning tendons be placed into vertically drilled holes and encased in concrete after stressing. This would replace the vertical reinforcement in the pier and close the horizontal cracks. Horizontal post-tensioning was proposed to reinforce the pier caps. To enhance durability and improve aesthetics it was decided to increase the size of the pier cap and encase the post-tensioning tendons in concrete for Piers Two and Three.
REPAIR PROCESS
Two 5.5 in. diameter cores 40 ft long were drilled from the top of the pier cap - stopping a few inches from the bottom of the footing. Cores were extracted in 12 in. increments until the appropriate depth was reached. The posttensioning tendons were then lowered into the hole and grouted in two stages. The first stage consisted of grouting the post-tensioning tendons for a length of 15 ft to provide the "bond length" for the anchorage. The tendon was then stressed from the top with a specially modified hydraulic jack. The second stage of grout was then pumped into the remainder of the hole. Special low bleed pre-packaged grout was used to grout the holes to encase the tendon and provides corrosion protection.
Repair of the "V" shaped cracks at the pier cap and column connection on both Pier Two and Pier Three required casting an enlarged section of concrete on both sides of the pier cap. High-strength, horizontal post-tensioned bars were cast in the concrete section to reinforce it. Rebar dowels were used to connect the new concrete to the old concrete. The post-tensioned bars were stressed to provide active compression to the pier.
The LeJeune Flyover demonstrates the repair team's effectiveness for developing innovative solutions to complex problems. Before this project began, the road had been under construction for nearly two years, so it was critical that the project was completed in a timely fashion with minimal impact. By developing an open working relationship with the owner, innovative solutions were developed and the contractor was able to provide a turnkey solution that included repair design services, labor resources and shop drawings. Repairs were completed two weeks ahead of schedule and were delivered using the most cost-effective solution. The field portion of this extremely fasttracked project was completed in a mere four weeks - allowing the flyover to be opened ahead of schedule.