Wednesday, September 13, 2017

Road Bridges over St. Croix River near Stillwater, MN

1931 old lift bridge: (Bridge HunterHistoric BridgesJohn A. WeeksSatellite, 177+ photos)
2017 extradosed bridge: (John A. Weeks-newSatellite, at the time I looked, the image had just a couple of construction barges anchored in the middle of the river)
Satellite

While researching the CN/SOO/Wisconsin railroad bridge, I discovered they are building a new 4-lane bridge for Stillwater, MN. The new bridge includes a trail with overviews. [Background] They plan to preserve the old lift bridge and make it part of a trail system. [Liftbridge]

The truss bridge was built in 1931 and rehabilitated in 1973. The replacement one-mile-long, bluff-to-bluff bridge started in 2013 was scheduled to be done in Fall 2016, but it was almost a year late (Aug 2, 2017). The new bridge does uses post-tensioning with almost 2,000 miles of segment strands. [video] (All of the videos are below in the order that they should be watched.)

John Weeks posted some bridge pictures with extensive comments on the photos.
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The old Stillwater Lift Bridge over the Saint Croix River. This bridge was just recently closed to highway traffic and it will reopen soon as a dedicated pedestrian and bicycle bridge. It will be part of a trail loop that goes over both the new and old bridge that is expected become a regional tourist attraction.

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The new Saint Croix Crossing bridge. A cell phone photo doesn't do it justice. This is the first and only bridge of its type in North America, an extradosed structure. It uses 5 sets of short towers to avoid spoiling the view from the river, whereas a more conventional cable stayed bridge would have had a pair of 500 foot towers that would have been totally out of character along a National Wild and Scenic River.
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Approaching the new Saint Croix Crossing bridge on the ramp leading up to the pedestrian / bicycle deck.

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A view of the bridge deck as seen from one of the bump-out observation decks. What makes this bridge type unique is the angle of the suspension cables. Having the cables go directly from the towers to the bridge deck is becoming an increasingly popular design (where there is no catenary cable strung between the towers), a type known as a cable stayed bridge. However, on this bridge, the cables are at a shallow angle where more of their force is pulling towards the bridge tower than is lifting the bridge deck. The bridge stays up not because the cables are holding up the deck, but because the cables are pulling the deck segments towards the towers making them a really strong beam. This is known as an extradosed design. I don't know where the word comes from, but it is the first of its type in North America.

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Historical marker on the Wisconsin side of the Saint Croix Crossing bridge. I have followed the river all the way north to its source and the swamp where one side drains to the Gulf of Mexico via the Saint Croix and Mississippi, and the other side of the swamp drains into Lake Superior and the Saint Lawrence Seaway.

At one time, it was proposed to build a canal through northern Wisconsin to connect ships from the Saint Lawrence to the Mississippi, but that would have totally destroyed the river ecosystem. Later, it was proposed to build a massive power dam that would have flooded a large portion of northwestern Wisconsin. A young senator from Minnesota named Walter Mondale took up the fight leading to the establishment of the Wild & Scenic River Act to forever preserve the Saint Croix River (and other selected rivers across the US) for future generations.
MNDOT Banner
Photo from Gallery from MNDOT
Photos and information about its construction
The bridge itself will be only the second extradosed bridge to be built in the United States. An extradosed bridge is similar to a cable stayed bridge, but with a major difference. In a cable stayed bridge, the cables hold up the deck segments. That requires tall towers and a steep angle for the cables. An extradosed bridge uses the shorter towers to support the deck segments near the tower. The relatively shallow angle of the cables means that they mostly pull the deck segments together rather than holding them up. The result is that the segments are held tightly together, so they essentially perform as single beams. The extradosed style is more expensive than a beam bridge, yet cheaper than a cable stayed bridge. It requires fewer pylons than a beam bridge, but more than a cable stayed bridge. [John A. Weeks-new]
John also explains that environmentalists fought a new bridge for decades because the river is designated as a National Scenic Riverway. It took an act of Congress in 2012 to allow the new bridge to be built without having to destroy the historical lift bridge.


Jeremy Rawlings posted
888 Ringer with 250ft of main boom setting precast segments for the St Croix River Crossing between Stillwater, MN and Houlton, WI. Summer of 2016.
Mike Weaver Looks like a 14000 in the background.Jeremy Rawlings Yep. While I was on this job we had two 888 ringers, a 2250, a 888 crawler, that 14000 and an MLC 165 and a Link Belt crawler. All of them were on barges except one of the ringers which was on the Wisconsin shoreline. There were a couple American friction rigs, a couple Link Belt 110s and a 16000 along with a few pickers on land.

Jeremy comments on his posting
Here’s the 14000 boomed down to get it under the bridge.
 It did list the barge with it boomed down that far but list of the barge is exaggerated a bit because they were moving it. You can see the tugboat on the right side of the barge and there was another one behind the crane to push.

Jeremy comments on his posting
Here’s a picture where you can really see the list of the barge while being pushed by the tugboat and you can see both tugboats.
RoadBridges
"Construction operations needed to be contained within a 400-ft zone in the river, and the National Park Service imposed strict timelines on barges transporting the precast segments from the casting yard through the locks, allowing only 72 hours per run, limiting the exposure of these vessels to the invasive zebra mussel. If any barge exceeded that time limit, it would have to go through a complete inspection and wash-down to prevent the mussels from passing between the Mississippi and St. Croix Rivers."

Bill Pohlmann posted
One of the little Japanese models [Kobelco] working on the historic Stillwater, MN lift bridge. Its replacement opened a few years ago and it's being converted to a bike and pedestrian bridge.
Robert Thiry love that ‘no parking’ sign.
Bill Pohlmann Yeah, the rivers are kind of high around here!
(source of videos: bottom of stcroixcrossing) If you want an just a quick overview, skip to the last two videos which are time lapse videos.

If this part of the river had a rapids, then multiple, short towers would be relatively cheap because the bedrock would be close to the surface. But this video indicates the towers are rather expensive because the pier caissons go down as far as 140 feet.
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A different time lapse:
(new window) from MNDOT



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