Tags

, , , , ,

The  Navajo Bridge was originally built by the Arizona Highway Department, and designed by the Kansas City Structural Steel Company in 1929.105NavajoBridgeSignHowever, When the original bridge was built in 1929, building regulations were different. The original bridge’s maximum load capacity (22.5 tons) was not designed to support heavier modern day vehicles. Both the loads and widths of these modern day transportation vehicles are a lot larger than the trucks used in 1929.0Due to the mentioned transportation problems, state officials made the decision that something needed to be done about the old bridge. They had to summit a cost proposal and a design proposal for the bridge. The Arizona State Department of Transportation looked at all the proposals of the different engineering firms and decided to hire Cannon and Associates.

Navajo_Bridge_003

Cannon and Associates needed to follow the National Environmental Policy Act, which requires organizations to examine the environmental consequences of any project about to be undertaken. In the Navajo Bridge Project, consideration was given to the endangered species, the rock falling into the canyon, disturbance of the water, not damaging the sides of the canyon, plus deciding what was going to be done with the existing bridge which was on the historic register. When an item is listed on the historic register the item is only allowed to be fixed or improved, but it cannot be destroyed (Cannon 2000). 2

Measures that were taken to build the bridge in accordance to the National Environmental Policy Act were:

1. The new bridge would be built in the same style as the original bridge, which was a steel spandrel structure.

2. The original bridge would remain undisturbed and be used as a pedestrian bridge.

3. Material would be kept from falling into the Canyon.

4. A visitor center would be built to inform visitors about the history of the site, the vistors center which can be seen in the below picture was designed to blend into the environment by using similar rocks on the outside of the structure that would be found in the surrounding environment.

5. Special measures were to be taken to not destroy a endangered species of cactus that was found on the canyon walls (Cannon 1994).7

The new Navajo Bridge in Grand Canyon National Park is the only crossing of the Colorado River for a stretch of 965 km (600 miles). The $15 million steel arch bridge carries traffic across Marble Canyon, 143m (470 feet) above the Colorado River. The 1929 Navajo Bridge remains a pedestrian bridge. High strength steel was used in the new bridge in order to be visually compatible with the historic bridge and its setting. Source: fhwa.dot.gov

 8

Bridge Facts and Figures: Source: nps.gov

Navajo Bridge Historic Bridge Modern Bridge

Total Length

834 feet (254 m) 909 feet (277 m)
Steel Arch Length 616 feet (188 m) 726 feet (221 m)

Arch Rise

90 feet (27.4 m) 90 feet (27.4 m)
Height Above River 467 feet (142 m) 470 feet (143 m)
Width of Roadway 18 feet (5.5 m) 44 feet (13.4 m)
Amount of Steel 2.4 million pounds (1.1 million kg) 3.9 million pounds (1.8 million kg)
Amount of Concrete 500 cubic yards (385 cubic m) 1790 cubic yards (1370 cubic m)
Steel Reinforcement 82,000 pounds (37,000 kg) 434,000 pounds (197,000 kg)

Construction Cost

$390,000 $14,700,000
 The bridge has been designated as only the fourth NATIONAL HISTORIC MONUMENT by the American Society of Civil Engineers (ASCE) Source: ASCE

4

References

Excellence in Highway Design – Navajo Bridge Over Grand Canyon. (n.d.). Retrieved from https://www.fhwa.dot.gov/eihd/navajo.htm

Historic Navajo Bridge | ASCE Arizona Section. (n.d.). Retrieved from http://www.azsce.org/historic-navajo-bridge/

Navajo Bridge – Glen Canyon National Recreation Area (U.S. National Park Service). (n.d.). Retrieved from http://www.nps.gov/glca/historyculture/navajobridge.htm

Rowland, S. (n.d.). Navajo Bridge Project. Retrieved from http://enpub.fulton.asu.edu/structures/SlideCollection/ThumbNails/Navajo%20Bridge%20Project.htm

Advertisements