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Public Roads - March/April 2011

March/April 2011
Issue No:
Vol. 74 No. 5
Publication Number:
Table of Contents

A Majestic Showcase

by Doug Hecox

The new Hoover Dam bridge reaffirms that American engineering can build great infrastructure despite the current economic challenges.


Shown here is the new Mike O’Callaghan-Pat Tillman Memorialn Bridge, which is located at Hoover Dam east of Las Vegas on the Arizona-Nevada border. At the October 14, 2010, dedication ceremony, Transportation Secretary Ray LaHood said that the bridge is "proof positive that America is not afraid to dream big."


Soaring protectively near the Hoover Dam and straddling the boundary between Arizona and Nevada, the Mike O’Callaghan-Pat Tillman Memorial Bridge has made history several times over. Not bad, considering that the bridge -- one of the world’s largest -- was once thought to be unbuildable.

Once the new bridge began carrying thousands of vehicles and trucks every day over Black Canyon, the structure became one of the most awesome anywhere. Towering nearly 900 feet (274 meters) above the Colorado River, the bridge sits atop the world’s tallest precast concrete columns. Its central span -- at 1,060 feet (323 meters) long -- is the Western Hemisphere’s longest single-span concrete arch.

At the project’s dedication on October 14, 2010, U.S. Transportation Secretary Ray LaHood said, “This majestic bridge reaffirms a powerful idea. Americans can still build great things -- not just in spite of enormous economic challenge, but as the means of overcoming it.” The bridge was opened to traffic on October 19, 2010.


The dedication drew a crowd of nearly 2,000, including members of the O’Callaghan and Tillman families. O’Callaghan was a former governor of Nevada, and Tillman was a professional football player with the Arizona Cardinals who lost his life serving in the U.S. Army in Afghanistan in 2004.

Federal Highway Administrator Victor Mendez, the event’s master of ceremonies, enjoys a unique perspective on the project. As director of the Arizona Department of Transportation from 2001 until 2009, Mendez played a critical role in ensuring the project had the funds it needed from Arizona and Nevada. Together, the two States provided $140 million, primarily through bond funds -- representing more than half the project’s total cost. Their partnership was widely considered vital to the project’s completion. Through a variety of Federal funding measures, the Federal Highway Administration (FHWA) provided an additional $100 million.

“This bridge is a unique accomplishment for the Nation,” Mendez said at the ceremony. “This is the kind of smarts and attitude we need to bring in more of these projects and put more people back to work. The bridge shows what we can achieve when we set aside individual agendas and work toward a partnership. I hope [it] serves as a model for the future.”


In 1928, the Federal Government began planning construction of a hydroelectric dam on the lower Colorado River. Three years later, construction of the mammoth project began, led by engineer Frank Crowe. Thousands of people worked round-the-clock, 7 days a week, in triple-digit heat to complete the dam by September 30, 1935. By every standard, it remains one of history’s greatest engineering feats and an icon of America’s can-do attitude.


The new structure is the Western Hemisphere’s longest single-span concrete arch bridge and one of the tallest in the world. Seen here is a view during the finishing of the bridge deck in April 2010.


Innovations borne of the project’s difficult conditions forced early engineers and construction workers to develop solutions that have become staples of the modern construction industry, including hardhats and onsite fabrication of steel pipe.

A narrow two-lane highway running across the dam’s crest connected Arizona and Nevada on either side of Black Canyon. The volume of traffic served by the two-lane U.S. 93 was initially small but swelled significantly in the decades that followed.


Posing at the dedication ceremony are (left to right): U.S. Representative Dina Titus (D-Nev.), U.S. Transportation Secretary Ray LaHood, Federal Highway Administrator Victor Mendez, Arizona Gov. Jan Brewer (R-Arizona), U.S. Senator Harry Reid (D-Nev.), and Nevada Lt. Gov. Brian Krolicki (R-Nev.).


By the 1980s, the Hoover Dam road was a major traffic chokepoint between Las Vegas and Phoenix, each of which had grown substantially during the intervening years.

In the late 1980s, the U.S. Department of the Interior’s Bureau of Reclamation (BOR) created the Colorado River bridge project management team to plan a new bridge. An environmental study began in 1990 but, 3 years later, BOR withdrew as the project’s lead agency. Work stopped until 1997, when FHWA’s Central Federal Lands Highway Division agreed to lead the project.

