Eastern span replacement of the San Francisco – Oakland Bay Bridge

Proposed replacement span

Obsolete eastern span and replacement construction

Work is ongoing on the eastern span replacement of the San Francisco–Oakland Bay Bridge. The new eastern span is currently scheduled to open to traffic in 2013.^[1] The original San Francisco–Oakland Bay Bridge, built in 1936, became the subject of concern after a section collapsed during the Loma Prieta earthquake on October 17, 1989.

Earthquake damage

Collapsed section of the Bay Bridge after the Loma Prieta earthquake in 1989.

During the 1989 Loma Prieta earthquake, which measured 6.9 on the moment magnitude scale, a 50-foot (15 m) section of the upper deck of the eastern truss portion of the bridge collapsed onto the deck below, indirectly causing one death at the point of collapse. The bridge was closed for a month and one day as construction crews repaired the fallen section. It reopened on November 18, 1989.

Given the distance to the epicenter of the Loma Prieta (roughly 70 miles or 113 kilometers south of San Francisco), there was great surprise at the localized destruction around the Bay Area. Analysis points to the likelihood of reflected seismic waves from deep earth crust discontinuities. Failures were mostly located in areas of poor soil conditions due to building over filled-in creeks or on sand and rubble mixes from the 1906 earthquake—all of which were saturated with water and prone to liquefaction. (An exception was the Cypress Viaduct collapse, blamed on poor engineering in certain details, combined with large-structure resonances that had not been considered during design.)

It was clear that the eastern span must be made earthquake resistant. It had been known for over thirty years that a major local earthquake on either of the two local faults (the San Andreas and the lesser-known but far more dangerous Hayward) would destroy the major cantilever span. Estimates made in 1999 placed the probability of a major earthquake in the area within the following 30 years at 70 percent, although recent studies announced in September 2004 by the United States Geological Survey have cast doubt on the (statistical) predictability of large earthquakes based upon the duration of preceding quiet periods, while an even more recent (2008) analysis has increased the probability of a major event on the Hayward Fault^[2].

Initial retrofit proposal

The initial proposal for the eastern span involved the construction of substantial concrete pylons to replace or supplement the existing supports. There would also be modifications to the lattice beams as is now complete for the western span. The original cost estimate for this refit was $200 million. The overall appearance would be little changed. Owing to the retention of the original structure the bridge's ongoing maintenance costs would continue to be high compared to a replacement span.

Initial replacement proposal

Engineering and economic analysis in 1999 suggested that a simple replacement bridge would cost a few hundred million dollars more than a retrofit of the existing eastern span and that a replacement would have a far longer expected useful life — perhaps 75 to 100 years rather than 30 — and would require far less maintenance. Rather than retrofit the existing bridge the authorities decided to replace the entire eastern span. The design proposed was a simple elevated viaduct consisting of reinforced concrete vertical pylons and post-stressed precast concrete segment spans as seen in the lower right panel of the six alternatives illustration. The design criterion was that the new bridge should resist an 8.5 magnitude earthquake on any of several faults in the region, but particularly the nearby San Andreas Fault and the Hayward Fault. The aesthetics of the proposal were not received well by either the public or their politicians, being characterized as a "freeway on stilts".

Signature span proposals and selection

Original and final eastern span proposal

A design contest was held for a "signature span" (a span with distinctive and dramatic appearance, unique to the site) by the Engineering and Design Advisory Panel (EDAP) of the Metropolitan Transportation Commission (MTC). A number of innovative proposals were examined until all but four proposals that were submitted by members of EDAP were selected as semi-finalists, and a winner was selected from this group.

This posed a serious conflict of interest, as members of the Engineering and Design Advisory Panel (EDAP) who were selecting the bridge design reviewed proposals by their own firm and rejected all proposals that did not have a representative on the EDAP.

Construction begins

New and old approach spans (May 2008)

After more than a decade of study, construction began on a replacement for the cantilever portion of the bridge on January 29, 2002, with completion originally slated for 2007. The new eastern "signature" span was to feature a pair of side-by-side, five-lane concrete viaducts linking to a single-towered, self-supporting suspension span between the viaducts. If completed, this will become the largest bridge of this type. The approach viaducts from the eastern shore are currently being constructed just north of and parallel to the existing span. The grade of the new approach to the channel span is somewhat less than that of the present structure.

