Articles / June 4, 2024

Rail Infrastructure Revival: Upgrading the Century-Old Loxahatchee Bridge

The Loxahatchee Bridge project increased rail capacity and improved reliability along the corridor that serves as a key link in the regional passenger-rail service between Miami and Orlando.

The Loxahatchee Bridge project in Florida showcases how ingenuity, collaboration and adaptability were applied to modernize—rather than replace—a century-old bridge to benefit the community and commerce alike. Restoring the bridge to its original full use, combined with many unknown conditions and weakened structural integrity, made strengthening the bridge a formidable task for engineers.

Following extended design holds and after the initial design was completed, a strategic project shift demanded a new approach. The design team was faced with the unique challenge of integrating prepaid and prefabricated steel girders from their original design into the new approach for span-pier replacement.

Background

As part of its $2.7 billion Orlando expansion plan, Brightline set out to strengthen a 100-year-old Florida East Coast Railway (FECR) drawbridge spanning the Loxahatchee River in Jupiter, Fla. The drawbridge, one of three movable bridge structures on the Orlando expansion project, serves as a vital link between south and central Florida, carrying trains across a critical connection point.

Originally built in the 1920s, the 584-foot bridge, which formed part of Henry Flagler’s railroad, comprised nine spans, concrete piers with timber piles and two tracks—one operational while the other long-since decommissioned.

“The Loxahatchee River bridge represents one of the more-complex construction projects along our Orlando extension,” says Michael Cegelis, Brightline’s executive vice president of Rail Infrastructure and Development. “Considerable work was required on the nearly 100-year-old structure to prepare it for high-speed passenger rail. This new structure is another important example of the significant investment Brightline is making to improve Florida’s transportation infrastructure.”

A new construction approach for pier foundations required the contractor to use means and methods that allowed trains to run on schedule. Piles were driven in close proximity to the active track, and operations were required to be complete with piles cutoff below the clearance envelope before trains were allowed to pass.

The Project

Initially conceived as an effort to strengthen the century-old structure, the project aimed to improve reliability, increase capacity and create efficiency in bridge operations. This included improving clearance for boaters and increasing the capacity for modern high-speed rail cars through the addition of a second track. However, the project took an unforeseen turn when a strategic shift took the design from strengthening the existing girders to full superstructure replacement.

The partnership between Brightline and TranSystems proved crucial as they navigated the complexities of redesigning key elements while adhering to strict budgetary and construction constraints. Challenges abounded, from repurposing already fabricated structural steel to accommodating unexpected foundation issues during construction. Through innovative design, engineering and problem solving as well as agile decision making, the project persevered.

The Pivot

“At the time we selected TranSystems, their scope was to perform a comprehensive inspection of the bridge and provide design recommendations for components requiring rehabilitation or replacement,” explains Scott Gammon, Brightline’s senior vice president of Construction.

The bridge was originally designed to carry two parallel tracks. Decades ago, the West track was abandoned in place, and only the East track remained in use. The team completed a load rating to determine the bridge’s ability to carry Cooper E72 loading. Due to the section losses present, the superstructure elements in their existing condition were not capable of meeting this capacity. The extensive section losses present on the steel girders required the steel superstructure to be replaced, rather than Brightline’s original intent to just rehabilitate the steel, which significantly impacted the project budget and delivery timeline.

“TranSystems prioritized redesign efforts at our request, focusing initially on critical long-lead construction elements such as structural steel girders and major mechanical components,” adds Gammon. “This importantly allowed Brightline to expedite steel-girder procurement and accelerate the project schedule.”

This collaborative effort, involving Brightline’s management team and FECR, led to acceptance of TranSystems’ $34 million rehabilitation design and construction plan in 2016. “While Brightline concentrated on design and construction efforts of other key projects in the region, design work for Loxahatchee was placed on hold for a few years,” notes Gammon.

Following the release of the design hold in 2018, TranSystems further assessed the project against current conditions. In addition to structural deterioration, concerns heightened around the potential effects of increasing climate events such as scour, which can endanger foundation stability. Strategically ensuring future resilience, Brightline concluded funds would be better spent in replacing the 100-year-old piers. The new design approach would include new piers as well as replacement of the entire superstructure, mitigating the future risk of costly maintenance and rail-service disruptions.

Redesign Challenges

Upon completing the initial superstructure strengthening design as well as fabrication of the structural steel, Brightline and FECR decided to replace the approach-span substructures. The design team determined only the original abutments, bascule pier and rest pier could be reused.

“When the redesign occurred, the superstructure replacement had been completely fabricated,” explained Steve Shaup, TranSystem’s project manager and Structures Engineer of Record for the bridge. “Since we reused the abutments at each end of the bridge as well as the bascule pier and rest pier that would support the movable span, we looked at ways to reuse the steel spans that had already been bought and fabricated.

“On top of the replacement of the existing approach span piers to ensure the bridge was able to handle modern scour criteria, we had to ensure that the existing piers saw loads no greater than their original design loads from the 1920s,” he adds. “We looked at span arrangements that would reduce the heavier loads that could be produced by both tracks under freight loading. In the end, we provided short jump spans adjacent to the bascule pier and rest pier. This reduced the expected loads in those piers as well as allowed reuse of the original span lengths, allowing for the fabricated girders to be used.”

The front end of the bascule leaf is being lifted into place during short-term full rail and marine outage. Trunnion towers and heel-end alignment was shop tested to document deflections and facilitate installation with minimal alignment adjustments needed after front-end splicing was complete.

