Crews lower the crossbeam truss following completion of crossbeam construction.
The St. Croix Crossing that will connect Oak Park Heights, Minn., and St. Joseph, Wis., will be open to traffic in the fall of 2017 when crews from the joint-venture of the Lunda Construction Company and Ames Construction Inc. complete the substantial construction project. The $617 to $646 million project also is a shared initiative between the Minnesota Department of Transportation (MnDOT) and the Wisconsin Department of Transportation (WisDOT), with MnDOT being the lead partner.
The 3,200 ft. (975.4 m) extradosed bridge — a design between a box-girder and a cable-stayed bridge — crosses the federally protected St. Croix River and the goals of the project are three-fold — provide a safer, more reliable river crossing, improve traffic safety and ease congestion in the St. Croix Valley; and support jobs and help interstate commerce. Similar bridges include Connecticut's I-94 Pearl Harbor Memorial Bridge in New Haven, Vancouver's North Arm Bridge and Japans Twinkle Kisogawa Bridge.
Work on the project began in April 2013 and the new bridge is expected to carry 24,000 cars and trucks on a daily basis.
“The planning process started several decades ago and there were plans completely developed in 1995 however permits were not able to be acquired,” said Kevin Western, MnDOT's design manager. “The large stakeholder group was involved in all aspects of the project — environmental, location, bridge type, aesthetics etc. The consensus building process led us to the project we are constructing. We are meeting the goals determined from that process. The bridge is designed for 100- year service life. The extradose design was determined, as part of the stakeholder process, with the understanding that this type was new to the United States. The bridge architecture reflects the unique natural setting for the project and we believe will be a landmark structure for the region and both states.”
The new bridge will replace the existing Stillwater Lift bridge, which is being upgraded to a bicycle/pedestrian use only while still accommodating boats underneath. The new bridge foundation and superstructure is expected to cost around $376 million, while the Minnesota approach work is approximately $70 million (Highways 36 and 95) and the Wisconsin approach is $24 million (Wisconsin 64). The funding for the project has many sources, including federal, state and local funding and is dependent on the component of the project. The federal government portion is anticipating a contribution of 80 percent, with the DOTs providing the remaining 20 percent.
The original plan was to open the bridge in 2016, but last September both DOTs and the construction J-V announced the delay in construction. The completion date had been set for fall 2016, but was felt to be unattainable.
“This new date is well within the project team's capability to meet,” said Michael Beer, MnDOTs St. Croix Crossing project director. “It is a large and complex project, and we want to be sure that it is done safely and meets our high standards for quality. We're committed to working with the Lunda/Ames Joint Venture to complete the Crossing project in the most efficient and cost-effective manner possible.”
He adds that the roadway portions of the project remain on track and that improvements to Highway 36 in Minnesota and Highway 64 in Wisconsin, which will connect to the bridge, are either complete or on-schedule to be completed.
Terry Zoller, MnDOT's Construction manager, points out that throughout the construction process, the project has faced a variety of challenges from a worker shortage to weather delays.
“The strengthening regional economy made it challenging for the contractor to find enough skilled and experienced workers for the project,” he said, “and during the 2015 construction season, the segment shuttle crane at Grey Cloud casting yard broke down several times, delaying the movement of segments onto the barges. Each breakdown caused delays lasting from one day to one week.
“Last July,” he said, “the segment lifter broke down on Pier 9, so segments couldn't be erected. This caused an additional week-long delay. Much of this specialized equipment is unique to this project. The complexity and size of the bridge has slowed progress both at the casting yard and on the river. One of the main factors affecting progress is the fabrication and installation of the segments with stay cable connections. The details are more complex (which takes longer at the casting yard) and the installation procedures of the segment, supporting elements, and stay cables are multifaceted.”
Material shortages also have affected the project.
“Acquiring the necessary concrete forms to make the segments for the bridge was delayed five months in 2014,” said Zoller. “Only two American companies make these forms, and the selected company's owner died and the company subsequently lost its lead engineer. The timing of these events caused the company to delay fabrication of the forms.”
Minnesota construction seasons typically last from mid-March to mid- December due to the weather, but in the spring of 2014 the St. Croix River experienced high water levels — a key time in the construction of the bridge piers.
“The high water caused a two-week delay,” said Zoller, “and progress was further slowed in 2014 when winter arrived early. This year's relatively mild winter has helped improve the schedule. Everyone is working hard to meet the new deadline. Work has continued through the winter on cast in place portions of the bridge and the relatively warm weather and lack of snow has enabled crews to continue work more efficiently. Crews have also been able to keep the river ice-free out to Piers 10 and 11 to complete the final tower installations.”