A price shock

The authorities were shocked when they opened the bids on the proposed tower portion, as there was only a single bid and it was considerably more expensive (US$1.4 billion) than their estimate ($780 million), partially because of a recent and unexpected rise both in the cost of steel and of concrete. As both concrete and structural steel are now commodities within the worldwide market, the prices were much higher than expected because of the current building boom throughout China. (China is currently consuming 40 percent of worldwide cement production.^{[citation needed]}) Another qualified potential bidder did not bid due to a number of construction uncertainties owing to the innovative design—another likely contribution to the very high bid. The entire project, which will require 100,000 tons of structural steel, is now expected to cost $6.2 billion (as of July 2005), up from a 1997 estimate of $1.1 billion (for a simple viaduct) and a March 2003 estimate of $2.6 billion that included a tower span.

Governor kills signature span

Six alternative eastern span proposals, December 10, 2004

On September 30, 2004, the office of Governor Arnold Schwarzenegger announced that without sufficient funds authorized by the legislature that the bid must be allowed to expire. It was at the time unclear if this would require a redesign to obtain a less expensive span. It might have been possible to quickly redesign the span using a more conventional cable stayed design, for which the construction methods and costs are well understood but the cost of the resultant delay was likely to far exceed any potential savings.

On December 10, 2004, the governor's office announced that the signature span concept had been scrapped, with the completion of the bridge to be by the construction of the simple viaduct originally proposed. The design, having gone full circle, remained expensive due to the continued high cost of materials. Many argued that there would be little difference in final cost with this lesser proposal since that concept required obtaining new permits, perhaps adding an additional two or three years; furthermore, a viaduct may not even be able to obtain Coast Guard approval since the maximum width of the ship channel would be reduced by almost half. Local reaction to this announcement was intense, with most suggesting that the bridge be built to appear as proposed — either in the steel material as bid or using a reinforced concrete span of similar appearance but of lower cost

Governor's economic analysis questioned

The standpoint of pro-"signature bridge" activists and regional politicians was reinforced by a legislative analyst's report in late January 2005.^[3] The report indicated, due to additional time delays and all new permitting requirements, that the governor's skyway proposal could likely cost additional funding and take longer to complete than the proposed signature span. This view was reinforced by a further report in March 2005^[4] indicating that the delay imposed by the governor had already added at least $100 million to the expected cost, subsequently refined to $83 million in a December 2005 report. Some of the temporary foundation structures for the main span had been removed and subsequently had to be replaced, in addition to inflation of costs over time.

To be built as designed

Between the two new viaducts to the span (under construction)

Construction progress, January 2007

The design controversy continued for over six months. In essence, the governor believed that the entire state should not share in the costs of building the bridge, as he considered it to be a local (Bay Area) problem. Northern Californians pointed out that when the southern portions of the state experienced disasters, the state supported rebuilding, especially as seen in earthquake rebuilding of freeways and the subsequent seismic retrofit of state freeway structures and bridges. Since the objective of the replacement of the eastern span is to prevent the necessity of complete rebuilding after a large earthquake the Bay Area residents felt justified in their call for state support.

A compromise was announced on June 24, 2005 by Governor Schwarzenegger. The governor said that he and State Senate President Pro Tempore Don Perata reached agreement to resurrect plans for the signature span. Cost estimates of the contract deferral expenses and inflation range attributable to the delay have ranged up to $400 million. Direct costs due to cessation of work (which included some dismantling of temporary structures and its recent restart) were determined in late 2005 to be $85 million.

After being approved by the Legislature, the compromise legislation was signed by the governor on July 18, 2005. The compromise calls for the state to contribute $630 million to help cover the $3.6 billion in cost overruns, and bridge tolls will be raised to $4 starting in 2007. At the time of the signing, the skyway portion of the bridge was 75 percent complete and the state was beginning to prepare to put the suspension span out for new bids.

