Posted on 14 October 2010.
By Tony Illia, Special to Boulder City Review
Hoover Dam is an awe-inspiring, engineering marvel whose construction has become the stuff of folklore. That sense of engineering bravado is back with a new bridge.
It, too, required a monumental construction effort. Like its neighbor, the bridge is also a monumental project built during a deep recession.
The official name is the Mike O’Callaghan-Pat Tillman Memorial Bridge, named after former Nevada Governor Mike O’Callaghan (1971-’79) and professional football star turned slain soldier Pat Tillman.
The dam was the largest structure of its kind 75 years ago. The 1,960-foot long bridge achieves a similar distinction as North America’s longest single-arch concrete span.
“It’s a well-known project in the engineering community,” Khaled Mahmoud, chairman of the New York City-based Bridge Engineering Association, said. “It’s the longest concrete single-arch bridge in North America, and the fourth longest in the world.”
The sleek, elegant structure stretches across Black Canyon in a single span, soaring 890 feet above the Colorado River.
The concrete-and-steel composite bridge has an iconic significance due to its commercial importance and proximity to the dam.
Yet, there is more to the $240 million project than meets the eye. Like Hoover Dam, which required nitty-gritty foundation work and diversion tunnels, the bridge similarly entails complicated but less visible site construction.
The components, though less spectacular, play crucial roles in the overall bridge program.
There are new four-lane roadways at each bridge end that tie into U.S. Highway 93, for example. The 1.8-mile-long Arizona approach, which finished in October 2004, has a small 900-foot-long bridge that spans a 200-foot-deep ravine on the east side of Sugarloaf Mountain.
It additionally has a new intersection at the Hoover Dam Access and Kingman Wash roads.
The 2.11-mile Nevada approach, meanwhile, finished in October 2005, roughly two months ahead of schedule. It consists of six new bridges over rocky terrain that includes a 463-foot-long, steel-girder structure over a 160-foot-deep gulch.
There is also a new four-lane highway alignment and a new traffic interchange at U.S. 93 near the Hacienda Casino.
The Arizona half was built by R.E. Monks Construction Inc. of Fountain Hills, Ariz., with Chino Valley, Ariz.-based Vastco Inc., while Edward Kraemer & Sons Inc., of Plain, Wis., did the Nevada side.
Eight large steel-lattice power towers carrying 230-kilovolt and 440-kilovolt electrical lines were also relocated away from the bridge path. The $9.6 million job was completed by Kansas City-based Par Electrical Contractors in 2003.
The bridge, meanwhile, was as big and complicated as it gets. A joint-venture led by San Francisco-based Obayashi Corp., with PSM Construction USA Inc., of Brisbane, Calif., won the contract in 2004 with a $114 million low bid. Its proposed cableway bridge-erection method helped it cinch the deal.
The contractor used four 330-foot-tall steel towers, two pairs on each side of the Black Canyon, with 2,500-foot-long, 3-inch-diameter cableways strung in between.
Bridge segments were moved into place using trollies attached to cables, or “high lines,” as workers called them. It’s essentially like a heavy-duty clothes line capable of carrying 50 tons worth of building materials.
A similar system was used during the construction of Hoover Dam. It’s the most practical way to move things over the canyon’s treacherous terrain and sheer drop offs. The high lines work something like an arcade game where players maneuver a mechanical claw over an item, lift it, and drop it into place.
“Cableways aren’t a common thing to use in bridge construction, but you’re dealing with a construction site that is 800 feet about water level,” said Mahmoud, who also serves as president of New York City-based Bridge Technology Consulting.
Not everything ran smoothly. In September 2006, the cableways collapsed under 55 mph winds, bringing construction to a standstill. The incident delayed bridge construction by two years.
Both the owner and contractor declined to comment further on the troubles. But, a replacement cableway system was designed and built from scratch by Cincinnati-based F&M Mafco. It was based on the original design but used “heavier components,” said Obayashi’s project manager Jim Stevens. The project soon found its stride again.
The 88-foot-wide bridge soars 870 feet above the Colorado River, a quarter mile downstream from the dam. The elegant structure is composed of reinforcing steel struts between twin concrete arch ribs. Struts add ductility to the lateral framing system for extreme seismic loads.
The bridge’s concrete deck and steel box girders are supported on 440 precast-concrete spandrel columns, each averaging 10 feet in length and stacked up to 280 feet high from the canyon floor.
The striking, 277-foott-deep twin-rib arch consists of 104 segments, each about 25 feet long. The bridge marks the culmination of several interlinking construction and design contracts, and years of planning and coordination.
Construction created 1,200 direct and indirect jobs. Yet, the economic impact of not building it is $100 million annually, the Federal Highway Administration said.
Talks for an alternate route over the dam dates back to the 1960s. U.S. Highway 93 currently runs over the crest of the dam, and often gets congested with traffic.
The route additionally has switchbacks and abrupt inclines that create safety concerns. The two-lane roadway, a key route in the North America Free Trade Agreement between the United States, Mexico and Canada, sees 17,000 vehicles daily.
It has also been identified as a high priority corridor in the National Highway System Designation Act of 1995, and it’s a part of the Canamex corridor linking Canada to Mexico. After the Sept. 11, 2001 attacks, security for the nation’s infrastructure and monuments was increased.
Truck traffic has since been diverted 23 miles away from the dam, costing consumers some $30 million annually. Other commercial four-lane routes add an additional 250 miles.
“Right now, our guys cannot go over the dam. They have to go through Laughlin instead,” Nevada Motor Transport Association Chief Executive Officer Paul Enos said. “The bridge is important for more efficiently moving commerce and goods throughout the West. It benefits everybody. There is nothing in society today that trucks don’t move, including clothes, food, and medicine.”
The bridge opens U.S. 93 as a major corridor in the movement of manufactured materials. Trucks currently deliver products and goods to 80 percent of all U.S. communities.
Rising fuel costs, growing gridlock and increased emissions standards could see more trucks abandoning Interstate 5 in California in favor of U.S. 93, which is characterized by long straight stretches with few steep grades.
“The new bridge will eliminate the sharp turns, narrow roadways, inadequate shoulders and low travel speeds of the existing travel route,” Federal Highway Administration project manager Dave Zanetell said. “This is really a historic project that has been a long time in the making.”
Tony Illia is a freelance writer focusing on the construction industry. He can be reached at email@example.com or 702-303-5699.
The Hoover Dam Bypass Bridge will be officially dedicated today with memebers of the O’Callaghan and Tillman families in attendance.
U.S. Transportation Secretary Ray LaHood will dedicate the Mike O’Callaghan-Pat Tillman Memorial Bridge at 10 a.m.
Federal Highway Administrator Victor Mendez and Arizona Gov. Jan Brewer will attend, as will Sen. Harry Reid and Rep. Dina Titus.
Nevada Lt. Gov. Brian Krolicki will attend on behalf of Gov. Jim Gibbons, who is still recovering from injuries sustained in a horse-riding accident.
It will be Saturday, however, when the bridge receives its first crush of curious onlookers onto its surface.
Nearly 20,000 people are expected to come to the bridge during a public party thrown by the Federal Highway Administration.
Bridging America is scheduled to run from 8 a.m. to 2 p.m. Reservations for the event were closed at 14,000. However, people involved with the event said no one will be turned away if their name is not on a list.
The event will feature a kids’ activity area, and other interactive displays explaining the history and building of the bridge.
The main attraction will be the 1,900-foot walkway on the Hoover Dam side of the bridge giving people a view of the historic dam previously only available from helicopters.