Rehabilitating a high volume, critical bridge span over a busy river channel under traffic conditions while maintaining the graceful arch design features of this historic 1920s spandrel arch bridge is a construction challenge some contractors might prefer to avoid.
However, this is the challenge workers for Kraemer and Sons, of Plain, WI, have faced for a year as they near the mid point of construction to rehabilitate the historic Ford Bridge spanning the Mississippi River between the cities of St. Paul and Minneapolis. This bridge provides a critical link between the upscale neighborhoods of Highland Park and its trendy Highland Village shopping center in St. Paul, and the popular and busy Minnehaha Park region and neighborhood in Minneapolis. It carries more than 16,000 vehicles per day.
Kraemer and Sons is the general contractor for the project. Designers for the rehab project are H.D.R. of Omaha, NE, and Short, Elliot, and Hendrickson (SEH) of St. Paul, MN. The counties of Ramsey and Hennepin own the bridge.
Eventually, five contractors will work on the project. This work includes demolition and reconstruction of the existing bridge deck and substructure, updated lighting, approach restoration and a new ornamental handrail system.
J & L Steel Erectors, of Maple Grove, MN, is installing the reinforcing and post tensioning system; Rainbow Inc., Minneapolis, MN, is performing surface repairs of the remaining substructure and the special surface finish; Collins Electric, St. Paul, MN has the bridge navigation lighting contract, and Progressive Contractors Inc., St. Michael, MN, will be installing the high-performance micro-silica overlay.
The graceful arches of the 76-year-old bridge complement the steep and scenic bluffs that loom above the river’s edge. It is a reinforced concrete, open-spandrel, two- rib, continuous arch bridge with an overall structure length of 1,524 ft. (461 m). The out-deck width is 64.7 ft. (20 m) carrying a 50-ft. (15 m) roadway and two, 6 ft. (2 m) sidewalks.
The three main arches each has two five-centered ribs with a 300-ft. (91 m) span and is flanked by single arch spans of 139 ft. (42 m) each. In all the arch spans, twin spandrel columns spaced uniformly apart support the floor beams.
All piers, except for a few of the smaller approach piers, sit on solid sandstone. Four cylindrical concrete caissons carried to rock about 70 ft. (21 m) below river level support the two middle river piers. Crews built the original bridge using a 15-ton (13.5 t) cable way span 1,900 ft. (576 m) long and mobile timber towers 135 ft. (41 m) high.
The $19-million rehab includes construction of a new deck and cantilever floor beam brackets with post-tensioned tendons to carry the widening of the deck. The new 56-ft. (17 m) roadway will include two 6-ft. (2 m) shoulders and four 11-ft. (3.3 m) lanes. Two 10-ft. (3 m) sidewalks will be added for a total deck width of 83.5 ft. (25 m).
An estimated total of 2,871 cu. yds. (2,195 cu m) of structural concrete will be poured, 2.2 million lbs. (1.02 million kg) of rebar will be placed, and 101,668 sq. ft. (9,445 sq m) of concrete will be removed.
The south side of the bridge offers an overlook of the lock and dam activities of the Ford dam. The upriver, north side of the bridge offers a panoramic view of the Mississippi River and its 100-ft. (30 m) tree-covered bluffs that loom above its banks.
Construction is approximately two months ahead of schedule despite some lost time in late winter when the fickle Minnesota climate changed suddenly from a mild winter to a cold, snowy one in February and March.
“We were getting into quite a bit of snowfall, some high winds and really cold temperatures,” Mark Olsen, Kraemer and Sons construction superintendent said of winter’s appearance late in the season.
Yet, Olsen’s crews quickly made up for the few days of lost time under the accelerated efforts of Kraemer’s superintendent Tom Duffy who has moved the project almost two months ahead of schedule, Olsen said.
According to Chuck Gonderinger, project designer with HDR, an inspection in 1997 by state engineers revealed major expansion joint failures and column deterioration.
“The failure of the expansion joints allowed water tainted with deicing chemicals to drain from the deck to the floor beams and spandrel columns; causing corrosion of the reinforcing steel,” Gonderinger explained. “This, in turn, led to delamination and spalling of some of the concrete,” Gonderinger added.
An extra inspection revealed even greater deterioration of the columns and floor beams at the expansion joint locations. With the deck in such serious condition, Ramsey and Hennepin Counties decided the entire bridge deck needed replacing along with floor beams and columns at the expansion joints.
