The Dangerous Art of Tearing Down Bridges, Dams, and Aircraft Carriers
History venerates the builders of great bridges, dams, and towers. But rare are commemorative plaques for the un-builders—those charged with the equally heroic task of dismantling those grand structures, once they become dowdy, obsolete, or downright dangerous. Herewith, five case studies in the art of mega-destruction—starting with the old, seismically shaky eastern span of the San Francisco–Oakland Bay Bridge. Also: remodeling NASA’s rocket assembly building, scrapping the world’s longest aircraft carrier, recycling a supercomputer, and moving a river to remove a dam.
1. Last Exit for the Bay Bridge
The original eastern span of the San Francisco–Oakland Bay Bridge, photographed from the Oakland side on November 8, 2013. The new bridge can be seen at right.
Demolition began: November 2013 | Duration of project: 3 years
Built during the Great Depression, the eastern span of the San Francisco-Oakland Bay Bridge was a marvel of utilitarian efficiency. (Some of the construction cranes were even incorporated as part of the structure.) But now that its graceful replacement is operational, the old span has to be taken down—without dropping anything into the water. Expected cost: $240 million. —Eric Smillie
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| To figure out the best sequence for removing the high-tension pieces, engineers will use a 3-D model, based on structural analysis and historical records, that shows how the forces are distributed. Bryan Christie Design |
Control the Tension
The piers of the cantilever truss aren’t holding the bridge up. They’re holding it down. “This is like a highly strung bow,” says senior bridge engineer Brian Maroney. (A bow made of 50 million pounds of steel.) “You don’t want to just cut the bow because the thing will fly off in all directions.” So crews will first remove the pavement on the upper deck to lighten the bridge’s load and reduce the tension. Next they’ll isolate steel supports, jacking them out of tension until they can be cut without whipping apart. Then they’ll slowly release the jacks.
Cut the Truss Spans
Named for their length in feet, the 504 and 288 truss spans are not under as much tension as the cantilever, so there’s less chance they’ll explode in your face when you cut into them. Still, caution is called for: The 80-year-old steel is not like modern steel; crews must be prepared for differences in strength and hardness.
Cart the Pieces Away
The steel beams are coated with greenish-gray paint, under which is a coat of lead-based stuff. To avoid contaminating the bay, all that metal has to be trucked away and cleaned, after which it will be resold as scrap.
Build a Monument
The massive art-deco column of pier E1, near Yerba Buena Island, may be preserved as a monument to the bridge that served the Bay Area for 77 years. The E2 pier will also likely remain and be converted into an observation platform for the new span.
Blast Foundations
The foundations of piers E3 to E5 are like honeycomb inside. One idea for demolition: Drill into them, plant a series of computer-controlled explosives around the internal walls, set off the charges, and let the concrete collapse into the void.
Mind the Birds
The shallow-water foundations of piers E19 to E22 may be saved for a new pedestrian walkway and bird sanctuary. On the bridge itself, a long-armed snooper truck will be used to install spikes to deter nesting. Any avian holdouts will be removed by hand.
L-Dopa.
2. Remodeling a Rocket Hangar
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The space shuttle Atlantis suspended in the towering Vehicle Assembly Building in 2010. |
The NASA Vehicle Assembly Building at Kennedy Space Center is big. Big enough to house the Saturn V rocket that propelled men to the moon. Big enough to have its own weather system (mist can form along the ceiling on humid days). And now it’s getting an overhaul: The seven fixed platforms of the VAB’s High Bay 3 must be detached, moved outside, and demolished to make way for a modular system that can better accommodate a variety of different rockets and exploration programs. Here’s how contractors are completing one of the world’s largest renovation projects. —Bryan Gardiner
Old Platforms Out
The first step was to remove the seven huge steel platforms (weighing 140 to 230 tons apiece) that once hugged shuttles and rockets. Precise centers of gravity had to be calculated for each of these multistory structures. After wiring and utility systems were disconnected—including some 700,000 feet of copper cabling—the platforms were detached and slowly lowered to the floor by a ceiling-mounted bridge crane. Careful movement was essential to prevent sway. Good thing this crane is precise enough to touch its load to an egg without cracking it.
New Platforms In
The old fixed platforms will be replaced with a modular system of 10 platforms that can be repositioned vertically and horizontally. That flexibility will be crucial for NASA’s new Space Launch System, which will rival the Saturn V rocket in size and is designed to offer a variety of configurations for different missions. The facility is also expected to host much smaller rockets from commercial space companies.
3. The End of the Enterprise
Launched in 1960, the USS Enterprise was the world’s first nuclear-powered aircraft carrier. The ship is 1,123 feet long from bow to stern.
