|About Us | Gallery Search | About this Site | About Heavy Construction|
|Home > The Builders >|
A platoon of construction cranes, dramatically lined up like oversized sentries, hoist pieces of a super-sized erector set into place. This mechanical ballet is nearly awe-inspiring.
To some of the roughly 225,000 motorists passing within a few hundred yards, the cranes may be the first definitive sign that their 1936 steel stalwart is being replaced. Just to the north, the concrete understudy is rising slowly, taking shape from literally beneath the waters of San Francisco Bay.
At about 240 feet high and 164 feet across, the red cranes are hard to miss. They and the workers operating them are here to do most of the heavy lifting. Steel rebar cages, wood for forms, structural steel. Many of the parts going into the bridge and the tools to get them in place arrive on the arm of crane.
In the early stages of construction, just a half dozen cranes are seen on the job. But that number is going to rise to 14 as construction commences on all of the bridge`s piers in coming months.
The result will be a Bay Area skyline graced by these symbols of prosperity and progress - an elegant row of mechanical arms caught in an odd ballet of lifting and toiling.
The cranes themselves are loaded with superlatives. Each costs about $1.2 million. They were purchased by the joint venture of contractors, known as KFM, building the bridge project. With a 50,000-pound concrete counterweight, each can lift up to 24,696 pounds and move it anywhere in a 164-foot radius from the crane`s tower. Because of the way geometric forces interact with the counterweight, the crane can more than triple its capacity - up to 88,000 pounds if the weight is held no more than 54 feet from the tower.
The further the crane extends, the more bearing the load’s weight has on the crane’s slender structure. Therefore a crane’s capacity decreases in relation to the distance away from the tower the load is moved. This is geometry in action. To demonstrate this principle, hold a five or ten pound object close to your chest while keeping your feet together. As you move your arm and the object away from your body, notice how the object seems to become heavier, and it becomes more difficult to stay balanced.
Like the cranes themselves, the workers involved in their assembly and operation are highly specialized. And like the cranes, they go where the work is. Jerry Fender, Superintendent of Tower Cranes for KFMJV, has worked among the massive hoists for 20 years. When asked to list various job sites, the 54-year-old rattles off cities like a concert promoter.
But as construction gigs go, Fender said, the Bay Bridge is a bit different.
"This is a nice project here," he said sitting in a small office in a complex of temporary buildings. "You are involved in building things all your life, and it`s nice to build something that`s monumental," he said. "You can build a 50-story building in Chicago, but it`s just another 50-story building."
"A lot of the stuff we do is normal, mundane stuff that people don`t really think that much about. This is the kind of thing that you can look back on with your grandkids and say, `I worked on that,`" Fender said. He`s also no stranger to bridge projects. Fender worked on a state highway bridge over the Mississippi River between Quincy, Illinois and Taylor, Missouri. Like his current task, that project replaced a depression-era span.
Made in mainly in France and Germany by Potain, a European subsidiary of Wisconsin-based Manitowoc Company, the cranes arrive in Newark, Calif., by freighter, having passed through the Panama Canal during their journey to the west cost of the U.S. The actual tower portion is made in the US. The components, still in their 40-foot containers, are loaded onto 12 tractor-trailers and delivered to Oakland. There, the crew gets to work. "We preassemble the crane`s upper works on a barge, which is very unusual," Fender said.
Constructing the crane on a barge minimizes the amount of land used as a staging area for the project. The ironworkers and operators on the assembly crew then spend days building up the tower and doing final assembly work. Unlike earlier tower cranes held together with large nuts and bolts, the Bay Bridge cranes rely on a system of locking pins so that there is no danger that the fastening points will loosen over time. The pins also make assembly faster. Despite the new generation of fasteners, assembly is not exactly a snap.
"You are trying to marry this thing together and put a pin in it," Fender said, pointing up at a latticework of girders reaching for the clouds. "And meanwhile, the thing is moving six to eight inches up and down (because of small swells on the Bay)." Each `pin` weighs about 30 lbs and is about as wide around as a human wrist. The pins fit into a tapered hole on each piece and are held in place with lock pins of their own. When completed, the control cab stands 180-190 feet high. And it`s up to 240 feet to the top of the tower. Not bad for a week`s work.
Despite their commanding stature, the tower cranes aren`t the heaviest lifters around. Those jobs are handled by another piece of equipment more grandiose in scale. "A lot of the purpose of the tower crane is to lift lighter things that don`t need the capacity of a derrick barge," Fender said. Light and heavy in the construction world are on an entirely different scale.
is always of great importance.
"Anything you pick up with this crane is going to act like a sail," Fender said. When winds exceed 30 miles per hour, special warnings are issued. At 45 miles per hour, the crane`s brakes "push thru" and the crane adjusts like a weathervane, cuttingdown on potentially dangerous wind resistance.
The work on the bridge has only just begun and so have the careers of these monumental pieces of machinery. When the work on causeway section of the bridge is complete, projected for 2009, the cranes will be disassembled and sold.
Construction Close-Up / Archives