The Benecia-Martinez Bridge and the Giant Ball Bearing
When considering standard ball bearing sizes we may consider tiny ball bearings, such as those used in miniature computer hard-drives or in medical machinery, but we rarely think about the over-sized ball bearing. The Benecia-Martinez Bridge in California is a network of three bridges, and is thought to use the biggest ball bearing mechanism in the world. This article will give an overview of other uses of large ball bearings before going on to explore the construction of the bridge and what engineering capabilities such massive ball bearings provide.Miller Park
Although the Benecia-Martinez bridge is thought to use the biggest ball bearings in the world, the athletic stadium, Miller Park in Wisconsin is certainly a contender. The stadium is one of the largest construction projects ever undertaken in the history of Wisconsin. It took five years to construct and was completed in 2001 costing $290 million of public funds. Miller Park is the only sporting venue in North America to use a fan-shaped convertible roof which can be opened and closed in ten minutes. The roof has large glass panels to allow natural light through, so grass can grow and the stadium can be heated up to 30C making spectators more comfortable than in an open air stadium. Ball bearings are used to open and close the gargantuan roof structure, which is over 17 feet high. Large ball bearings are used to open and close the stadium roof which is up to seventeen feet high.The Benecia-Martinez Bridge
The Benecia-Martinez Bridge is the collective name for three parallel bridges which span the waters of the Carquinez Strait. They link the Northern Benecia to the Southern Martinez. Originally the bridge consisted of a concrete structure built in 1962 as a replacement for a car ferry service across the water. The newest part of the bridge was constructed in 2007, and today up to 100,000 vehicles are carried across the strait daily.
Seismic features were gradually retrofitted to the bridges to ensure the durability and safety of these huge structures which cost $122 million. Both the superstructure and substructure of all the bridges were strengthened to withstand forces from natural disasters like earthquakes. All expansion joints were replaced with larger steel joints, expansion hinges, steel members and the lateral bracing systems were either strengthened or replaced. A seismic monitoring system was also installed and, most importantly, seismic isolation bearings were fitted.
These bearings were the largest pendulum friction bearings ever made. Each bearing is at least 12 feet in diameter and weights between 40,000 to 50,000 pounds. When an earthquakes hits, these bearings will allow for up to six feet of horizontal movement to occur with minimal structural displacement, making them pretty unrivalled internationally.
So next time you consider the ball bearing as the kind of object you can fit in your hand, remember the Benecia Bridge and its 40,000 pound bearings. The construction of the bearing alone is a marvel in engineering and, set in place, demonstrates just how advanced contemporary structural engineering can be.
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