Much was accomplished by the end of 2015. All the crossbeams were constructed, which required the use of 478,000 tons (433,634 t) of rebar and 5.2 million lbs. (2.3 million kg) of concrete — the equivalent of 130 truck loads at each location. Cemstone provides all of the concrete for the cast in-place portions of the bridge and for the on-site casting yard. Aggregate Industries provides concrete for Unit 3 segments at Grey Cloud.
Three of the five river piers have been completed and work on the Pier 13 column began last fall. Just over half of the bridge deck segments have been placed at Piers 8 and 9. Thus far 28 of the 160 stay cables have been installed, with one stay consisting of 76 steel strands bunched together. Each strand is stressed to a force of more than 32,900 lbs. (14,923 kg).
“The Loop Trail is a 4.7-mile bicycle and pedestrian trail,” Beer said, “and when the new Crossing is complete as planned, vehicle traffic will be re-routed onto the new bridge and the existing Stillwater Lift Bridge will be converted to a bicycle and pedestrian facility. The Loop Trail will cross the St. Croix River at the Stillwater Lift Bridge and on the new St. Croix Crossing bridge. Trails in Minnesota and Wisconsin will complete the loop and connect to regional and local trail systems. The lift bridge will still need to accommodate boat navigation with lifts.
“The Loop Trail consists of a number of segments that will be completed by 2019,” he said. “The main portion of the Minnesota Loop Trail will be constructed in 2015 and 2016, with final connections starting in 2018. Construction of the Wisconsin portion of the project will occur in 2017.”
The bridge deck is being constructed in several stages, based on crossbeam construction, pier table construction and driving surface segment installation. The on site casting yard is adjacent to the bridge on the Minnesota side and nearly 340 pre-cast segments are being trucked from the casting yard to the bridge area and about 650 pre-cast segments are being barged to the construction site from the Grey Cloud Island casting yard in Cottage Grove, about 33 mi. (53.1 km) away.
The new river crossing will be made up of five crossbeams, one at each pier location.
“The pre-cast concrete segments, which make up the driving surface, frame into each crossbeam and carry all of the bridge superstructure load back to the piers,” said Beer. “Crews install a temporary truss system to support construction efforts, forms are then fitted in the shape of the crossbeam and iron workers place steel reinforcement bar and post-tensioning tendons by hand within the forms. Crews then pour wet concrete on site into the forms and over the rebar and tendons. These steps are repeated three times —because of the size and detail of each crossbeam, they are constructed in three stages. Then they remove the forms once the concrete has cured to its desired strength and the steel bars and strands inside the structure are tensioned, or pulled like a rubber band, in both directions of the crossbeam.”
Constructing the pier table is the next step in the bridge deck construction process and together with the crossbeam, it forms a large, flat surface above the pier columns. The top of the pier table is the actual driving surface.
The pier table construction uses a cast-in-place design.
“Forms are fitted on each side of the crossbeam in the shape of a segment,” said Beer, “with each side 15-feet wide. The iron workers then place steel reinforcement bar and post-tensioning tendons by hand within the forms. The next step crews pour wet concrete on site into the forms and over the rebar and tendons. This process is repeated several times to construct the bottom, top and side walls of the pier table — the structure has hollow space in its center, similar to the pre-cast segments that are made off site. The workers will remove the forms once the concrete has cured to its desired strength.”
The driving surface of the new river crossing and its approach ramps will be constructed in two ways, using both pre-cast segments and a cast-in-place approach. About 340 pre-cast concrete segments made at the on site casting yard will form the driving surface for the bridge approach spans in Minnesota.
“The new St. Croix Crossing will be made up of about 1,000 pre-cast segments,” said Zoller, “which are being cast off site at two casting yards.”
The Grey Cloud Island yard is producing about 650 segments for the main river bridge and the average size of each segment is 48 ft. (14.6 m) wide, 18 ft. (5.4 m) tall, and 10 ft. (3 m) deep. At the on site yard near the Highway 36/95 interchange, nearly 340 segments are being constructed for the approach/ramp bridges on Minnesota land.
“These segments are smaller than the river bridge segments,” said Zoller, “with the average size of each segment being 43 feet wide, 10-14 feet tall and 10 feet deep and weighing between 80 to 90 tons each.”
Some of the bridge ramps' driving surface is made up of cast-in-place box-shaped sections instead of using pre-cast segments. The first step for Lunda/Ames Joint Venture crews is to install the falsework and then use that to install the shape of very long segments, which vary in length depending on the approach span under construction.
“The iron workers then place steel reinforcement bar and post-tensioning tendons by hand within the forms,” said Beer. “Crews pour wet concrete over the rebar and this is repeated several times to construct the bottom, top and side walls of the structure.
