For the nearly 80,000 motorists speeding across the I35E Bridge over the Mississippi River as they head into or out of St. Paul, MN, the only signs of construction activity are a couple of cranes towering slightly above the bridge deck.
However, below the deck, construction crews, during the last year, have constructed five new bridge piers and hoisted into place the first three out of five lines of steel girders to carry the northbound lanes of a completely new bridge.
Eventually, the new bridge, designed to current federal standards, will carry two through-lanes of traffic in each direction. A third auxiliary lane in each direction will make it safer for traffic to merge onto the traffic lanes. The bridge deck will include an 11-ft. 10-in. (3.6 m) bikepath; a feature not on the current bridge.
The end result will be a bridge that is the same length as the 1,406 ft. 4 in. (42 m) current bridge but twice as wide at 137 ft. 3 in. (41.8 m).
With a projected ADT of nearly 126,000 vehicles in 2021, it will have a capacity that is 40,000 vehicles more than the current ADT that is now crossing the bridge under high speed, dense traffic conditions. And the wonder of it all is that the new construction will all be done with little disturbance to the heavily traveled, existing bridge.
To keep the daily flow of traffic moving with minimal disturbance for motorists, Minnesota Department of Transportation (MnDOT) engineers designed the bridge to include five stages of construction.
During the first stage of construction, which began last October, construction crews pounded pilings and drilled caissons for the five new piers to carry the superstructure and deck of the new bridge. Then they formed the five new bridge piers and poured the concrete during the winter, spring and half of the summer construction season.
Stage two construction started when steel workers began hoisting and connecting the first three lines of steel girders in May. All three lines of girders were in place by late August.
Two lanes of the new northbound deck will be completed, and all northbound traffic, from the existing bridge, will switch to the new deck during the third stage of construction. Also, the existing southbound superstructure will be removed, and the beams for the new southbound superstructure will be placed.
During stage four construction, all traffic will move to the new southbound lanes and the existing northbound superstructure and piers will come down.
Finally, stage five construction will complete the bridge deck for the two through-lanes of northbound traffic.
The bridge is a continuous welded plate girder span. A total of nine steel girders will be placed on five tulip style bridge piers to carry the superstructure. Each girder is made up of 13 separate welded sections. The total construction cost is $22.3 million and is financed from a 90/10 split of federal and state bridge replacement funds.
Ed Kraemer and Sons, of Plain, WI, is the general contractor for the project. High Five Erectors, of Shakope, MN, is the steel erection subcontractor. Shafer Contracting Company, of Shafer, MN, is doing the excavation work. A total of 14 subcontractors are working on the site.
The steel comes from the PDM Steel fabricating plant in Eau Clare, WI. It is trucked to the construction site by Perkins Trucking, of Grand Junction, CO. The company specializes in moving mammoth objects over the road. ABI Trucking is transporting much of the smaller steel beams.
Closing the old bridge and knocking it down to make room for the construction of the new structure was out of the question, said Arlen Ottman, MnDOT chief design engineer of the new bridge.
“There is no suitable detour to route the high volume of traffic we have on the existing bridge,” Ottman noted.
The existing bridge, even though it is only 35 years-old, has outgrown its usefulness, he said.
The ADT of nearly 85,000 vehicles that the bridge now carries now creates back-ups and, at the least, very crowded driving conditions. As a result, the structure also is showing signs of the heavy use.
“The original construction is welded steel plate girder,” Ottman explained. “The welding technology used for that bridge was not as sophisticated as it is today; and cracking is occurring in some of the steel members.”
Further, the existing bridge has no merge lanes and no shoulders for emergency stops. Currently, motorists move immediately into high volume, high speed traffic. The new auxiliary lanes will eliminate this hazard.
Another improvement of the new bridge is its redundancy. If one of the beams fail, the load can be transferred to the remaining steel members of the new structure. The existing bridge is a non-redundant structure, Ottman said.
