|Highways, Byways, And Bridge Photography
I-35W Bridge Construction
Views Of The New I-35W Bridge Project
At The Halfway Point — May, 2008
The busy Interstate I-35W bridge over the Mississippi River in downtown
Minneapolis, Minnesota, collapsed at the peak of rush hour on Wednesday,
August 1, 2007. Once the rescue operation was completed and the site
was cleaned up, MN-DOT was anxious to get a new bridge built. The Flatiron
company from Denver, Colorado, submitted the highest bid, and suggested
a project plan that would take the longest. They did, however, score the
highest on the technical review of the bid responses, and there was
concern that the other bidders would not be able to meet their proposed
timelines. As a result, Flatiron was selected to build the new bridge.
They accepted what sounds like a nearly impossible project, to build
a modern interstate highway bridge in a cramped urban location in the
flight path to a major airport over a river that supported barge traffic,
and do it within a year.
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Flatiron has risen to the challenge. In May of 2008, 6 months into
construction, they announced that they were more than 50% completed.
In fact, they stated that they intended to be completed 3 months early in
order to capture the maximum amount of bonus money. The Republican
leadership became especially excited about this prospect since the
RNC convention will be held in Saint Paul the first week of September,
and a completed I-35W bridge would be a real feather in their cap.
This page is look at the construction project as of May 24, 2008, just
after the halfway point. This morning was remarkable in that it was
one of the only sunny weekend days since the bridge construction started.
It was also the day before the first main span segment would be erected.
Note that these photos had to be shot blindly over a very tall chain link
fence, and it was extremely windy over the river. That resulted in some
shots being a bit tilted, and not being as sharp as they could have been.
The photo above is an overview shot of the river crossing project site.
The approach spans are nearly complete, and the piers are complete. The
gap over the river is still about 500 feet. The photo below shows the
work on the south approach to the new bridge. The old highway was a
combination of steel girder bridge and earth embankment. That embankment
is being lowered as much as 20 feet, and is being extended to reduce the
overall length of the bridge. The new bridge will be about 700 feet
The photo above shows some of the heavy equipment and gives an overview of
the job site on the south end of the bridge. The University math research
building is behind the dirt pile. The photo below is an example of one of
the signs erected by MN-DOT to explain the construction project. The site
is well marked, and guides are available on Saturdays to give tours from
the 10th Avenue Bridge. The guides are retired MN-DOT staff. They do an
excellent public service, and the Saturday tours are well attended.
The photo above shows a tunnel that was included in the project for a future
regional trail to be developed along the river at the top of the bluffs.
While there is no budget for such a trail, the opportunity to build the
tunnel added little additional cost to the project. Workers are currently
putting in utilities and lights in the tunnel. The Red Cross Building is
located one block behind the tunnel.
The photo below is a closer shot of the overall project at the river.
Both photos show a number of white vehicles purchased by Flatiron for the
project. This caused a small media upset when it was learned that Flatiron
purchased the vehicles out of state. Some citizens of the state felt
that Flatiron should have purchased the vehicles locally where possible.
The photo above is the first span of the main river crossing on the south
end of the bridge. This span is being built using the cast-in-place
method. This process involves building an extensive network of falsework
under the bridge to hold up the pieces while it is being built. Workers
then build forms out of plywood. Rebar is assembled inside of the forms.
Concrete is then pumped into the forms. Once the concrete has cured, the
forms and falsework is removed. What remains is a self-supporting concrete
bridge span. The photo below is a close-up view of the falsework and
forms above the main bridge piers. Notice how tall the bridge beams will
be compared with the size of the forklift on top of the structure. The
building in the background is the University of Minnesota steam plant.
The photo above shows the end of the cast-in-place beams and falsework.
We can see that the first two beams are finished by the white concrete
sticking out where the forms have been removed at the end of the beams.
Workers are setting up jacks in front of the beams. Those jacks will
support the first two main bridge segments that will be lifted in place
on May 25, 2008. The background shows a great view of the Lower Saint Anthony
Falls Lock & Dam, the Stone Arch Bridge, Mill Ruins Park, and the
buildings that remain from the old milling district.
The photo below shows the Big Ben crane, a ringer style boom crane built
by Manitowoc Corporation in Manitowoc, Wisconsin. The ringer attachment
allows the crane to handle much heavier loads, up to 600 tons in this
case. The ring supports the crane boom in the front, and the large stack
of counterweights in the back. A similar blue crane is located in a
staging area about a half mile down stream. The blue crane is nicknamed
Big Bohemian due to its location on Bohemian Flats along the river.
