The Minnesota Department of Transportation (MnDOT) is spending $13.8 million to rebuild the deck of the Highway 5 bridge/West 7th Street Bridge, an east-west, 1,999-ft. (609.3 m) long span (two lanes in each direction) across the Mississippi River.
The Minnesota Department of Transportation (MnDOT) is spending $13.8 million to rebuild the deck of the Highway 5 bridge/West 7th Street Bridge, an east-west, 1,999-ft. (609.3 m) long span (two lanes in each direction) across the Mississippi River.
The project, which started last April and will be completed this November, is just north of Highway 55 in Fort Snelling and Wordsworth Avenue in St. Paul. The bridge, built 50 years ago, is undergoing work being performed by the Lunda Construction Company to create a smoother driving surface and extend the life of the bridge by several decades.
The funding for the work is being covered by State Trunk Highway funding and MnDOT bridge preservation dollars.
The work also will result in the repair of the Mississippi River Boulevard/Shepard Road and Edgcumbe Road bridge decks; the replacement of the Hwy 5 bridge joints and approach panels; the repair of the Hwy 5 roadway between the Mississippi River and Munster Avenue, replacement of guardrails and medians and improvement to drainage systems.
The Hwy 5 bridge carries 56,000 vehicles daily. Last year saw the repair of the eastbound section of Hwy 5 and the pouring of a new deck as the entire eastbound section was closed to traffic. The bridge also is important for pedestrians and bicyclists — data from May of 2015 shows that an average of 132 pedestrians and bicyclists cross it daily, with higher volumes on weekend days. The Hwy 5 bridge is a critical river crossing that connects popular trails along Mississippi River Boulevard and Shepard Road in St. Paul to trails at Fort Snelling State Park.
“It's one of a handful of river crossings that we have in the St. Paul East Metro area,” said Eric Embacher, MnDOT's resident engineer, “and there is an airport nearby that has a lot of traffic connected to it. The planning for the project started a few years ago. It was originally going to be a design-build project and was later changed to a design-bid-build one. The deck, overall, has functioned well and met the needs of the roadway.
“We're doing some reinforcing and adding stiffeners and other upgrades on the steel, as well as the piers,” he added. “The lighting and rail systems are being retained and the aesthetics of the bridge will not change. The bridge is a fixture of the area and its design fits in with the river bluff area and nearby Fort Snelling. It is important to maintain that historical look.”
The bridge deck that is being replaced was installed in 1986 by Lunda. The deck consisted of a 7-in. (12.7 cm) reinforced structural deck topped by a 2-in. (5 cm) low slump concrete wearing course, which has been the standard since 1979 for bridge routes carrying over 2,000 vehicles per-day.
“Structural decks contain both a top and a bottom mat of steel reinforcing, where each mat is comprised of longitudinal and transverse reinforcement,” said Paul Pilarski, MnDOT regional bridge engineer. “From the period of around 1977 to 1987, MnDOT trunk highway bridges used epoxy coated top reinforcing and uncoated bottom reinforcement. MnDOT switched to all epoxy coated reinforcing in 1987, one year after the bridge was re-decked.
“It has been observed that there is accelerated corrosion of reinforcing where there is such a difference between reinforcing mats,” he said. “The uncoated bottom reinforcement on the Highway 5 bridge showed the same accelerated deterioration, as has been observed elsewhere. The bottom of the deck was corroding at an accelerated rate, resulting in concrete spalling which poses a risk to the public underneath. Normally a bridge deck will yield a 40 to 50 year life with heavier volume bridges, as well as heavier salted bridges, being at the shorter end of that timeframe. This bridge deck lasted about 30 years before it was deemed prudent to re-deck based on level of deterioration. The bridge deck durability was therefore below expectations, but consistent with other bridges of a similar composition, flat profile for drainage and high levels of vehicular usage.”
MnDOT considered placing an epoxy chip seal on this structure five years prior to the project.
“This is a 3/8-in. thick, two-left application of epoxy and rock that largely prevents ingress of new moisture and chlorides that would deteriorate the deck,” said Pilarski. “However, within two years of delivery it was observed that the treatment would be ineffective based on the level of deterioration. The bridge deck reinforcement was already corroding too quickly. If an epoxy chip seal would have been placed, it would have cost around 20 percent of what the current bridge re-deck is costing, but yield a life extension of less than 10 years. For this reason, the greater investment in, and durability of, a bridge re-deck was selected.
“When the investment to a re-deck was selected, it represented a large demand for funding,” he said. “MnDOT looked to salvage any elements which held remaining service life — like the bridge railings, and reinstall them rather than fabricate new railing. When salvaging these elements, a new paint coating system was installed to further prolong their life. As far as innovative materials, first is the concrete we use in the bridge deck itself. Today's bridges are constructed with high performance concrete, which means that the concrete deck surfaces have much higher resistance to chloride penetration, improved freeze-thaw durability and less cracking.
“The bearings upon which the steel girders sit are being replaced for the first time since the bridge was originally built,” he said. “The former bearings, which were solid steel 'rocker' bearings, were prone to pack rust. These are being replaced with disc bearings, which are essentially a neoprene pad that will not corrode, and also has a low friction sliding surface so the bridge can expand in the summer and contract in the winter without high stresses being imparted to the steel girders.”
Pilarski pointed out that MnDOT bridge preservation dollars are being “stretched thin given the high inventory of existing bridges that are showing their age. The bridge preservation and maintenance budget has not seen minimal increases despite the exponential growth in number of bridges to maintain in the inventory. For this reason, investment into lighting and aesthetic improvements besides painting were not pursued. Paint serves as a preservative for the lighting, the steel railing and the girders.”
