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East Span Bids Slow Farewell to Truss

Tuesday, February 16, 2016

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The Oakland-San Francisco Bay Bridge has been the subject of much attention—winning awards, under scrutiny for leakage and corrosion, and for its artistic lighting system, and now eyes are turned to the careful, engineered demolition of the old East Span.

A 504-foot truss section of the old span was removed on Feb. 4 and slowly lowered using a strand jack to a two-barge setup below, Caltrans shared on its San Francisco-Oakland Bay Bridge Facebook page.

Unlike the quick and nearly invisible implosion of the old Bay Bridge Pier E3 in November, this phase of demolition encompassed two days’ worth of work.

The six-hour process of lowering the 2,500-ton steel truss section on day one was captured as a time-lapse video.

Over the course of two days beginning on Feb. 4, a 504-foot truss section of the Old Bay Bridge East Span was removed and slowly lowered using a strand jack to a barges below and relocated for disassembly and recycling.

After receiving the bridge segment, the barges carried it over the Pier 7 in the Port of Oakland for disassembly and eventual recycling, Caltrans Senior Resident Engineer Darryl Schram said in a Caltrans News Flash video.

Removing the ‘504s’

This was first of 19 trusses to be removed during the demolition of the original East Span of the Bay Bridge. The truss section, which stretches east of the cantilever to the Oakland shore, includes five 504-foot segments and 14 288-foot sections, according to Caltrans.

In 1935, the building of the “504s,” as they’re called, was relatively straightforward and used disruptive piles to hold the steel frame high above the bay. The lowering and dismantling process is more complex, but also more environmentally friendly, Caltrans said in a statement prior to the event.

The event took place over two days. Day one focused on severing the truss from its towers and beginning the slow decent toward the waiting barges. Day two was dedicated to setting the truss down on barges before moving it away from the site.

Photo of the Day: The first of the 4 million-pound 504' truss sections is cut and the specialized ‘strand jack’ technology is lowering this span down to a barge below. © 2016, Sam Burbank

Posted by San Francisco-Oakland Bay Bridge on Friday, February 12, 2016

 

This phase of demolition poses a particular challenge, Caltrans said: removing one member from a truss bridge can change the loads on the other section, which could create a “dangerous spring-action effect.”

To keep this from happening throughout the demolition process, Caltrans engineers are using a 3-D finite element computer program model based on structural analysis and historical records that shows the distribution of forces.

Additionally, a series of 90 retroreflector prism targets have been installed at key locations on the bridge. Throughout each stage of demolition, crews will be able to monitor span conditions. As sections are removed, target locations will be updated in the computer program, enabling comparison of data against the predicted locations in the finite element model software.

Photo of the Day. The view at 6 a.m. on Saturday, just before work resumed to lower the first of the 4 million-pound 504' truss sections and then "sail" it away. © 2016, Sam Burbank

Posted by San Francisco-Oakland Bay Bridge on Monday, February 8, 2016

 

As with the Pier 3 blast demolition, environmental measures are a priority for the truss removal. In this case, no piles are needed, which lessens environmental impact, and contractors are also working closely with a bird deterrence contractor and engineers to coordinate activities to avoid other impacts.

Ongoing Removal Work

This is the second part in a three-part process to dismantle the Old Bay Bridge, according to Caltrans. Phase one, the complete demolition of the cantilever section and S-curve to Yerba Buena Island, was completed the end of 2015.

Phase two continues with removal of the first five 504s and then removal of fourteen 288-foot truss span sections that extend to the Oakland shore.

Phase three will focus on the demolition of the remaining marine foundations.

   

Tagged categories: Asia Pacific; Bridges; Demolition; EMEA (Europe, Middle East and Africa); Environmental Protection; Latin America; North America; Program/Project Management; Steel

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