The plan for building the center span is simple. Bridge segments are being
cast in a casting yard next to the Metrodome. Segments are loaded onto
a truck that has a zillion wheels, and they are transported down to Bohemian
Flats. The big blue crane lifts them onto a barge. The barge is pushed
to the construction site, where the big red crane lifts each segment into
position. Cables are attached to the segments to pull them tight against
the segments that are already in place. They pull the cables so tight that
the segments essentially act like one huge beam. When all the segments are
put in place, they will hold themselves up mechanically.
The photo above is a closer photo of the north end of the main span. Like
the south end, it is being cast in place on a huge falsework platform. While
the south end uses a large yellow tower crane typical of skyscraper projects,
the north end has two large Manitowoc crawler cranes. Each span also has
a small tower crane segment topped with a concrete pumper. Note that the
bottom of the piers are sitting on a concrete platform at the edge of the
river. There is a storm water outlet below one of the piers. This is
yet another obstacle that had to be worked around when building in a crowded
The photo below is a close up of the falsework and forms. The photo was
shot through the chain link fence, resulting in the white shadows. Notice
how large the structure is in comparison to the size of the workers. Also
notice the large white barrels sitting on the scaffolding. These hold
cooling water for the concrete. Concrete undergoes a chemical reaction
when it cures, which gives off heat. In order to maintain the desired
strength levels, the concrete cannot be above a certain temperature.
Crews maintain the correct temperatures by running cold water in pipes
through and along the surface of the concrete structure. On this
particular day, the temperatures were running on the high side of normal,
so workers put dry ice into the water tanks to make the water colder. You
can see the dry ice vapors coming out of the tank on the right.
The photo above is the north end of the bridge showing the concrete
finishing machine that will be used to pour concrete on the deck. Even
though the beams are not poured yet, work is in high gear building the
rebar for the deck. This is an example of the parallelism being used
to speed up construction. In most cases, a contractor would conserve
materials and build repeatable processes by doing one cast-in-place
span at a time, repeating the 4 builds in sequence. On this project, time
is the key driver, so all of these items are done at the same time.
The photo below shows the north end of the bridge with downtown
Minneapolis in the background. The row of green material just above
the plastic is the rebar for the highway deck. Notice the large number of
workers on the structure. In all, there are 600 workers on the project,
running in two 12-hour shifts each day, 7 days a week.
The final span on the north end has yet to be started. The area is
being used for staging of the construction of the main spans. This
location used to be a major rail yard. That yard was cut back in
size in the 1990s, and part of it was developed for housing. The
last major rail shippers in the area were Pillsbury and the University
of Minnesota steam plant. The long term plan for this area is to
remove the rail and establish a new parkway along the river and
past the north side of the U of M campus.
The photo below is the bridge span over SE 2nd Ave. This area was
crossed by the old bridge, but since the new bridge is much shorter,
a stand-alone bridge was needed.
The photo above is the last photo of our tour crossing the 10th Avenue
Bridge from south to north. This photo is looking at the area between
SE 2nd Ave and University Ave (the overpass bridge). This area is being
lowered up to 28 feet. That requires excavation of the old highway
approach as well as building retaining walls. A small daycare center
had to be torn down near where the yellow Grove crane is parked.
The photo below is a view of the casting yard that was set up on the
old highway between the old bridge and Washington Avenue. In this casting
yard, they set up forms to build the individual segments that make up the
main channel span of the new bridge. The segments are cast
under controlled conditions, and then trucked to the job site and erected
using large cranes. There is a nice view of downtown and the Metrodome
in the background. Also notice that a concrete pumper is at work near the
right side of the photo. Finally, notice the series of white objects
under and to the left of the concrete pumper. Those are completed bridge
segments that are ready to be transported to the job site.
The photo above is the north section of the casting yard. A bridge
builder would normally use one set of casting forms for a project, and
use them a number of times. In this case, time is more important than
money, so the goal is to cast the segments quickly. Notice the white
H-frame machine behind the forms just above the
dust cloud. That is a Shuttlelift model SL300 gantry crane. It is used
to move the segments out of the forms and to load the segments onto the
transporter truck. Shuttlelift machines are built in Sturgeon Bay,
The photo below is an overview of the area north of Washington Avenue
and south of the river crossing. The cranes supporting the bridge project
can be seen in the distance. The activity taking place is that the roadway
is being broken up and the pavement is being removed for recycling. This
roadway will be lowered up to 20 feet, so a new grade will be required,
along with new pavement.