When the major work resumes in April, the sidewalk on the westbound side of the Hwy 5 bridge will close in early spring 2016 through November while crews reconstruct the deck of the westbound bridge and repair the concrete roadway of Hwy 5. This will result in pedestrians and bicyclists being detoured around the closure due to limited space on the eastbound side of the bridge, which will be used to maintain one lane of traffic in each direction.
The work is affecting all and motorists are not exempt from the demands of the upcoming construction, which will result in both directions of Hwy 5 being placed on the eastbound lanes of the bridge.
“One of the reasons we're not allowing barges in the river is that we need to have all the work done from the base to the top — from up above rather than setting up down below,” said Embacher. “We have the closures in place to do a couple of deck pours and form the deck itself, so the contractor has room to set up alongside the deck. We're also allowing some overnight closures for a few hours for material delivery. Access to the project is one of the challenges, especially as they can't work from the river itself. It is about 80 feet from the river to the bridge, so it's a long reach to set down below and have a crane working that high.”
Most of the construction work is being by day shifts — some extended, with some night shifts expected for the pouring of the bridge deck.
“We anticipate some traffic impact and back up,” said Embacher, “but last year in the first stage of the work, it wasn't as bad as expected or could have been. We're looking ahead to address potential issues so that we're not causing problems.”
The first phase of the work saw Lunda crews repair the concrete roadway. Parts of the roadway were patched up, while larger sections were removed and replaced. Closing off the eastbound side allowed Lunda crews to work at multiple sites.
Embacher said that typical repairs to concrete roads have a 20-year lifespan. MnDOT's Materials Office worked hard to come up with better formulas for the concrete that is used and for this project. Air entrained concrete better withstands the freeze-thaw periods. MnDOT checks the conditions of its roads and major cracks or potholes are repaired rapidly.
Inspections during the eastbound lane work found the road base and sub-grade levels to be in good shape.
“We didn't have to do anything beyond the concrete surface,” said Embacher. “We work with our contractors in a partnership approach and if anything is encountered by us or the contractor, we evaluate the situation and address it.”
The second phase of the project starts in April. The highway overpasses will likely be dealt with in late May or early June, and once started on, have to be completed in 60 days.
The key work is the new bridge deck and measures are being taken by Lunda to prevent debris from falling into the river in order to not impact the environment, particularly fish spawning areas and local species of mussels.
“Lunda is using a false deck under the beams that run from the west abutments to pier 3 on the east side of the river,” said Embacher. “This ensured that none of the concrete from the deck removal fell into the river. They are cutting out slabs and lifting them out. Over the beam flanges they are doing some chipping to remove the concrete. This reduces the amount of debris and the rest of it comes off in one big chunk because they are cutting the deck panels out.”
The challenges encountered last year included scoping repairs to steel superstructure in advance of removing the concrete deck, and having the steel repair materials fabricated and ready for installation when the deck is removed.
“The construction schedule often assumes there will be minimal surprises during construction, and all the repairs are documented in advance in the plans,” said Pilarski. “When dealing with an existing 50-year old steel superstructure, there are obviously locations of corrosion and deterioration that will require repair or replacement. The bridge planning phase reviewed all available inspection data, but it is difficult to fully understand the deterioration levels hidden by the existing bridge deck.
“There was concern that there may be deteriorated portions of the top flange that would result in project delays to repair properly,” he said. “Areas of known deterioration involved the floor beams and bearings under expansion joint locations. These represented a high risk to perform localized repairs, which would require on-site assessment during construction and delayed fabrication. For this reason, floor beams with known deterioration were outright selected for replacement and prefabrication rather than risk potentially iterative investigation and strengthening.
“Stiffeners on the main girder were also known to have varying level of deterioration,” he said. “With the high number of stiffeners, the contract was let with a limited quantity of stiffener repairs. Stiffeners were assessed for replacement using the contractor's work platform for close-up inspection. The resultant quantity selected for replacement was very close to the contract quantity and repairs proceeded smoothly. All of these steel repairs met expectations. The engineering for potential repairs, prefabrication, and cost encumbrance as a preemptive strategy for unknown conditions was one of the hidden successes of this project and MnDOT planning.”
Embacher stressed that another area of successful MnDOT planning was the advanced letting of long lead time items such as the bridge modular expansion joints.
“These items can take up to six months to fabricate,” he said. “If the materials are fabricated in an advance contract, as was performed here and provided to the re-deck contractor, it represents a reduced project risk to the owner and improvement in bid risk by the contractor.”
Lunda will have about six to 10 workers on-site, along with 10 to 20 from the subcontractors. The subcontractors include: Arnt Construction for grading and drainage, Neo Solutions for electrical, PCI Roads for concrete pavement and barrier, Rainbow Inc. for surface finish and paint systems, Safety Signs for traffic control, Sowles Co. for rebar and structural steel, and Terra Services for turf establishment.
When all is done, Lunda will have removed 4,000 tons (3,628 t) of concrete and 210 tons (190 t) of rebar. MnDOT encourages recycling to reduce the amount of material going into landfills, and points out that a lot of the concrete is re-used as material for road base. Lunda expects to bring in 3,000 cu. yds. (2,293 cu m) of concrete and 624,000 lbs. (283,041 cu m) of rebar.
In terms of equipment and vehicles for the road work, Lunda used three dozers, four backhoes, and 10 trucks.
Embacher said the project is proceeding as expected and is similar to many projects that MnDOT embarks upon.
“We work with similar contractors and anything we can do from a partnering perspective or to be pro-active” he said, “we do to mitigate issues. On this project both parties are working well together to make sure that we're building a quality project that we can both be proud of.”
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