After extensive research, FHWA selected the Sugarloaf Mountain alternative, which included a 1,900-foot (579-meter) river crossing about 1,500 feet (457 meters) downstream from the dam. This site would require 3 miles (4.8 kilometers) of new highway approach in Nevada and about 2 miles (3.2 kilometers) of new highway approach in Arizona. The bypass also features eight other bridges and numerous animal underpasses to help the area’s mountain sheep cross U.S. 93 without putting themselves or drivers at risk.

In 2000, FHWA offered Central Federal Lands engineer Dave Zanetell -- widely known as “Z” -- the position of project manager. Fully aware that the Hoover Dam bypass project would be a mammoth undertaking, he was cautious.


Here the dam is shown in the foreground, the new bridge behind it, with both structures rivaling the magnificence of the surrounding mountains.


Many of his peers tried to discourage him from taking on the project. His colleagues told him, “That job will never be properly funded. Two hundred forty million is not nearly enough for a bypass like this. Stakeholders will never support the job. It’s a pipe dream. It’s career suicide.” And so on. But Zanetell thought about it and “realized that nothing great -- certainly, no great public works project -- ever happened because it was easy.”

As he did playing football for the Colorado School of Mines, Zanetell tackled the challenge head on. “I never had a doubt about this project -- not one,” he says. “I have to believe that Frank Crowe, who had my position with the construction of the Hoover Dam, was surrounded by people who were naysayers. I know for a fact he never doubted. I think it’s important that, when you’re leading the effort, your team knows, ‘Our leader has no doubt.’”


This aerial photograph shows the bridge with the approach segments of the new bypass, straddling the State line between Arizona (in foreground) and Nevada.



Unlike other bridges, which are typically constructed from the ground up, the O’Callaghan-Tillman Bridge was built from the top down. Extensive cabling above the canyon transported materials from one side to the other while workers lowered key components of the bridge into place.

“Right out of the chute, we had to gain access to the canyon to construct the foundations,” says Zanetell. “Physically, there were significant challenges: getting off the canyon wall, containing rockfalls, and so on. Also, we had to design the plan so there were simultaneous activities. We were building precast segments near Las Vegas while we were fabricating steel girders in Oregon for the superstructure.”


This view of the future bridge alignment was taken from Abutment 2 (Arizona) looking west toward Abutment 1 (Nevada) in January 2006. Visible in the foreground is a tower crane erected on the left footing of Pier 15. In the background are the footings and excavations for Abutment 1, Piers 1 through 5 (Nevada skewback), along with a tower crane erected on the left footing of Pier 4.


Relocation of electrical utilities from south of Hoover Dam began in 2002, and preliminary engineering for the bypass itself began in early 2003. Construction of the O’Callaghan-Tillman Bridge -- the largest span of the nine bridges used in the bypass -- began in early 2005.

“The initial access, the first little notch in the canyon wall -- what we call ‘getting a toehold’ -- was mostly done by hand,” says Zanetell. “Literally with a single worker on a little crane and a jackhammer. Eventually we could get a larger drill down there, and the toehold got big enough to lower in a full-size excavator.”

Rockfall was a challenge for the Hoover Dam construction 75 years earlier and remained a problem for workers building this bridge. “It’s just a different day and age,” Zanetell adds. “When the dam was built, there weren’t major rockfall containers like we have today. Everything we did was small scale and contained, so rock would not be allowed to release into the canyon. It was measured, careful, and surgical.”


Shown here in June 2006 are the approach spans looking from Pier 3 to Abutment 1.


While the excavation took place, 440 column segments were precast offsite. Because every segment had to fit together perfectly, the challenge was to ensure that they were sized correctly and not too large for the crane to lift into place. The process required extraordinary attention to detail, engineering analysis, and execution.

Constructing the arch was a sequence of specific steps. The arch is flexible and allows the weight of vehicles and the bridge itself to be borne by the canyon walls. It was not constructed with precast segments hoisted into place but rather by pouring concrete in place into each of 26 sections, one after the other, until both legs of the arch met in the middle for a closure casting.