The entire project is scheduled to be completed in 2013 at an estimated cost of $6.3 billion. In January 2006, costs for the main structure steelwork were determined to be $400 million in excess of these expectations.

New bids for the main span were opened on March 22, 2006, with two submissions at 1.43 and 1.6 billion USD. Owing to reserves built up with a $3.00 toll during the delay it was initially suggested by authorities that additional tolls exceeding $4.00 would not be required but due to added costs in other portions due to the delay and the cost of restarting the main span foundation work, an eventual toll of $5.00 is now expected. (The toll is only collected in the westbound direction.) The low bid by a joint venture of American Bridge and Fluor Corp. was accepted on April 19, 2006.

Weld controversy

On April 6, 2005, the FBI announced an investigation into charges by fifteen former welders and inspectors on the new eastern span that welders were rushed to an extent affecting their performance on up to one third of the welds and that workers were ordered to cover up defective welds by re-welding in a superficial manner. Many of these welds were now embedded in concrete, some deeply underwater.

A Caltrans spokesperson quickly responded^[5] with a public assertion that it was not possible that defective welds could be hidden from Caltrans inspectors. This assertion was subsequently tested by radiological, ultrasonic and microscopic inspection of some of the welds that were accessible yet alleged to be deficient. On April 21, 2005 news reports^[6] indicated that the Federal Highway Administration hired private inspectors to remove 300 pound (136 kg) sections for detailed laboratory analysis.

On May 4, 2005 local radio reported that the Federal Highway Administration said the tests by three independent contractors showed that welds pulled from three 500 pound steel chunks of the bridge "either met or exceeded required specifications."^[7][8]

• From a consultant (Mays) "The overall weld quality is excellent and greatly surpasses typical field welding quality that we have seen on similar structures."^[9]

• From a consultant (Teal) "...I found that most welds, although incomplete at many locations, generally conformed to the quality requirements of ANSI/AASHTO/AWS D1.5-96, and therefore conformed to the quality requirements of the Contract documents." ^[10]

• From a consultant (Fisher) "The weld quality provided in the steel footing boxes for the connection of the steel piles to the pile sleeves was found to be very good. The QA/QC provided by this project equals or exceeds that required by most states."^[11]

Since some of the material removed for inspection was specifically identified by the welders' complaints as worthy of inspection, this finding was received as very good news.^[12]

Recent progress

The first section of the new East Span, the 300-foot (91 m) span connecting the main cantilever section to the Yerba Buena Island Tunnel, was put into service on September 3, 2007. Construction of the new connector span started in early 2007 alongside the existing span. Caltrans closed the Bay Bridge during the Labor Day weekend so crews could demolish the old span. Once the old section was removed the new span was rolled into place using a computer-guided system of hydraulic jacks and rollers. The new section was secured into place and the bridge re-opened eleven hours ahead of schedule for the morning commute on the Tuesday (September 4, 2007) following the weekend.^[13][14] By November 2008, the principal task was to raise seven reinforced concrete pylons and a truss bridge to support the main span deck during its construction. This falsework will be removed after the completion of the supporting cable system.^[15]

By late August 2009 the temporary pylon work was complete and truss spans were in place. By mid-2009 the final connection of the viaduct portion with ground level at the eastern end was undergoing completion and the pedestrian walkway was being attached to the completed sections.

September 29, 2009: New S connector with traffic, white section replaced translated original segment to its left, remainder of original section is partially dismantled, to be replaced with a permanent transition structure to the new bridge. Viewpoint is near the U.S. Coast Guard harbor control center above the Yerba Buena tunnel

S-curve and related accidents

New temporary steelwork to route traffic around the location of the final approaches to the new bridge is in place and its connections to the tunnel exit and the existing bridge were completed in September 2009 during a single holiday closure, much as was done in September 2007. This bypass enables the construction of the permanent transition structure between the double-deck tunnel exit and the new side-by-side bridge structure. Upon completion of the bridge another extended closure will allow the removal of the temporary structure and the completion of the road link. The site has become well-known for accidents, from fender-benders to a fatal plunge.^[16] Mostly wrecks occur during non-commute time, when traffic flows faster, at or above the general bridge limit of 50 mph. Additional signage and visual and physical indicators indicating the 40 mph S-curve speed limit are planned.^[17]

