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The Wisconsin Department of Transportation, or WisDOT, introduces an innovative technology
in bridge-building, called Self-Propelled Modular Transporter, or SPMT. During the summer
of 2013, the bridge at Rawson Avenue in Oak Creek, outside of Milwaukee, was the first
bridge in Wisconsin to be constructed using the SPMT method.
The project was part of the I-94 North-South Freeway Project. The corridor reconstruction
project started in 2009 involving stretches 35 miles between the Mitchell Interchange
in Milwaukee, through Racine and Kenosha Counties to the Illinois state line. It expands the
interstate to four lanes in each direction and redesigns 17 interchanges, reconstructing
the Rawson Avenue Interchange to a tight diamond interchange including new entrance and exit
ramps to and from Interstate-94.
Traffic counts show about 112,000 daily vehicles on I-94 just north of Rawson Avenue, and almost
43,000 daily on the Rawson Avenue bridge. Those statistics prompted efforts to minimize
construction time, and in particular, bridge closure time.
As part of the Federal Highway Administration, or FHWA, "Every Day Counts" initiative, WisDOT
constructed a new bridge on the interchange, via innovative construction methods in the
staging areas both east and west of I-94. The bridge only needed to be closed for about
three weeks, instead of the five or six months for a typical replacement project, because
a new technological method called the Self-Propelled Modular Transporter was the main player in
the project.
In constructing the elements off-site, it gives the workers the opportunity to develop
and build a higher quality product where their focus can be primarily on the work operations
and less on their safety relevant to the traffic in the vicinity.
The SPMT process involves three key steps: Build the new bridge out of the way of traffic.
Close and demolish the old bridge. Move the new bridge into place with the SPMT.
The previous structure, dating back to 1963, was taken down over two 4-night periods in
March and May of 2013. It was demolished and the steel girders removed. Pier substructures
and abutments were also demolished. The new replacement bridge was constructed on-site
using temporary supports called shoring towers on each side of I-94. Also, in early spring
2013, concrete girders and columns and pier caps support structures were pre-cast, and
the internal rebar core was created, framed and poured. Once the bridge decks on either
side of I-94 were constructed, WisDOT proceeded from April through June 2013 with pile driving
and pouring of concrete, done in stages because the second half of the existing bridge needed
to stay in place until the end of May.
Well, I mean anywhere you go in Oak Creek you're seeing construction. We, you know,
we're in the process... multi-year process of revamping the interchange and all the bridge
decks going over our main East-West streets. So it obviously has an impact on our traffic
patterns. But I think the biggest thing that I notice is, it's not a lot of complaints,
it's people saying, you know, "That really looks nice. That bridge deck looks awesome.
I love the metal work that's been done on it. I love how the expansion has eased the
congestion." So, whenever I talk to people about that issue - traffic - I always say
we're in the middle of a long-range plan to make it easier eventually to move around the
city. So, that's the focus I have on it. These are things that have to be done. I'm a freeway
guy, I think we need to always be able to move traffic efficiently and effectively.
So, for me, these are all necessary parts of that end product, which is, at the end
of the day, will be moving people effectively; making it easier to move around in our city,
which helps development, which helps our residents; makes everything a lot smoother.
Pre-cast concrete girders built off-site were brought in and set on the shoring towers,
making a span. Then the concrete bridge decks and sidewalks were cast in place on-site.
Next, the spans located in both the east and west Bridge Staging Areas, or BSAs, were lifted
using a Self-Propelled Modular Transporter heavy lifter to raise the bridge decks, roll
them into place and set them onto the pre-cast columns. Both halves of the bridge were positioned,
weighing about 1,500 tons each for the east and west spans. That's about the equivalent
of more than 40 fully loaded semi-trucks. Placement on the new structure posts took
about twelve hours to complete. Closure pours were made after that.
