What is unique about this bridge? The site designated for the Northaven Trail Bridge required the bridge to be built at an angle across the eight lanes of US 75. The design team decided to create a unique tied arch structure that accommodates the skew and gives the bridge a soft, reverse “S” curve. With tied arches, a bridge deck normally needs to be straight. Within the Northaven Trail Bridge’s S-curve, however, straight post-tensioning strands run through the deck, acting as the tie. The structure is the only known network tied arch bridge in the world with a doubly curved tie. The bridge also has skewed ends, making it an exceedingly complex structure not seen elsewhere in the world. What challenges did the project encounter, and how did HNTB, the contractor and the client overcome them? To meet the challenge of keeping US 75 traffic moving throughout the Northaven Trail Bridge project, the team designed for accelerated bridge construction techniques, which allowed the bridge to be built off-site and moved into place. The bridge deck, cables, and arch were constructed as a single structure on timber shoring in the back parking lot of a furniture store to the east of the highway. Other elements, like bridge columns and approaches, were built in place at the highway. The bridge move, a first for TxDOT’s Dallas district, was achieved over a single weekend. Utilizing remote-controlled SPMTs, the bridge was transported from its off-site location on a Friday in September 2023 and positioned roadside to US 75/North Central Expressway. On Saturday, the SPMTs pivoted the 201-foot-long, 800,000-pound structure from its parallel position before relying on bridge gantries to place the bridge in its final location. TxDOT and HNTB team members stood side-by-side on US 75 in the middle of that night, watching the Northaven Trail Bridge with its 50-foot-tall arch be driven into place over the highway. While highway traffic was minimized for a few hours overnight, the project team was able to ensure that US 75 was never fully closed to travelers. By Sunday afternoon, the bridge was in place and all US 75 lanes were once again open. The bridge move took about 20 hours, requiring only about 14 hours of full closures of the main lanes. During that time, traffic was diverted to the adjacent frontage road, leaving a lane of traffic always open to drivers during the move. After the bridge was installed, final tie-ins were completed before the span opened to the public. How does the completed project fulfill the client’s and the community’s goals? The public was deeply invested in the project and the bridge has been celebrated and heavily used since it opened. The project included dedicated parking on the west side of the bridge for anyone who wants to drive to the site and use the spot as a trailhead. The parking area is designed as a space that can accommodate food trucks, the start of a
race, or other events, enhancing the area’s potential use as a community space. Because the bridge’s arch is its most identifiable feature, it already has become a defining landmark that serves as a gateway into North Dallas. Feedback provided to TxDOT reveals the benefits the bridge has already delivered to the community and confirms that the public appreciates the project’s grandeur. The day the Northaven Trail Bridge opened, “tons of people were using it,” said TxDOT project manager Nathan Petter. “The public was so vested in this wonderful project. The use we immediately witnessed showcases the project’s success.” What are the aspects you would like readers to know or remember about this bridge project? The Northaven Trail Bridge used accelerated bridge construction, a methodology that allowed the bridge to be built near the roadway and moved into place over the eight lanes of US 75 using SPMTs. This technology facilitated the project team’s ability to meet TxDOT’s goal of never fully closing US 75 to travelers. The design team addressed the unique geometry at the site where the bridge now stands by designing a softly curved bridge deck that uses a network tied arch. The bridge’s network cable arrangement, a term used when the cables cross one another more than once, allows the arch and the bridge to be very thin while still being resilient to accidental overloads. The Northaven Trail Bridge is a complex structure that is the only known network tied arch bridge in the world with a doubly-curved tie.
52
csengineermag.com
Spring 2024
Made with FlippingBook Annual report