With a glass-like river surface, patience and precision maneuvering, bridge workers floated and hoisted a 545 ft. (166 m) long free standing tied arch to its place on the new Hastings, Minn., bridge. Shooting to open the bridge to two lanes of traffic by early summer, 2013, it will have the longest, free standing tied arch span in North America, according to Minnesota Department of Transportation (MnDOT) officials.
The new bridge will replace a 60-year-old arch steel truss structure that is outdated, under capacity and one of the busiest two lane bridges in the state.
The bridge carries TH 61 across the river. The highway is a north/south road that terminates at the Canadian border on the north shore of Lake Superior and runs south near the eastern edge of Minnesota to St. Paul. In St. Paul, it meets with the Mississippi River and follows the river’s western shore line to the southeastern corner of the state and its border with Iowa.
The joint venture of Lunda/Ames broke ground in the fall of 2010 for this project and is building the new, 1,900 ft. (580 m) bridge next to the existing one at an estimated cost of $120 million. Lunda and Ames are both heavy construction contractors specializing in bridge and road construction in the Midwest.
MnDOT is keeping the existing bridge open to traffic while its replacement is under construction.
Located about 20 mi. (32 km) southeast of St. Paul, Hastings is a historic Mississippi River town with a population of around 22,000.
The new bridge will be only the third bridge in Hastings over its 160-year history.
Existing site conditions at the location of the new bridge prevented the arch from being built there, according to Kirsten Klein, MnDOT Public Affairs officer.
“The existing navigational channel directly below the main span prevented shoring towers from being used to erect the main span in-place because the navigational channel would become blocked,” Klein said. “The presence of high voltage lines prevented an overhead temporary cantilever system to support the arch during construction.”
The construction and move of the arch became a project in itself. As bridge workers were well on their way raising the piers and placing the bridge deck, others at a staging area on the riverbank about a half-mi. (.8 m) upriver from the bridge site began building the arch.
With steel shipped in from PDM Bridge out of Eau Claire, Wis., and crane operators picking steel with a Terex HC110 crane and a Manitowac 2250 crane, Lunda/Ames crews completed the arch in early August.
Once completed, Mammoet crews, a Netherlands based company specializing in transporting and hoisting huge loads, moved a mammoth “Self Propelled Motorized Transport” (SPMT) under the arch. Using hydraulic jacks, they gently placed it on the SPMT.
Under the control of one operator, yet guided by numerous pairs of eyes, workers rolled the SPMT and its huge and heavy load to a temporary causeway onto a flotilla of eight barges moored out of the navigation channel.
Meanwhile, Mammoet crews at the bridge site installed large hydraulic jacks and a rail system at each of the supporting piers to guide and hoist the arch in place.
It is the second time in five weeks that MnDOT brought Mammoet crews and their innovative techniques to a state highway project. In mid-August, another Mammoet SPMT crew moved a pair of bridge decks to the recently completed Maryland Avenue Bridge in St. Paul that carries a high volume city arterial street across I35E.
Similar to the Hastings arch construction, crews built the pair of decks at a staging area next to the freeway away from the bridge site. MnDOT engineers estimate the construction time was reduced by 40 percent on this project by using this construction technique.
After many checks to ensure a safe passage, on the first day of fall, traffic crews closed the existing Hastings bridge for a scheduled 72 hours to traffic and the river below to boat navigation. It was the only, long term closure expected for the project.
On that cool, early Saturday morning, hundreds of spectators gathered on the river banks to watch tugboats push the flotilla of barges into the navigation channel with their 330 ton (300 t) and 98 sq. ft. (30 m) high load.
Moving with the slow current, the tugs churned water behind them and reached the open gap in the bridge in less than two hours.
Floating the arch to the new bridge was quick. Once there, however, dozens of workers huddled together on the barges at each pier to begin the detailed, arduous and precise procedure of aligning and pushing the huge arch onto the rail system while tugboat pilots steadied its platform on a moving river.
With very little room to spare and working around the clock and through the night, it took Lund/Ames and Mammoet crews approximately an additional 50 hours to align the arch and raise it to the top of the piers. It will be anchored in place by post-tensioned concrete knuckles and tie girders.
MnDOT staff said overall the arch float went well with some lessons learned, among them securing the bridge to the barges took longer than expected.
With an ADT of 32,000 and sitting 60 ft. (18 m) above the normal river level, the new bridge will carry four, instead of two lanes of traffic on a 100 ft. (30 m) wide deck that will include a 12 ft. (3.5 m) pedestrian and bicycle lane. It will open up a long standing bottle neck for morning and evening commuters, according to MnDOT.
The original bridge in Hastings was constructed in 1895 and featured a spiral deck at its south deck to bring horse and cart traffic directly onto the main street of downtown Hastings. It stood the test of time and history. For the next 56 years it safely transitioned into heavier vehicle traffic and became a Minnesota landmark featured on post cards throughout the state. The spiral deck was also the only known bridge worldwide to incorporate this feature.
The installation of the arch is a major milestone and a historic one for this project, MnDOT officials said. Work will continue through the fall and winter. By late spring next year, MnDOT expects to have the new bridge open to one lane of traffic each direction with a full, four lane opening is targeted for December of next year.
Like the first bridge built here, MnDOT officials are expecting this bridge also to be a landmark structure for the next 100 years.