An SPMT is a motorized multi-axle platform operated through a state-of-the-art computer
controlled system capable of pivoting 360 degrees. The apparatus can lift, carry, and
set very heavy loads of many types. Controlled by a hand-held control panel, the SPMT is
rolled into place at a walking pace and sets and affixes concrete precisely into its final
position onto pre-cast columns and caps.
With the use of the SPMT we were able to put the bridge in place over a 12 to 14-hour period,
versus conventional methods where we would have many lane closures over prolonged periods
of time; interrupting thousands of travelers over that period of time.
The new structure at Rawson Avenue in Oak Creek was rolled into place overnight, beginning
at 10:00 p.m. on June 14, 2013. With other parts of the Rawson Ave. Interchange Reconstruction
taking place, Rawson Avenue reopened to traffic in late June. Exit and entrance ramps to I-94
remained closed to traffic until late fall.
I'm amazed they can do projects that big with so few people in such a short amount of time,
again, minimizing the impact on the city. So, that's been the cool thing for me. When
I found out that each of those decks weighed 3 million tons, or whatever it was. That's
an impressive number; to be able to move that in a span of a few hours - that's an impressive
thing. For that to happen in our city, I think says something. I think it's that we and the
DOT can partner up on projects like this and minimize the impact for our residents. But
also help the state move forward on transportation, which ultimately helps everybody; not only
the residents but the businesses, because you have to move product, and you have to
move people, and it does both of those things. So, however we can make that more efficient,
I'm a big fan of.
The benefits of this technology are to supplement accelerated construction bridge techniques,
which is the nation-wide trend that FHWA is pushing. And I know Wisconsin really wants
to be a part of that. But this technology has the potential to really allow us to build
very complex structures and integrate them into our construction schedules to have drastic
reductions and impacts on the traveling public. And it's very exciting to be able to see what
this technology can do on this Rawson Avenue Project, and to then parlay that into implementing
it on future construction areas and locations. And the overall goal, here, is to build quality
projects and minimize inconveniences to the tax payers and the traveling public. And that's
an exciting thing to be involved in.
I've attended a bunch of meetings with the DOT and local businesses, residents; lots
of communications; email, phone, in person. I have the highest regard for how these types
of situations with major projects like this are handled. I always, as a mayor, I always
use the complaint quota - or quotient - and on this project, specifically Rawson, I have
not gotten - I've gotten very few complaints. Whereas I could get more about our garbage
pick up. This hasn't even come onto the radar. So, that tells me that the DOT is not only
communicating effectively with the local officials and the residents, but they're also talking
to the businesses that are impacted. I see increased signage to help people move around.
I see directionals that move the traffic away from a problem area, in this case, Rawson
Avenue. So those things indicate to me that they went at it the right way. And they made
sure that we were the least impacted by what is a really, really big project in our city.
Yeah, the use of self-propelled modular transporters is not something that can be employed on every
bridge. If this goes very well, and it goes very seamlessly, I know the community and
the traveling public would be probably would be very eager to see every bridge built this
way. And wouldn't we like it to be that way? The fact is, though, that there is a premium
cost that we pay to get these specialized moving equipment in here. It travels around
the country and is only brought in at specific windows. And it's not for every bridge. There
is a lot of technical complexities to be able to build the bridge off-site and wheel it
in and set it down gently in place. So that's a real big reason why the Department and the
Bureau of Structures is utilizing this on the Rawson Avenue interchange. There is a
cost that you pay to bring the mover in. And it needs to be weighed out by the user delays
and the impacts to the traveling public that can be offset by that premium cost. So that's
really why we're trying this out. We want to be comfortable with the technology, and
feel, ah, be better prepared to analyze the best fit scenarios for the types of structures
that we can minimize user delay and not inconvenience the traveling public. So that's what we're
hoping to get out of it: To learn how to apply it to future construction projects.
For more information about bridge structures, visit dot.wisconsin.gov and look under "Projects"
then "Bridges."