“It just has two main beams for each roadway. If one of them fails, then they’re both likely going to fail,” Ottman explained.
Construction is progressing well despite pounding, monsoon rains early in the summer construction season.
High water delayed work on the first pier for a couple of weeks. And, the strong, swift river taxed the strength of the two tug boats from Portable Barge Company, Newport, MN, moving the steel from its lay down site on the north river bank to the cranes stationed on floating barges on the south side of the river.
Steve Kaldenbach, Ed Kraemer & Sons construction site superintendent, explained that the two tug boats did not have enough horsepower to handle the swift river as tug operators crossed the river with their mammoth steel loads perpendicular to the current. “At one time we actually had three tugs helping us out moving the structural steel,” Kaldenbach said.
Each of the welded structural steel girders carrying the bridge deck is composed of two, huge 165,000-lb. (74,843 kg), 145-ft. (44.2 m) haunch girder sections, which sit on the two main river piers and 12 smaller sections of varying lengths.
To hoist the haunch girder beams to their positions on the piers, Kraemer and Sons used in tandem a P&H Delta 5250 250-ton (226 t) crane owned by Portable Barge Service and a Link-Belt LS-238H 165-ton (150 t) crane owned by Imperial Crane Services, of Bridgeview, IL.
A Grove 300 crane owned by Armstrong Rigging and Erecting Inc., New Brighton, MN, assisted the Delta and Link-Belt cranes with the hoisting of the straight girders at the south pier.
Along with the high and fast current, building a new bridge while keeping the old bridge open to traffic presented its own set of unique challenges. The five new piers were all formed and poured beneath the old bridge superstructure. As the piers neared their full height, the top of the forms were just inches from the bottom of the old bridge.
Also, steel erection has been done with the river channel remaining open to commercial traffic and recreational boaters. Recreational boaters can cause potential problems for the crane operators and steel workers, Kaldenbach said.
“When we’re up in the air setting steel, we have to watch out for the recreational boaters. They can come through the channel real fast and if they slow down fast, they just plow through the water and make a big wave and that can be pretty detrimental.
“So if your right in the middle of a big pick, a wave could upset the balance especially when you’ve got guys trying to guide two steel pieces together. If you upset the balance of the crane and that piece of steel shakes, you could knock somebody off or put somebody in the pinch point, so it can be pretty disastrous,” he noted.
Each crane has a load cell attached to it so that the operators know how much weight their cranes are lifting into the air. The load cells, combined with the crane operators experience and each crane’s traits help for a smooth, even tandem lift, Kaldenbach said.
In setting the structural steel, the crane operators and iron workers also have to use extreme caution at the bridge deck because they are setting beams within several feet of some of the traffic crossing the in-place bridge.
The local topography and man-made obstacles also challenged the construction. On the south end of the project, the bridge hits a steep bluff with railroad tracks and a bicycle path running beneath the bridge on the only available, narrow, piece of flat ground.
“You just don’t have anyplace to put a crane. That last 150 ft. is kind of like a dead zone. You really can’t get much access to it,” Kaldenbach said.
Complicating matters and making for even tighter working conditions is a high power voltage line just 100 ft. (30 m) downriver and running parallel to the new construction on the east side of the bridge. Consequently, the crane operators had to watch their boom lengths and radiuses when setting the forms and steel.
Ed Kraemer and Sons coordinated its steel lifting activities with the local water patrol and U.S. Coast Guard.
While construction continues on the bridge, Shafer Contracting has been digging, hauling material in and out, and grading the ramps at either end of the bridge. Shafer uses Caterpillar dozers, loaders and graders; Komatsu and John Deere backhoes; and Dynapac, Bomag and Ingersoll-Rand drum rollers.
Crews will soon begin demolition on the southbound portion of the in-place bridge and begin setting the structural steel through the upcoming winter and spring seasons. The bridge is expected to be completed in June 2004.