• Pictures of construction of the S-curve, September 2009
• Pictures and diagrams of the S-curve, November 2009

September 2009 - Eyebar crack found

An inspection during the September 2009 work revealed a crack in a critical eyebar component of the main eastern span.^[18] Found in one of eight bars sharing the same load, the crack was not present two years earlier. Discovery of this crack by itself would likely have caused an immediate bridge closure, so the timing was fortuitous. Additional components to distribute the load around the crack were promptly designed and fabricated overnight, arriving by charter air from Arizona. The repair was completed ahead of schedule and the bridge was reopened a day before the original estimate, resulting in only minimal impact to typical area traffic. ^[19]

October 2009 - eyebar repair failure and bridge closure

On October 27, 2009, during the evening commute, parts of the September emergency repair, a crossbar and two tension rods, collapsed onto the upper deck roadway. One car and a delivery truck were struck or hit the 2.25 tons of debris. The bridge was closed to traffic in both directions for six days, reopening on November 2, 2009.

The failure of the repair was caused by two design defects: first, the tie rods closely fit the holes in the cross pieces over the saddles and second, wind caused vibrations in the rods, which in turn caused wear and bending at the through holes, eventually causing a rod fracture. The catastrophic dropping of the cross piece was caused by a lack of structural attachment to the saddle, being retained only by tack welds, friction and the tension of the tie rods. The rework of the design planned to include six significant modifications:

1. Structural welding of the cross pieces to the saddles to prevent catastrophic disassembly
2. Enlargement of the through holes to eliminate contact with the tie rods
3. Addition of a spherical seat and matching tie rod tensioning nut to reduce concentrated bending loads at the nut
4. Addition of tie rod cross ties between the rods and the eyebar at three locations to reduce wind induced vibrations and to secure the rods from falling in case of failure.
5. Installation of protective sleeves to prevent direct contact of tension rods where they cross other structural members
6. Addition of strain gauges and associated instrumentation to continuously monitor component loading

Proper fitting had proved difficult, requiring the disassembly of the new components to gain access for rework.

• Detailed diagrams of the repair scheme
• An overview of the repair process

Eastern span naming proposal

On December 14, 2004, the San Francisco Board of Supervisors, in honor of Joshua A. Norton, passed a resolution 8–2 (1 absent), file number 041618, "urging the California Department of Transportation and members of the California Assembly and Senate to name the new additions to the San Francisco Bay Bridge in honor of Emperor Norton I, Emperor of the United States and Protector of Mexico."^[20]

The proposal, however, needs the approval of the city of Oakland and then state authorities to be ratified. The Oakland City Council has yet to consider the resolution. Since most of the new span is in Oakland, and Emperor Norton was a San Franciscan, members of the council have expressed disdain for the proposal.^[21]

References

External links

Wikimedia Commons has media related to: Eastern span replacement of the San Francisco – Oakland Bay Bridge

• Bay Bridge Project official website
• San Francisco-Oakland Bay Bridge East Span Seismic Safety Project
• "A Bridge Too Weak?" SF Weekly article on engineering concerns about the self-anchored main span design
• Caltrans Alternatives report December 10, 2004 (PDF)
• "Emperor Norton's name may yet span the bay" San Francisco Gate story on renaming the bridge
• "TOWERING QUESTION -- WILL IT FINALLY BE BUILT?" -- San Francisco Gate summary about the construction delays
• "The Bridge So Far – A Suspense Story" a 2006 documentary film chronicling the delays in construction
• Metropolitan Transportation Commission (MTC) timeline

• Eastern span replacement of the San Francisco – Oakland Bay Bridge is at coordinates 37°49′00″N 122°21′07″W / 37.8168°N 122.3519°W / 37.8168; -122.3519 (Eastern span replacement of the San Francisco – Oakland Bay Bridge)Coordinates: 37°49′00″N 122°21′07″W / 37.8168°N 122.3519°W / 37.8168; -122.3519 (Eastern span replacement of the San Francisco – Oakland Bay Bridge)