Demolition began: 2012 | Duration of project: 14 years
After more than 50 years of service—including a cameo in Top Gun—the 100,000-ton USS Enterprise was inactivated in late 2012. It will be the first nuclear aircraft carrier of this class to get dismantled (in fact, “Big E” is the only ship of its class ever built), and the Navy estimates the project will take about 14 years. —Bryan Gardiner
1. Ordnance Off-Load
To transfer some of the ship’s munitions, Enterprise crew members fired shot lines over to the USNS Sacagawea and used them to string messenger lines made of wire rope. Then, while the ships traveled for hours through the Atlantic, just 30 yards apart, they slid ammunition packages across the water. Sounds crazy, but this sort of at-sea transfer has been used for supply replenishment since at least the late 1800s. The remaining ordnance was airlifted across in 946 helicopter trips.
2. Interior Stripping
On December 1, 2012, the carrier pulled into Norfolk, Virginia, and its contents were stripped—tools, furniture, linens, technical manuals, spare parts, cryptographic equipment. Cranes removed weapon launchers, anchors, antennas, and other large items.
3. Defueling
In June 2013, tugboats towed the ship across Hampton Roads harbor to Newport News Shipbuilding, where her keel had been laid in 1958. (Many of the workers taking her apart are the offspring of those who built her.) Crews then remove the fuel from the eight reactors, but exactly how they do it is classified. The empty compartments, along with their radioactive piping systems, are eventually sealed shut.
4. Spent Fuel Removal
The spent nuclear fuel is placed in containers with 14-inch-thick stainless steel walls (each cask weighs about 350,000 pounds). The containers are then loaded onto trains and trundled off to the Naval Reactors Facility at the Idaho National Laboratory for analysis and storage.
5. Towing
Onward! To the Puget Sound Naval Shipyard in Bremerton, Washington, via the scenic route. The Enterprise won’t fit through the Panama Canal, so a tugboat will pull the hulk around Cape Horn and up the Pacific Coast. During the four-month trip, the two vessels will be anywhere from 1,200 to 2,000 feet apart, depending on the waves: Ideally, when the tug goes up on a wave, the carrier should too. Constant adjustments to the tow length keep them in sync.
6. Scrapping and disposal
Each steel-encased reactor will be moved by barge from Puget Sound to the Hanford nuclear storage site, where it will be buried in a radioactive package that also includes other nasties like asbestos, cadmium, arsenic trioxide, cyanacrylate adhesive, and paints containing cyanide, coal tar epoxy, and chromium trioxide. And the 60,000 tons of steel in the hull? Chopped up and recycled, of course.
4. Recycling a Supercomputer
The IBM Roadrunner was once the fastest computer in the world. Today it’s obsolete. But you can’t just toss a supercomputer in your neighborhood e-waste bin. Bryan Christie Design
Demolition began: 2013 | Duration of project: 1 month
Supercomputers are typically retired after about five years, and one of the latest to get its pink slip is Roadrunner, which was officially shut down on March 31, 2013. Built by IBM and installed in 2008 at the Los Alamos National Laboratory, this $121 million daisy chain of 296 server racks and 122,400 processor cores helped model everything from the decay of the US nuclear weapons arsenal to how white dwarf stars explode into supernovas. Scrapping the housings and connections was the easy part; steel, copper, and plastic components were all shredded. But Roadrunner also contained 34 disk drives, some of which almost certainly held sensitive information. Los Alamos doesn’t share the specifics of the removal and destruction process, but previously published guidelines from the US Department of Energy and the National Institute of Standards and Technology provide a sense of how it works. —Bryan Gardiner
Overwrite, then apply magnets … or destroy completely.
First, technicians overwrite data three times, twice with pseudo-random patterns and once with a known pattern. Then some disks are demagnetized, while others may be sent to a separate metal-destruction facility. Some places use a disk sander to abrade the recording surface. Others feed disks into a crusher, which pushes a steel piston through the center of the drive. Still others apply concentrated hydriodic acid solution.
5. Moving a River to Remove a Dam
To raze the San Clemente Dam, engineers first have to divert the water.
Demolition began: 2013 | Duration of project: 3 years
California’s San Clemente Dam opened in 1921, and today its reservoir is choked with silt. That means an earthquake or flood could send a wall of mud sliming down the Carmel River and the valley below, damaging more than a thousand buildings. So dam owner California American Water and state and federal resource agencies decided to take it down. Dynamite isn’t an option because of the dirt and water that would spew forth, so engineers decided to move the river instead. —Eric Smillie
Cut a Notch
Crews are going to cut a 450-foot-long canyon through the ridge behind the dam and carve a new river channel around the sediment to neighboring San Clemente Creek. “I’m not aware of any other dam removal project that’s looked at that type of option,” says Richard Svindland, director of engineering for California American Water. “River rerouting is tough to do.” This Herculean task, the largest dam removal in state history, will involve building a diversion dike to direct the water along its new course.
Demolish the Dam
To make way for the water, workers will haul 380,000 cubic yards of sediment from San Clemente Creek (where the new river will run) and dump it on the main heap of silt, which will remain permanently. Then they’ll pick the dam apart with hoe rams. Eventually, the rerouted river will flow through the spot where the structure once stood.
Watch and Wait
In five years, California American Water will hand the site over to the Bureau of Land Management. “Ideally, 20 years from now,” Svindland says, “you won’t know that a dam was ever there.”
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