Precast concrete plays an important role in replacing a historic bridge on a busy trade route while protecting area wildlife.
By Shari Held
Located in the scenic Badlands of North Dakota, the historic Long X Bridge pays tribute to the Long X Ranch and Cattle Drive that epitomize the state’s western heritage and culture. Built in 1959, the two-lane truss bridge spans the Little Missouri River along U.S. Highway 85, just south of Watford City. This stretch of highway is part of the heavily traveled Ports-to-Plains Corridor, which extends from Texas to Canada. It also runs through the “Bakken,” one of the largest oil developments in the U.S.
Designing the future
Trucks carrying oil, agricultural products and other trade items traverse the Long X Bridge daily, and traffic counts continually increase, which has created challenges for the 61-year-old bridge. Equally problematic, the bridge’s maximum allowable vehicle height isn’t high enough to accommodate modern vehicles, which has resulted in the bridge being hit and closed numerous times.
“I personally get phone calls when that bridge is shut because it means a 70-mile-plus detour,” said Jon Ketterling, P.E., state bridge engineer for the North Dakota Department of Transportation (NDDOT).
The go-ahead to build a wider bridge with no height restrictions was given in 2019. The $34 million project also includes a new wildlife crossing. Work is underway on a four-lane replacement bridge approximately 25 feet east of the existing bridge, which will remain open during construction. The new bridge, which will retain the original name, will be supported by 60 precast I-beams.
The I-beams, supplied by Forterra Pipe & Precast, were designed with the ability to transport in mind. At 156 feet long, the beams were the longest the Menoken, N.D., plant had produced, but it was the sharp turns in the roadways between the plant and the construction site that presented a greater concern.
“(We had to) take into account transportation during the design phase because there can be quite a bit of torque on the beams, and longer beams are fairly flexible,” said Dale Schwindt, P.E., project engineer with Forterra Pipe & Precast, Menoken, N.D.
Producing the I-beams
Fabrication of the prestressed beams began in September 2019. Forterra’s Elk River, Minn., plant manufactured 24 beams, and its Menoken, N.D., plant manufactured 36.
A high-strength, easy-flowing concrete mix with a specified 28-day compressive strength of 9,000 psi was used for the beams. The plant made special accommodations to take into account the cold weather. Schwindt said the plant kept the beams in the casting beds and steam cured them overnight to ensure the proper strength gain.
Bringing the bridge to life
Safety has been top-of-mind for Tyler Davis, on-site project manager for general contractor Ames Construction, headquartered in Burnsville, Minn. The crews are working over water, around live traffic and in close proximity to the Theodore Roosevelt National Park, which means plenty of wildlife in the area.
Erecting the bridge’s substructure, which includes four piers – two in the middle of the river – wasn’t easy. Ames Construction had to build cofferdams and causeways so workers could access the piers. This required detailed scheduling coordination with the delivery of the I-beams to the job site, which the precaster was able to accommodate.
Forterra’s Elk River plant shipped its 24 I-beams during December 2019 and January 2020. Each beam measures 81 inches tall, 156 feet long and weighs 75.6 tons. On the job site, cranes arranged the initial 12 I-beams to create the first of five spans. The first span was installed in January 2020, prior to the winter shutdown. According to Davis, the installation went seamlessly.
Designing the wildlife crossing
In addition to the bridge, the project includes a wildlife crossing. The area’s bighorn sheep are the rarest North Dakota big game species. Numbering around 330, they roam the Badlands along the Little Missouri River. With the expansion from two lanes to four lanes of traffic, ensuring the safety of the bighorn sheep, along with the safety of the traveling public, is a major concern.
NDDOT partnered with Contech Engineered Solutions, headquartered in West Chester, Ohio, to create a wildlife crossing dedicated to North Dakota’s bighorn sheep population. While the crossing is a first for NDDOT, Contech has extensive experience with wildlife crossings nationwide. The wildlife underpass crossing will be located about 900 yards south of the new bridge.
Timothy Miller, Structures Area Manager for Contech Engineered Solutions, worked with NDDOT, North Dakota Game and Fish and other agencies prior to the bidding process. According to Miller, factors to take into account for this specific wildlife crossing, which required a minimum 40-foot-wide-by-15-foot-tall interior clearance, included topography, road dimensions, vegetation and climatic conditions.
This crossing needed to work with the road grading and the elevation on either side of the roadway. It also had to accommodate enough fill between the top of the structure and the roadway surface for sound dampening and be large enough for the sheep to use it. In addition, the location had to be one where bighorn sheep would normally cross.
Precast: the best solution
A buried, three-sided bridge built with precast concrete was selected for several reasons. By using precast, the wildlife crossing can be built with a wide enough clearance that a guardrail would not be necessary. Using precast also enables the project to be built in phases. Phase 1, which consisted of 30 arch pieces (90 linear feet of structure), was installed in late April, and the area was backfilled through late May. NDDOT moved traffic to the finished half while completing the remaining portion.
Post-construction soil settlement was a big concern during the design phase, so the precast structure will rest on a driven steel pile foundation topped with cast footings that will run perpendicular to the highway.
Once completed, 50 precast elements will make up the 60-foot-span-by-18-foot-rise-by-150-foot-long BEBO arch structure, with each precast piece weighing 20.4 tons. The precast arch units required a minimum compressive strength of 6,000 psi to meet the loading criteria. To create the arch, two half-arch elements are installed at opposite, parallel footings. At the peak of the arch element’s rise, in the center of the span, each of the two half arches have a recessed cavity with temporarily exposed reinforcement. The elements are bolted together, and the cavity is filled with high strength concrete on-site to complete the connection. This modular approach allowed the structure to be constructed quickly. It took only three days to install the elements for Phase 1.
“The speed of installation of the arch itself is also a factor in minimizing the amount of detour time of a heavily trafficked highway,” Miller said.
Almost ready for business
The bridge is slated to open at the end of 2020, and the entire project, including disposal of the existing bridge, will be complete July 2021.
“The Long X Bridge has served the public well for over 60 years,” Ketterling said. “As with everything, there comes a time when things need to be replaced. The new bridge will meet the needs of the traveling public and industry both now and well into the future.”
Shari Held is an Indianapolis, Ind.-based freelance writer who has covered the construction industry for more than 10 years.