New bridge for Cowtown

The world’s first precast network arch bridge, featuring 12 arches, is changing the landscape of downtown Fort Worth, TX. The West 7th Street Bridge is the first-of-its-kind and will serve as a gateway to the city’s cultural district, where buildings designed by luminaries such as Louis Khan, Tado Ando and Renzo Piano line the landscape.

“The West 7th Street Bridge design and construction techniques are further examples of Texas leading the way in innovation,” says Texas Department of Transportation Executive Director Phil Wilson. “In addition to being an architectural and engineering landmark for the city of Fort Worth, this precast network arch bridge is a safe, sound and high-quality structure that will benefit both motorists and businesses.”

The new $26 million West 7th Street Bridge, which replaces its 100-year-old predecessor, is a unique and beautiful design that offers much more pedestrian access, Wilson says. The new bridge features a series of sculpted network arches and modern architecture.

TxDOT has a history of building durable, high-strength, precast concrete bridges quickly and at costs that consistently rank among the least in the nation, according to Wilson. The innovative design of the Fort Worth bridge met the challenges of quick construction, aesthetic beauty and improved mobility and safety while also providing a large hydraulic opening to mitigate flood conditions, the agency says.

Precast technology

“The idea was to turn to our successes in precast technology and mass production – only, we knew we wanted something more attractive for the West 7th Street Bridge,” says TxDOT Structural Engineer Dean Van Landuyt. “Aesthetics were paramount.”

The contractor, Sundt Construction Inc. of San Antonio, began work over a year ago. The first year of bridge construction caused little to no impact on motorists and businesses. The arches were constructed at a nearby casting yard donated by Chesapeake Energy.

Each arch is 163.5 feet long and weighs 300 tons. Within the arch, there is a network of stainless steel hangers with clevises and tie-beam connections that protect pedestrians from traffic on the bridge while allowing both motorists and pedestrians to enjoy a nearly unobstructed view of the river.

This new construction method is expected to result in seven fewer months of bridge closure compared to a typical 12 months or more using traditional methods, TXDOT says.

Key to the construction of the West 7th Street Bridge was the innovative rigging plan and performance of crews from Columbus, MS-based Burkhalter Rigging.

Burkhalter Rigging crews were responsible for the lift, rotation and storage of the arches as they were cast, as well as the transportation of the arches to the bridge site and then lifting and setting of the arches into place, according to Delynn Burkhalter, president.

The arches were constructed on a site about a mile away from the actual bridge. The concrete arches were cast in groups of two.

After each set of two arches was cast, Burkhalter used its “Mini-BSET,” a hybrid tower gantry system, to lift, rotate and slide each arch into a storage location on the construction yard. Burkhalter started work at the pre-cast and storage site in August of 2012.

Set up over the area where the arches were cast in place, the BSET carefully lifted and rotated the arches to an upright position. It took about 3.5 hours to lift and rotate each arch upright and into position for storage.

All of the arches were completed and stored by February 2013. In May, the old bridge was shut down to traffic. Once the new bridge columns were in place, Burkhalter crews began the transportation of the arches over the decaying 100-year-old existing bridge to the site and setting them onto their supports.

Remote controlled SPMTs

“Each arch was transported from the construction yard to the bridge site via self-propelled mobile transporter,” says Burkhalter.

Using remote controlled operation of the SPMTs, crews slowly maneuvered each arch into position. The arch was then rigged so the cranes could pick it up and set it on its support columns. Once both cranes had the weight of the arch on its hooks, the SPMTs were driven out from underneath it.

“They were lifted off the SPMT, positioned and set onto concrete columns using two Liebherr LR1400 crawler cranes, each rigged with superlift attachments,” Burkhalter says.

The setting of the arches, and subsequent assembly/disassembly/movement/reassembly of the cranes was a continual process from May until mid-June when the last arch was set in place. Six arches were placed along each side of the bridge.

The cranes had to be repositioned eight times. The arches were mostly placed in sets of two, with two arches set every four or five days. Burkhalter had to work around a variety of obstacles, including road closures, poor ground conditions, a multitude of utilities, and tight contractor scheduling windows.