metro

Dumbarton Bridge Closes For Upgrades, Reopens Early

By Joseph Geha
Metro Editor

Photographer: Joseph Geha

Workers finishing pouring and smoothing a rubberized
concrete compound, which aids in impact absorption.

The Dumbarton Bridge closed over the entire Labor Day weekend, beginning Friday night at 10 p.m., so construction crews could make seismic upgrades to the eastern half of the incline.

Bay Area motorists were allowed back onto the bridge at 7:19 p.m. Monday, nine hours and forty-one minutes ahead of the scheduled reopening, Tuesday at 5 a.m.

The focal point of the entire operation was the installation of a new seismic joint, constructed of two steel plates laid over one another, 7 feet by 85 feet across, spanning all six lanes of traffic and the bike trail.

An identical joint was installed on the western span of the incline during the Memorial Day bridge closure.

The new hinge joint on the eastern
side of the Dumbarton, put in place
only hours before the bridge reopened.

The plates of the joint slide over each other, allowing for 42 inches of expansion and contraction within the deck of the bridge. In addition, the joint is bordered by rubberized concrete and a thick, solid slab of rubber, which will help absorb the impact of an earthquake.

According to Effie Miliones Verducci, Caltrans spokesperson for the Dumbarton, drivers on the bridge would still feel a quake, but the deck will not be in a state of major disrepair following that event.

A host of other operations were at play during the weekend while the joint was being laid down.

Crews in steel box girders underneath the incline area of the bridge worked to jack the traffic deck up five inches, to make space for new hydraulic bearings to be installed on top of the foundations that support the deck. This would further reduce the likelihood of the roadway absorbing the brunt of the force from a seismic event.

Those bearings will be installed during night closures and other scheduled work hours between now and early 2013, when the bridge upgrades are expected to be complete. There will be a total of 96 bearings, six per foundation on the 16 key foundations under the incline of the bridge.

“Really, just the work operations just all went smoothly,” said Miliones Verducci in a statement to the press, explaining Caltrans and the contractor, Shimmick, did their best to ensure that even if delays had occurred, there would not be a late opening. She also credited the favorable weather as an enabling element to the project’s expediency.

Crews cleaning up debris at the site of the new steel
seismic joint.

To work in conjunction with the road joint, the barriers that divide directions of traffic were replaced in small segments to make room for a new hinge joint, another complimentary stabilizing element.

Major safety upgrades aside, the toll plaza building was power-washed and new landscaping was installed, utilizing colored recycled tires to make pellets that mimic tanbark. New crash cushions were installed at the toll plaza, as part of a Caltrans effort to standardize them across the region.

To aid in traffic flow, the carpool lane has been changed to act as a FastTrack only lane, during non-carpool hours.

Once the Dumbarton retrofit is finished, the Bay Bridge will be the only remaining bridge in the region left without upgrades, which will be replaced by the nascent structure alongside the current span, to be completed in mid-2013.

This entry was published in The Pioneer Online on Thursday, September 6th, 2012 at 12:36 pm.