After we completed one of the segments on the arch, we would then advance the form traveler,” says Zanetell. “The traveling frame would fit like a sleeve over the completed section and then we’d bring in the rebar to set in that form. Then we’d pour the concrete, connect the next set of cables or stays, and slide it forward and do it again. It’s kind of a repetitive process, but as we went along, it kept sequentially building the tension in the structure. It was meticulous and methodical, and not a brute force effort.”


These constructed stay cables, stored on the Nevada approach bridge deck, are part of the cable-stay erection system that supported the arch ribs until closure.


Workers are shown placing concrete for the bridge’s deck section in June 2005.


This view of the bridge, taken in August 2009, shows the Nevada approach (left) with the arch headings projecting outward to segment 26 with all stay systems installed. The Arizona approach (right) is visible with the arch headings also projecting outward to segment 26 with all stay systems installed.


Zanetell continues the story: “Bringing the arch together was a moment of incredible pride for the trade and craft workers who had worked toward it. By the time we got to the deck, which is a relatively routine engineering act, we were looking to build a great one. We focused on all the little details that can be the difference between an average job and a great job. It’s like the entryway to your house: it’s the most visible part. We wanted to make sure the faceplate of the job was done right.”

With summer temperatures routinely topping 120 degrees Fahrenheit (49 degrees Celsius) and high winds year-round, workers on the project endured hostile weather and scorching temperatures.

“Ensuring workers were adequately hydrated was critical, but the local trade and craft workers were pretty hardy,” says Zanetell. “It has to be said that this bridge wouldn’t have been possible without the collective skills of the project’s many workers, design engineers, erection engineering consultants, and construction contractors who shared our vision of building a world-class bypass. Everybody accepted the heat as a part of the challenge, but having the dam nearby helped to motivate us all.”

Zanetell is modest about the achievement of his team: “We believe we have done something very special and very great, but we know that Hoover Dam will always be number one. It was an incredible engineering feat.”


The ambitious project employed more than 1,200 workers. Here, the new engineering marvel soars over the dam.


Nevertheless, the new span is a magnificent accomplishment. “When people physically see the bridge firsthand, they can’t believe the magnitude of it,” he adds. “What is clear is that a project of this magnitude can be done on budget, with fiscal responsibility from day one. I feel like we have an obligation to take what we’ve done here and apply it elsewhere.”

Secretary LaHood agrees. “I am overwhelmed by the human achievement the bridge embodies -- engineers, crane operators, and concrete workers. Like the Hoover Dam upriver…this marvel is a monument to America’s can-do spirit... In solving the problems of the clogged Hoover Dam crossing, we have demonstrated once again our ability to tackle a complex challenge with American ingenuity and dedication. We can still dream big. We can roll up our sleeves and make this Nation’s infrastructure the envy of the world once again.”

Some Key Facts

The Mike O’Callaghan-Pat Tillman Memorial Bridge is the fourth-longest single-span concrete arch bridge in the world. In addition:

  • Each arch rib is made up of 56 cast-in-place sections with construction starting from the canyon walls and a closure pour that locks the two halves together.
  • Approximately 9,000 cubic yards (6,881 cubic meters) of 10 kips per square inch (68.950 megapascals) compressive strength concrete is cast in the arches.
  • The outer dimensions of each hollow arch rib are 20 feet (6 meters) wide by 14 feet (4 meters) tall, with 14 inch (36-centimeter)- thick walls.
  • Structural steel struts connect the arches at each column and are covered with precast concrete panels. The largest struts weigh nearly 45 tons (41 metric tons).
  • The 440 10-foot (3-meter)-tall concrete segments were each precast offsite and erected to form the pier columns. At 290 feet (88 meters), the tallest of the precast columns are the world’s tallest of this type.
  • The structural steel tub girders were fabricated offsite and placed with the cableway cranes. The heaviest girder was nearly 50 tons (45 metric tons).
  • The temporary cable stay tower and support system for erection of the arch incorporated more than 2 million feet (609,600 meters) of cable-stay strand.

Doug Hecox is a spokesman with FHWA’s Office of Public Affairs. He has a journalism degree from the University of Wyoming, teaches journalism and public relations writing at American University, and has authored two books.

For more information, contact Doug Hecox at 202–366–0660 or

Correction: This article was changed in this online version and differs from the printed version in the following manner: Arizona Gov. Jan Brewer (R-Nev.) was changed to: Arizona Gov. Jan Brewer (R-Arizona).