Eastern span replacement of the San Francisco-Oakland Bay Bridge
From Wikipedia, the free encyclopedia
  |
This article or section contains information about a future bridge, which is under construction. It may contain information of a speculative nature and the content may change dramatically as the construction completed, and more information becomes available on it. |
As of June 2006, work is continuing on the eastern span replacement of the San Francisco-Oakland Bay Bridge. The bridge is currently scheduled to open to traffic in 2013. [1]. The bridge, built in the early 1930s, became the subject of concern after a section collapsed during the October 17, 1989, Loma Prieta earthquake.
[edit] Earthquake damage
During the 1989 Loma Prieta earthquake, which measured 7.1 on the Richter scale, a 50-foot section of the upper deck of the eastern truss portion of the bridge collapsed onto the deck below, indirectly causing one death (actually due to misdirection of traffic by the California Highway Patrol). The bridge was closed for a month and one day as construction crews repaired the fallen section. It reopened on November 18th of that year.
Given the distance to the epicenter of the Loma Prieta (roughly 70 miles 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 infamous San Andreas and the lesser-known but far more dangerous Hayward) would destroy the major cantilever span. Like most expensive-to-solve potential problems, there was no political will to act. The Loma Prieta earthquake was the proverbial "wakeup call" for all concerned. 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.
[edit] 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 US. dollars. The overall appearance would be little changed.
[edit] Initial replacement proposal
Engineering and economic analysis in 1999 suggested that a simple replacement bridge would cost only 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 the politicians, being characterized as a "freeway on stilts".
[edit] Signature span proposals and selection
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.
Some believe this is a serious conflict of interest, as members of the Engineering and Design Advisory Panel (EDAP) who were selecting the bridge design also had bridge proposals under review. In fact, three members of the EDAP reviewed and commented on the design submitted by their own firm or by a team that they were a member of. All of this information is in public domain and can easily be checked by any investigative body.
[edit] Construction begins
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 would have 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.
[edit] 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$1,400,000,000) than their estimate ($780,000,000), partially due to a recent and unexpected rise both in the cost of steel and of concrete. As both concrete and structural steel are now commodities within a world wide market the prices were much higher than expected due to the current building boom throughout China. (China is currently consuming 40 percent of worldwide cement production.) Another qualified potential bidder did not bid owing 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.
[edit] Governor kills signature span
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 spar of similar appearance but of lower cost.
[edit] 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. This 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 indicating that the delay imposed by the Governor had already added at least one hundred million dollars to the expected cost, subsequently refined to 83 million dollars in a December 2005 report. Some of the temporary foundation structures for the main span had been removed and had to subsequently be replaced, in addition to inflation of costs over time.
[edit] 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. As many of these welds were now embedded in concrete, some deeply underwater, this brought a shock to the entire Bay Area.
A Caltrans spokesperson quickly responded[2] 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[3] 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."
From a consultant (Mays) "The overall weld quality is excellent and greatly surpasses typical field welding quality that we have seen on similar structures."
Since some of the material removed for inspection was specifically identified by the complaints as worthy of inspection, this finding was received as very good news.
[edit] To be built as designed
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 24 June 2005 by Governor Schwarzenegger. The Governor said that he and State Senate President Pro Tem 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 four hundred million dollars. 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 138 million dollars.
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 2012 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. A toll of five dollars was expected to be quite probable once the final price was determined. Compared to other major bridges this is not particularly high, considering that the single toll allows a round trip.
New bids for the main span were opened on March 22, 2006, with two submissions at 1.43 and 1.6 billion USD, the lower of the bid being generally considered a bargain. 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 low bid by a joint venture of American Bridge and Fluor Corp. was accepted on April 19th, 2006.
[edit] Some history of the eastern span
This eastern portion of the bridge has an interesting history. It has long been thought by East Bay residents that Oakland got the ugly bridge while San Francisco got the pretty one. The original Caltrans replacement design was for a simple parallel lane viaduct (resembling portions of a freeway which could be found anywhere), and which was considered to be another insult to the East Bay residents and commuters. There was much political bickering over whether the bridge should be built to the north or to the south of the existing bridge, with the "Mayors Brown" (San Francisco's Willie Brown and Oakland's Jerry Brown) on opposite sides of the issue. This argument may have caused up to a two year delay and billions of dollars in additional costs. While a number of proposals were submitted for a "signature" bridge, and the design chosen is considered by most critics to be acceptable from an aesthetic viewpoint, many questions have been raised by engineering experts as to its survivability under various scenarios - both natural and otherwise. The proposed tower is a self-supporting suspension bridge without cable anchorages. What is amazing is that an innovative design both beautiful and practical, produced by the architect Frank Lloyd Wright for another bay area location was not even considered. That design was for a "Butterfly" bridge intended to replace another span crossing the bay, the Hayward-San Mateo Bridge. There was a similar fight over the design of that bridge, with Caltrans initially proposing what was called by critics a "Rip Van Winkle" design, a two deck truss similar to the obsolete eastern span of the Bay Bridge or portions of the "roller coaster" Richmond-San Rafael Bridge.
[edit] Eastern span naming proposal
On Tuesday, 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. [4]
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 and members of the council have so far only expressed disdain for the proposal. [5]
[edit] External links
- Bay Bridge Project official website
- San Francisco-Oakland Bay Bridge East Span Seismic Safety Project
- A Bridge Too Weak?
- CalTrans site
- CalTrans Alternatives report December 10, 2004 PDF download (not a web page)
- San Francisco Gate story on renaming the bridge
- Pictures and info on the new bridge
- The Bridge So Far - A documentary chronicling the delays in construction
- Metropolitain Transportation Commission (MTC) timeline
- Maps and aerial photos
- Street map from Google Maps, or Yahoo! Maps, or Windows Live Local
- Satellite image from Google Maps, Windows Live Local, WikiMapia
- Topographic map from TopoZone
- Aerial image or topographic map from TerraServer-USA