The existing bascule span was removed in pieces to maintain rail operations. The leaf’s toe end was
removed, and a temporary flying jump span installed. The jump span was removed twice daily for marine
traffic to pass.

Increasing Passage Capacity

The bridge’s movable span is normally in the raised position unless a train is crossing. Freight trains at the time were crossing no more than a dozen times daily. With the addition of high-speed passenger rail, crossings were predicted to triple in number.

The bascule span in the main channel only provided approximately 6.5 feet of vertical clearance when in the lowered position, severely restricting the size of vessel that could pass while trains were crossing. To address public concerns about the delays boaters would experience with increased operations, Brightline partnered with the Jupiter Inlet District to collaborate with the marine community and obtained a state waterway assistance grant to provide navigation relief. A through-girder span that would provide a shallower superstructure depth was designed to replace one of the existing deck-girder spans, providing an additional 1.5 feet of clearance for smaller pleasure craft to pass through the bridge when the movable span was in the down position.

Geotechnical Challenges

Considering the impact of storm surge and the risk of scouring of the channel bottom, foundation designs accounted for bridge scour to prevent future deterioration. The original piers used timber piles, and little information was known about them. The new foundations were constructed of open-steel-pipe piles, designed with wall thicknesses to accommodate section losses in the highly corrosive saltwater environment. Although the pipe piles were adequate to support the loads, additional redundancy was provided by installing a rebar cage and filling it with concrete to below the scour depth to ensure long-term service life, even if the pipe piles were subject to significant section loss.

Additional geotechnical challenges arose during construction as unexpected pile-driving results necessitated prompt foundation redesigns to accommodate new pile configurations. The geotechnical conditions differed significantly at several of the new pier sites, necessitating a reanalysis of the piers as Pile Driving Analysis (PDA) test results were received. Multiple piers had to be redesigned promptly using various available pipe-pile diameters and with revised spacings to ensure construction remained on schedule.

Construction Sequencing

Construction work was strategically scheduled to minimize disruptions to freight rail and marine traffic. Substructure units were designed to be installed around the active track, ensuring that trains could continue running smoothly. To ensure installation efforts could be completed within approved work windows between trains, the steel-pipe piles were fabricated to length and driven in a single operation. Construction of the new approach span piers didn’t affect navigation.

The design documents and Brightline’s method of procurement emphasized minimizing the amount of time the bridge would be closed to train as well as marine traffic. This provided the contractor with the flexibility to devise its own methods and strategies to operate within this framework.

“The contractor, Scott Bridge Company of Opelika, Ala., developed the concept to provide a removable jump span,” notes Shaup. “The jump span was designed to be ‘flown’ in and out by a crane twice daily over a 45-day period, rather than completely closing the main channel to marine traffic for an extended period of time. The contractor’s concept was to install the permanent replacement bascule span in three sections so trains could operate on the East track via the jump span while the A-frame supports, heel ends of the span, and the mechanical and electrical systems were installed.”

This involved conducting comprehensive dry runs of connecting the three sections in the shop so precise measurements could be taken of the deflections and rotations of the towers when the front section was attached. This allowed the team to precisely align the heel ends onsite and then bolt the front end into place during a 48-hour full bridge closure with confidence that required machinery tolerances could be met.

“During installation of the span leaf, the alignment and bolting up to the heel sections went smoothly—the shop work really paid off,” recalls Shaup. “Getting the span’s electrical system completely cut over to the new system during the outage windows proved to be a challenge. Some elements required alignment adjustments in the field to fit, such as the rest-pier-mounted span locks that had to engage receivers in the toe-floor beam. Work crews planned for last-minute adjustments to ensure all systems were functioning properly and the bridge would operate safely from ‘day one.’”

The bridge has new mechanical and electrical systems, including details and access platforms that will provide for easier and safer accessibility for maintenance personnel, ultimately improving bridge reliability.

The End Result

Given the shift in the project’s scope and complexity, the budget increased to $62.3 million. Brightline and TranSystems took proactive steps to establish a collaborative framework involving the design team, FEC Railway and the contractor. This collaborative approach ensured timely agreement on design concepts and thorough evaluation of proposed construction methods.

“I am most proud of the way our design team worked in partnership with Brightline to address the challenges a movable bridge rehabilitation can bring, working to provide timely, well-thought-out solutions as their needs changed, and being there to supplement their experience with our expertise when they needed it,” states Shaup.

The project restored the bridge to double-track operation, improved reliability and efficiency to the bridge, improved dependability of bridge operations, and delivered additional clearance for watercraft. The addition of a second track not only boosts capacity along the corridor but also strengthens its role as a crucial link in regional passenger-rail service between Miami and Orlando. Moreover, the integration of new spans meeting current codes significantly enhances the FEC Railway’s ability to transport materials and goods efficiently to distribution centers across the region.

According to Lawrence Kirchner, TranSystems senior vice president and bridge practice leader, “With more than 250 experts devoted to customers like Brightline, our movable bridge expertise positioned us well to tackle the Loxahatchee complexities.”

The initial rehabilitation approach was scheduled to be completed by January 2022. Teams rallied around the new replacement plan, delivering the newly designed bridge in September 2023. “Brightline could not be more pleased with the 10-year relationship we have forged with TranSystems on this project,” concludes Gammon. “Their consistent demonstration of true partnership, flexibility and responsiveness were vital to the success of this project.”