Olsen added that closing the bridge to traffic would probably have shaved a year off of the two-and-a-half year construction schedule, but it was not a practical option for Ramsey and Hennepin County officials.
According to Jim Tolaas, project engineer for Ramsey County, the economic impact to users, businesses and the community at large was compared, both for construction under a full-closure scenario and construction under traffic. User time, vehicle operation costs, reduced business activity, tax losses and other factors were analyzed. The data clearly showed the overall impact, cost to users and businesses far exceeded the higher cost of construction under traffic, Tolaas said.
“While construction of this magnitude can’t help but disrupt daily activities in the surrounding area,” Tolaas commented, “Feedback from residents has been positive, with general appreciation for our efforts to minimize impacts in the community.”
While closing the bridge entirely would have greatly reduced construction time, working under traffic conditions is more cumbersome than challenging, Olsen said.
“It limits our deck space for storing materials and equipment,” Olsen explained. Further, “equipment fueling is done from the traffic side and we also have material deliveries such as rebar and forms done from the live traffic side that we just fly off from the trucks.”
Olsen describes this project as one big learning curve. Taking the rebar off trucks on the top side of the bridge is one example of shaving off labor hours.
It was originally done from the river below. One hundred fifty thousand lbs. (68,182 kg) of rebar came from the barge below and was hoisted top side by an American 9299 crane. However, this required iron workers to go down to the barge and sort through the entire shipment of rebar.
“It was too time consuming,” Olsen said.
After meeting with rebar suppliers from Ambassador Steel, Menomonie, WI, Olsen and their reps devised a top-side delivery system from trucks.
“Due to limited working space, we broke rebar deliveries down into very small packages and releases, spread the deliveries out and picked anywhere from 10,000 to 20,000 pounds of steel off the truck,” Olsen said. “It greatly reduced the labor time involved from sorting and hoisting the rebar from the barge.”
Depending on crane availability, rebar deliveries can be off-loaded road side with either of two cranes top-side, or with the 9299 on the river barge anchored below making blind picks off the deck, Olsen explained.
Kraemer and Sons used its own American HC80 and a 35-ton (31.5 t) Terex Hydro owned by JCR Crane Inc., Baytown, TX, for the top-side delivery picks.
Maintaining the historic architectural elements of a bridge noted for its structural beauty of long, graceful arches is an ongoing learning curve element and challenge for the crews who recreate the forms and deliver them to their place on the bridge, Olsen said.
“Architecturally, we’re retaining the integrity of the bridge to include all its design elements that were developed back in the 1920s,” Olsen explained.
Some of these design elements include the long, curved belly of the cantilever brackets, maintaining the square spandrel columns, and replicating the shape of the capital pieces. And more apparent from the topside of the bridge are the posts for the ornamental hand railing and the signature blocks at the end of the bridge.
The American 9299 is the biggest piece of equipment on the site.
“When you get on a project like this with limited deck space and some of the large removal areas that we have, bigger always seems to be better. Our workhorse is the American 9299. He’s the most mobile, the heaviest worker that does our biggest picks,” Olsen said of the 165- ton (148.5 t) crane with a 240 -ft. (73 m) boom length.
One of the more unique pieces of equipment used on the bridge is the UP90 made by Stanley/LaBounty of Two Harbors, MN.
“It has been very useful in removing the 55-foot columns which could not be reached using conventional concrete breaking equipment,” Olsen explained.
The UP90 consists of a set of mammoth jaws that basically chew up concrete. The column caps and top 5 ft. (1.5 m) of columns were removed with the UP 90 attached to a Liebherr 954 excavator.
“One hundred feet of hydraulic hoses were fabricated to connect the Liebherr 954 to the UP 90 which provided the hydraulics to operate the jaws. The crane operator would position the processor over the column and advise the excavator operator when to activate the jaws,” Olsen explained. The balance of the columns were removed with the UP90 attachment cable hung from the 9299.
Olsen’s crews recently completed the first construction phase. The westbound deck has been completed. Crews recently switched two-way traffic to the new, much wider deck and are now beginning demolition of the eastbound deck.
The Ford Bridge is significant as one of the largest, reinforced concrete bridges built in Minnesota. Notable features include the sinking of the caissons and construction of sheet pile cofferdams to rock 70 ft. (21 m) below the river surface. The state historical society recognized the 1,900-ft. cableway and large concrete plant and delivery system as an innovative construction technique.