“The stay cables are located above the bridge's driving surface and they anchor to the pier tower on one end and a stay segment on the opposite end. The stay cables help support the load on the bridge and are necessary to have 600-foot spans between the river piers.
“Each cable consists of 76 plastic-coated steel strands bunched together inside a pipe,” said Beer. “The upper part of the pipe is high density polyethylene and the lower part is stainless steel. The pipes are assembled on the bridge deck then raised into position, with each strand strung through the pipe by hand and each strand after it is installed, is stressed from inside the bridge using a hydraulic jack that applies 33,000 pounds of force. The cables and anchorages are sealed to prevent corrosion to maximize their lifespan.”
The design has eight stay cables sticking out from each side of the pier towers and each pier location on the river will have 32 total stay cables. The total length of stay cables is 5.2 mi. (8.3 km) (about 400 mi. of cable strands) and each cable has a total stressing force of 2.5 million lbs. (1.3 million kg).
The work on the Pier 13 foundation pile, located on the Wisconsin Bluff, is no piece of cake.
“Like the river piers” said Beer, “this pier will consist of two columns to support eastbound and westbound traffic. Lunda/Ames Joint Venture is using a top-down construction approach to decrease the impact on the bluff. Construction crews have constructed a temporary trestle to allow them to get crews and necessary equipment out to the Pier 13 work site. They also are limited to 10 ft. (3 m) of tree removal on each side of the bridge to prevent soil erosion and to help the bridge blend into its surrounding environment.
“All of the bridge foundations/footings below the water surface were completed in 2013,” he said. “There are two concrete footings at each of the five piers in the water. At the end of 2013, they raised up about 15 feet above the water level and today they are much higher.”
The roadwork for the Wisconsin approach work will be complete in 2017 when the Crossing opens to traffic. Work done in 2015 includes: grading from just north of County Road E to WIS 64; grading, paving and incidentals on the relocated County Road E; constructing the interchange bridge at County Road E: and constructing the roundabouts at the new WIS 35/County Road E intersection and at the interchange location.
The Minnesota approach road work was completed last summer and that included: reconstructing and realigning Hwy 36 and Hwy 95; directly connecting Hwy 36 and Hwy 95 with ramps and traffic signals; adding turn lanes at the Osgood and Greeley/Oakgreen intersections; realigning the Hwy 36 intersection at Greeley/Oakgreen; creating a shared center turn lane on the north and south frontage roads; adding a trail along the South Frontage Road to connect to the new Loop Trail; adding ponds to improve storm water runoff and water quality; extending the South Frontage Road to Stagecoach Trail, reconstructing the Beach Road bridge; adding traffic signals, lighting, signing and pavement markings; implementing a new Intelligent Transportation System that includes cameras and traffic detection; and the relocation of utilities.
A unique feature of the project is a passage for cattle that is located on the Wisconsin side.
“The farmer's grazing activity required cattle access to his parcels on both sides of the freeway,” says Beer. “The cattle pass will allow the farmer to functionally use that field as he would have before the project.”
Protecting the river during construction from falling debris is a priority.
“The contractor provides a secondary containment under vehicles or machinery on the river,” said Beer. “If leaks occur, oils or other fluid are contained and removed before entering the water. To date the additional steps have been very successful.”
For the most part Lunda crews, about 300 Joint Venture and subcontractor personnel, are working day shifts from Monday to Saturday, with night work scheduled at the casting yards. Some of the major subcontractors include: E&J Steel for all the iron work, and Cemstone and Ag Industries for the concrete.
Equipment-wise, all the standard vehicles and specialized pieces used for road and bridge construction can be found at the various work sites. The Joint Venture is working closely with the DOTs and providing suggestions for the design and to help reduce costs.
“As an example,” said Beer, “the installation of the segments and the stay cables has a very prescriptive installation procedure. That procedure, as followed in 2015, took longer than anticipated. The contractor and engineers are analyzing procedure changes that will reduce time.”
This is a major project for both DOTs and MnDOT is using the opportunity to have its new engineers and inspectors gain experience on such initiatives.
“The experience gained by our employees, especially those newer to MnDOT,” said Zoller, who has been with MnDOT since 1972, “will provide knowledge and confidence to incorporate lessons learned into other projects, as well as shape future policy and practices in the department. Preparing the next generation of leaders for our department is a key piece of our charge. Hiring, mentoring, and supporting the future leaders is essential.”
Beer, currently in Gothenburg, Sweden, is giving a presentation on the St. Croix River Crossing project to the Bridge Builder Day conference. This is the only English presentation at the conference, which had the organizers contact MnDOT to request Beer's appearance and expertise on how transportation authorities can take advantage of this bridge building method.
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