These are notes that I am writing to help me learn our industrial history. They are my best understanding, but that does not mean they are a correct understanding.
Tuesday, January 1, 2019
Broadway Bridges over Arkansas River in Little Rock, AR
This crossing had three generations of arch designs. The 1923 bridge originally had five spans of open-spandrel concrete arches.
Bridge Hunter
In 1974, the US Army Corps of Engineers replaced two of the concrete arches with one steel arch as part of the McClellan-Kerr navigation system project. [CultureVulture]
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Bridges Now and Then posted "A postcard postmarked Oct. 4, 1948, shows the Broadway Bridge as it appeared before renovations added an arch above the deck in 1974." (Arkansas Democrat Gazette)
In 2016, the 1923+1974 bridge was removed and replaced with two tied-arch spans. The two arch members in a span slant towards each other, but they don't touch. Even though they don't actually touch each other, I found confirmation that the design is considered a basket-handle arch. [FirstSteel]
After making cuts in the steel members to weaken the bridge, they set off charges to cut through other steel members. But the bridge did not fall! Please read the arkTimes article for a pleasant (no popups) description of how they added more lines and tugs and finally pulled it over 5 hours into their 24-hour window of being able to stop river traffic. Below you can see black spots where some of the explosives were used. Someone in a man-bucket inspected all of the spots and confirmed the explosives went off and cut the members. So the arch stood after the explosions as a testament of the intrinsic strength of that shape.
Arkansas Highway and Transportation Department from arkTimes
(new window) I noticed that they had been building the new piers while they were taking down the old bridge.
Arkansas Highway and Transportation Department from arkTimes
Comment on arkTimes by Arbiter of All Things AOAT: "Story aint over. Looks like the steel remain mostly connected. That cannot be lifted and placed on a barge. They are going to have to send divers into the murky Big Arkie and cut that steel and that is going to be a slow and dangerous process. that's just my guess from lookin at this video. I am talking days if not weeks to clear the channel."
David Hobart posted 1st of 2 arches. Still needing suspension cables and will be ready to float onto piers.
The 3D Satellite image is old enough that it still shows the 1923+1974 bridge. But you can see barges on the north shore preparing for the new construction. The following street views are new enough to show the new bridge, but old enough that you can still see the barges with cranes and the yellow scaffolding used to float the arches into place.
Massman constructed the $100MM replacement bridge for the existing Broadway Bridge, carrying US Highway 70, in downtown Little Rock, Arkansas, for the Arkansas Highway and Transportation Department. The new bridge is a double basket network tied arch, constructed on the same alignment as the existing bridge, supported by three bents over the Arkansas River. To minimize disruption to the travelling public, we executed an innovative plan to install the new bridge substructure underneath the existing bridge while it was under traffic; demolish the old bridge and complete construction of the new bridge in only 180 days.
To meet this contract deadline, Massman installed the three bent main span foundations prior to closing the corridor of the existing bridge. This work consisted of constructing 24 each 8-foot 6-inch diameter drilled shafts with 9-foot diameter permanent casings. The shafts were drilled 65 feet into the rock on the floor of the Arkansas River. The project also included 26,000 square feet of retaining walls with 30,000 cubic yards of fill material. The structure contains 25,000 cubic yards of concrete and 13.5 million pounds of structural steel. Prior to the 180-day closure, two tied arches were assembled downstream of the bridge on falsework mounted on barges. Once assembled, the arches were floated into position in the river and set into their location.
Project Awards:
2020 American Institute of Steel Construction (AISC) Prize Bridge Award - Major Span Class
2018 AGC of Missouri Keystone Award - Transportation & Infrastructure Project $25 Million or More
2017 American Association of State Highway and Transportation Officials (AASHTO) - America's Transportation Awards Finalist
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