Bay Bridge Broken Rods; Is Iconic Structure In Danger Of Collapse?

By iScienceTimes Staff on March 27, 2013 4:39 PM EDT

Bay Bridge broken rods
The Bay Bridge in San Francisco. (Photo: Creative Commons)

The Bay Bridge broken rods, a series 9-16-foot steel rods that snapped under the eastern portion of the bridge, are being investigated by the California Department of Transportation (Caltrans) to determine if the bridge is safe for a re-opening set for Labor Day weekend.  The Contra Costra Times reports that the Bay Bridge's broken rods, which connect the bridge deck to a concrete cap on a massive pier, snapped when they were tightened.

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"Caltrans is diagnosing the problem and we are confident they will find a solution," said Metropolitan Transportation Commission spokesman Randy Rentschler late Tuesday. The commission is overseeing the new $6.4 billion span construction with the state.

Rentschler said that the Bay Bridge's broken rods are not being viewed as a significant structural problem and that the bridge should re-open on schedule. However, the Bay Bridge's broken rods are part of the seismic protection system in place on the span, meaning that a large enough quake could cause significant damage to the structure should it occur before necessary work is completed.

The Bay Bridge connects San Francisco and Oakland and sits near the highly active San Andreas fault line. Residents of the area know of the mythology of a massive quake referred to as "the big one," a magnitude 8+ quake that scientists expect could happen at any time and with little warning. The Bay Bridge's broken rods could be problematic if a once-in-a-lifetime quake struck the San Francisco region in the coming months.

To ensure the safety of the Bay Bridge, Caltrans will replace at least 32 bolts, and perhaps many others, attached to "shear keys," units that allow controlled lateral movement of the bridge in the event of a large quake. The bolts, also referred to as rods, attach four shear keys between the easternmost pier of the new suspension span and the roadway above it.

"We have surmounted far greater engineering challenges than this one in getting this bridge constructed," said Steve Heminger, executive director of the Metropolitan Transportation Commission, told the Sacramento Bee. "And I have no doubt that we will get through this one as well."

According to a Caltrans website about the history of the Bay Bridge, it was the largest and most expensive bridge of its time during its construction in the 1930s.

"Cynics believed that the bridge would be impossible to build due to the potential impact of turbulent waters and gusty winds. Engineers had assumed that the area's high winds posed a greater threat than earthquakes, despite the bridge's proximity to two major fault lines. The varying soils and water depths, the inaccessibility to bedrock, and the unique design challenges inherent in developing a bridge to span eight miles across the Bay led some to believe that building such a bridge was unthinkable," states the website.

The Bay Bridge's broken rods, however, are all too real for the engineers at Caltrans.

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