Natchez Trace Parkway Bridge
Encyclopedia
The Natchez Trace Parkway Bridge is a concrete
double arch bridge
located in Williamson County, Tennessee
, 14 km (8.7 mi) from the northern terminus of the Natchez Trace Parkway
. It is 479.1 m (1,571.9 ft) long and carries the two-lane Natchez Trace Parkway 44.2 m (145 ft) over State Route 96 and a heavily wooded valley
. The 177.4 m (582 ft) long main span is symmetrical, while the 140.8 m (461.9 ft) long second arch is not, due to the slope of the valley at the southern end of the bridge. The bridge is unique in that it does not use spandrel
columns to support the deck from the arch. Rather than being evenly distributed along the arch's length, the weight of the bridge is concentrated at the crown of the arch. The lack of spandrel columns results in a clean, unencumbered appearance.
The bridge, also known as the Natchez Trace Parkway Arches, is the first segmentally constructed
concrete arch bridge in the United States
. The arches comprise 122 hollow box segments precast in nearby Franklin
, each of which was about 3 m (9.8 ft) long and weighed between 26 and 41 MT (28.7 and 45.2 ST) . The deck consists of 196 precast post-tensioned trapezoidal box girder segments, each typically 2.6 m (8.5 ft) long. The sections atop the crown of the arch are 3.9 m (12.8 ft) deep. The foundations and piers of the bridge were cast in place.
The bridge was designed by Florida
-based Figg Engineering Group and built by PCL Civil Constructors Inc., a subsidiary of PCL Constructors Inc.
The arches and deck were constructed using a balanced cantilever
method. Each arch was supported by temporary cable stays anchored from the top of the piers and the valley sides until it was fully built. This procedure was chosen in place of conventional shoring
towers so that environmental damage to the valley would be minimized. The bridge cost US$11.3 million to build, and was completed in October 1993. It was officially opened on March 22, 1994.
The bridge has won many awards for its design, including a Presidential Award for Design Excellence in 1995, and an Award of Merit from the Federal Highway Administration
in 1996. The Eleventh International Bridge Conference named it the single most outstanding achievement in the bridge industry for 1994. The bridge "impressed the... jury with its aesthetically striking double-arch design, which shows exceptional sensitivity to the historical context of the site."
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
double arch bridge
Arch bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...
located in Williamson County, Tennessee
Williamson County, Tennessee
Williamson County is a county in the U.S. state of Tennessee. As of 2010 US Census, the population was 183,182. The County's seat is Franklin, and it is part of the Nashville-Davidson–Murfreesboro–Franklin Metropolitan Statistical Area. The county is named after Hugh Williamson, a...
, 14 km (8.7 mi) from the northern terminus of the Natchez Trace Parkway
Natchez Trace Parkway
The Natchez Trace Parkway is a National Park Service unit in the southeastern United States that commemorates the historic Old Natchez Trace and preserves sections of the original trail....
. It is 479.1 m (1,571.9 ft) long and carries the two-lane Natchez Trace Parkway 44.2 m (145 ft) over State Route 96 and a heavily wooded valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
. The 177.4 m (582 ft) long main span is symmetrical, while the 140.8 m (461.9 ft) long second arch is not, due to the slope of the valley at the southern end of the bridge. The bridge is unique in that it does not use spandrel
Spandrel
A spandrel, less often spandril or splaundrel, is the space between two arches or between an arch and a rectangular enclosure....
columns to support the deck from the arch. Rather than being evenly distributed along the arch's length, the weight of the bridge is concentrated at the crown of the arch. The lack of spandrel columns results in a clean, unencumbered appearance.
The bridge, also known as the Natchez Trace Parkway Arches, is the first segmentally constructed
Segmental bridge
As its name implies, a segmental bridge is a bridge built in short sections , i.e., one piece at a time, as opposed to traditional methods that build a bridge in very large sections...
concrete arch bridge in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The arches comprise 122 hollow box segments precast in nearby Franklin
Franklin, Tennessee
Franklin is a city within and the county seat of Williamson County, Tennessee, United States. The population was 62,487 as of the 2010 census Franklin is located approximately south of downtown Nashville.-History:...
, each of which was about 3 m (9.8 ft) long and weighed between 26 and 41 MT (28.7 and 45.2 ST) . The deck consists of 196 precast post-tensioned trapezoidal box girder segments, each typically 2.6 m (8.5 ft) long. The sections atop the crown of the arch are 3.9 m (12.8 ft) deep. The foundations and piers of the bridge were cast in place.
The bridge was designed by Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
-based Figg Engineering Group and built by PCL Civil Constructors Inc., a subsidiary of PCL Constructors Inc.
PCL Construction
The PCL family of companies is the largest general contracting organization in Canada and the sixth largest in the US. The organization is active in the commercial, institutional, multi-family residential, heavy industrial and civil construction sectors. The company's North American Headquarters...
The arches and deck were constructed using a balanced cantilever
Cantilever
A cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
method. Each arch was supported by temporary cable stays anchored from the top of the piers and the valley sides until it was fully built. This procedure was chosen in place of conventional shoring
Shoring
Shoring is a general term used in construction to describe the process of supporting a structure in order to prevent collapse so that construction can proceed. The phrase can also be used as a noun to refer to the materials used in the process....
towers so that environmental damage to the valley would be minimized. The bridge cost US$11.3 million to build, and was completed in October 1993. It was officially opened on March 22, 1994.
The bridge has won many awards for its design, including a Presidential Award for Design Excellence in 1995, and an Award of Merit from the Federal Highway Administration
Federal Highway Administration
The Federal Highway Administration is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two "programs," the Federal-aid Highway Program and the Federal Lands Highway Program...
in 1996. The Eleventh International Bridge Conference named it the single most outstanding achievement in the bridge industry for 1994. The bridge "impressed the... jury with its aesthetically striking double-arch design, which shows exceptional sensitivity to the historical context of the site."