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Tue April 29, 2014 - Southeast Edition
Connecting downtown Knoxville, Tenn., with south Knoxville and serving as a gateway to the nearby Great Smoky Mountains National Park, the Henley Street Bridge has been carrying U.S. Route 441 traffic across the Tennessee River since 1931.
In 2011, the deteriorating bridge was dismantled down to its iconic arches, as part of a multi-million dollar rehabilitation project.
“[The Tennessee Department of Transportation’s] bridge engineers determined the bridge was structurally deficient, with deteriorated concrete, deteriorated decks over each of the four main spans and deteriorated floor beams,” said Mark Nagi, community relations officer of Region 1. “The bridge did not meet safety standards and the structure did not meet current minimum seismic requirements.”
Named for Colonel David Henley, a Revolutionary War officer and War Department agent stationed in Knoxville in the 1790s, the 1,793-ft. (547 m) bridge is an open-spandrel arch bridge constructed of reinforced concrete, with six dual-ribbed arches connected by lateral bracing. The deck is made of six concrete girders and is slightly wider than 70 ft. (21.3 m).
After dismissing the first contractor it hired over an argument about the proposed width of the initial bridge, the city of Knoxville rejected a 36-ft.-width (10.9 m) design in favor of a 54-ft.-wide (16.4 m) bridge design submitted by Marsh Engineering Company of Des Moines, Iowa. However, arguments ensued — over materials, size and the choice of construction supervisor. The city chose local engineers, who made numerous modifications to the design.
Almost 80 years later, in 2008 average daily traffic figures were 38,813 vehicles a day, or 14.2 million vehicles per year, Nagi said. The old bridge began showing considerable signs of wear. As an important route, the project rated highly on TDOT’s radar.
Plan of Attack
The major rehabilitation plan called for improvements that include five total lanes of vehicular traffic, two bike lanes and sidewalks and improved lighting.
“Due to the excessive amounts of degradation, TDOT deemed it was necessary to remove and replace the entire deck, sidewalks, railings, girders, floor beams, spandrel columns to the top of the existing concrete arch ribs, upper portions of the abutments and piers, wing walls and roadway approach slabs,” Nagi said. “The main arches and piers are the only salvageable components of the original structure.”
To begin work, Henley Bridge was closed to traffic on Jan. 3, 2011. But before any work on the historic six-span bridge could begin, work required for the detour began in October 2010.
“TDOT began in summer 2010 alerting businesses and local partner of our intended detours,” Nagi said. “The addition of lanes and signals on temporary detour routes was one of the first tasks completed.
Also prior to the commencement of work, Thompson Engineering was called in to perform a construction engineering inspection and assist with community outreach services.
“An extensive community outreach plan was developed that included public service announcements,” Nagi said. “There was significant media coverage as well. A Henley Bridge Community Office was opened near the site to give the public a place to come and answer questions.”
TDOT established a web site for the project (www.tn.gov/henley) and provided live cameras, which “gave the community a way to view the progress of construction,” Nagi said. “We worked with the University of Tennessee to inform the student and faculty population, and informed emergency responders about the detour routes. GPS mapping was used to inform motorists of the closure.”
By the Numbers
Originally budgeted for $24.6 million, Nagi said the revised contract amount at $31 million, to be paid with 80 percent federal funds and 20 percent state funds.
Under general contractor Britton Bridge LLC, Mt. Juliet, Tenn., an average number of 60 to 70 workers per day were tasked with removing and replacing more than 2,400 tons (2,177.3 t) of concrete and more than 175,000 lbs. (79,378 kg) of rebar, most of which was recycled and used in the new bridge deck.
Barges, tugboats, 8 to 10 cranes of various sizes, and assorted equipment were used to help place:
• 958 tons (869 t) of backfill
• 125,410 lbs. (56,885 kg) of structural steel
• 1.2 million lbs. (544,310.8 kg) of epoxy-coated reinforcing steel
• 1.4 million lbs. (635,029 kg) of steel bar reinforcement (bridges)
• pre-cast concrete beams
• concrete railing
• 5,468 cu. yds. (4,180.6 cu m) of Class D concrete for the bridge deck
• 7,063 cu. yds. (5,400 cu m) of Class A concrete for the bridges
Making up for Lost Time
Crews worked 10 to 12-hour shifts Monday through Saturday during the majority of the closure, making up time after a two-week stoppage called by TDOT. The delay was due to the death of two workers, killed in two separate incidents on site, for which Britton Bridge was fined.
Previously undetected deficiencies in the bridge structure also delayed progress and contributed to increased costs. Initially set for completion by June 2013, the project was delayed. Based on added repairs, TDOT moved the projected date to late February 2014 after discovery of more extensive deterioration of the concrete piers than anticipated.
“Early in 2013, additional degradation was found on the columns of the piers,” Nagi said. “A new design for repair was devised: A new column was built within the old columns.
“Dismantling the existing structure was a much greater feat than what was originally anticipated by the contractor,” Nagi said. “In addition, the degradation of steel and concrete was greater than planned, and further design changes were required to keep the project moving forward.”
The project did indeed move forward. Beating the newly projected February 2014 date by more than four months, one lane of traffic in each direction on the Henley Street Bridge reopened in mid-October 2013. Crews continued to complete paving work, staining, striping, decorative and street lighting and a gas line that runs the length of the bridge.
TDOT Commissioner John Schroer was pleased with progress.
“Work has progressed rapidly over the past several months, and we are so pleased to be able to reopen this bridge to traffic before the busy holiday season. We realize the hardship this closure has placed on residents, business owners, and travelers. We appreciate the public’s patience as we move towards the total completion of this important rehabilitation.”
The revised completion date now calls for work to be completed in its entirety by June 3.
“This is a historic structure and a part of the Knoxville skyline,” Nagi said. “This will be a safer and more efficient bridge for motorists, bicyclists and pedestrians, and will add decades to the life of the bridge.”
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