Engineers who design in earthquake-prone areas know that they need to design the seismic loads of their bridges to account for potential massive shifts during a quake. (This is what is legally known as the professional standard of care, which takes into account what similar engineers, in the same conditions and community, would consider acceptable design)**. The Dumbarton Bridge, the farthest south bridge across the San Francisco Bay, is no exception to this rule.
Currently, the Dumbarton Bridge is being renovated as part of the San Francisco Bay Area Toll Bridge Seismic Retrofit Program. When the bridge is finished (expected in early 2013), the bridge will increase its ability to move from 20 inches of lateral movement to as much as 42 inches of lateral movement.
The retrofit includes friction pendulum bearings designed by Earthquake Protection Systems, Inc., which will isolate the superstructure from two pier structures where the main span of the bridge meets the approach structures. A concrete taper will be used from the joints to the main span to ease the transition, as the approach span is 5 inches lower than the main span.
According to Earthquake Protection Systems president Victor Zayas, in a statement to Roads & Bridges magazine, the most critical part of the bearing is the bottom lining, which is a self-sacrificing, solid-lubricant polymer composite that was developed based on earlier research done by NASA in the 1960s.
Click here to read more on the Dumbarton Bridge retrofit.
** If you missed my post on the jury instruction on standard of care, be sure to check it out here.
Photo (c) Jill Clardy via CC.