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Vorlage:Importartikel/Wartung-2013-04

Der Ersatzbau für den Ostteil der Bay Bridgezwischen Oakland und San Francisco befindet sich seit 2002 im Bau und soll am Labor Day 2013[1] eröffnet werden. Die Baukosten werden etwa $6.3 Millarden US Dollar betragen.[2]

Die Bay Bridge besteht aus zwei Teilen. Der Westteil besteht aus mehreren Hängebrücken und führt bis Yerba Buena Island(YBI). Der Ostteil bis Oakland besteht aus verschiedenen Fachwerkbrückensegmenten. Dieser Ostteil wurde als risikobehaftet eingetuft nach dem beim Loma-Prieta-Erdbeben 1989 ein Segment einstürzte. Der Ersatzbau soll dem stärksten zu erwartenden Beben innerhalb von 1500 Jahren standhalten können und eine Lebensdauer von mindestens 150 Jahren haben.[3]

Der Turm der selbstverankerte Hängebrücke wurde 2011 fertiggestellt. Die Last der gesammten im Sommer 2012 fertigestellten Konstruktion wurde am 20. November 2012 auf die Seile übertragen. Seit dem ist die Brücke die längste selbverankerte Hängebrücke der Welt.[4]

Seit März 2013 sind die Anschlüsse auf beiden Seiten und damit die gesammte Fahrbahn bis auf Asphaltierungsarbeiten fertiggestellt.[5] Jedoch wurde Mitte März festgestellt das eine hohe Zahl von Verankerungsschrauben bereits beim Befestigen versagen im April 2013 war noch nicht klar ob die das Eröffnungsdatum erneut verzögert.

Inhaltsverzeichnis

Vorgeschichte[Bearbeiten]

<--===Seismic hazard=== It has been widely known that the eastern span was likely to collapse in a major earthquake. Other than amongst users of the bridge there was little interest in addressing the problem, either locally or within the California Department of Transportation ("Caltrans"), with most Caltrans seismic retrofit work before the 1989 Loma Prieta earthquake being done in response to the 1971 San Fernando earthquake, which exposed the vulnerability of freeway overpass structures. Vorlage:Wide image-->

Loma Prieta Erdbeben[Bearbeiten]

Eingestürztes Segment der Bay Bridge nach dem Loma Prieta Erdbeben 1989

Während des Loma Prieta Erbebens 1989, welches 6.9 auf der Moment Magnituden Skala erreicht, brach ein 15 m lange Stück des Oberdecks der Brücke zusammen. Eine Person wurde in Folge des Einsturzes getötet.[6][7] Bereits nach einem Monat am 19 November 1989 wurde die Brück nach den Reparaturarbeiten wieder für den Verkehr freigegeben. Als Ursache für den Einsturz wurde die der Übergang zwischen zwei verschieden Baustilen an dieser stelle bestimmt welches ein stark unterschiedliches Kraftaufnahmevermögen erzeugte. Analysen ergaben das bei einem nur wenig stärkeren Beben eine der beiden Strukturen Komplett aus der Verankerung gerissen worden wäre.


2003–2032 large event probability chart

Es wurde Offenbar das die Ostseite der Baybrigde Erdbebensicherer werden muss.

Schätzungen von 1999 gaben die Chance für ein starkes Beben in der gegend mit 70% an. Studien von 2004 hingegen 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; a more recent (2008) analysis asserts an increased probability of a major event on the Hayward Fault.[8]

In addition to the replacement of the eastern span, the damage motivated engineering examination of the bridge's western approaches, as well as portions of the Golden Gate Bridge, Bay Area Rapid Transit, and other public structures throughout the Bay Area, and many have been reinforced, isolated and/or replaced in whole or part.

Design proposals[Bearbeiten]

Initial retrofit and replacement proposals[Bearbeiten]

To be retrofitted[Bearbeiten]

The initial proposal for the eastern span involved the construction of substantial concrete columns to replace or supplement the existing supports. There would also be modifications to the lattice beams as is now complete for the western suspension spans. 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. The robustness of a retrofit was called into question directly by the Army Corps of Engineers in a highly critical report[9] and indirectly by the collapse of a retrofitted overpass in the 1994 Northridge earthquake in Los Angeles, that structure having been modified in response to the Sylmar Earthquake 23 years prior.[10]

To be replaced[Bearbeiten]

Artist's rendering of the basic viaduct-style span, also known as the "Skyway" design (1997)

Engineering and economic analysis in 1996 suggested that a replacement bridge would cost a few hundred million dollars more than a retrofit of the existing eastern span, 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 an elevated viaduct consisting of reinforced concrete columns and precast concrete segment spans as seen in the illustration at right. The design criterion was that the new bridge should survive an 8.5 magnitude earthquake on any of several faults in the region, but particularly the nearby San Andreas and Hayward faults. The aesthetics of the proposal were not received well by either the public or their politicians, being characterized as a "freeway on stilts".[11]

Signature span proposals and selection[Bearbeiten]

Original and final eastern span "signature" bridge 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 (an example[12]) 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 EDAP who were selecting the bridge design reviewed proposals by their own firms and rejected all proposals that did not have a representative on the EDAP.[13][14] The design chosen is more expensive than the alternatives, because the primary structure cannot be self-supporting until it is structurally complete. This requires the building of two bridges, the first a falsework to support the final span, which must be removed upon completion. It has also been criticized as both a less structurally robust design and with less predictable construction costs than other modern spans.

Alignment controversy[Bearbeiten]

In 1997, 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. Yerba Buena Island is within the city limits of San Francisco and the proposed (and current) northern alignment will cast a shadow over certain prime development sites on the island's eastern shore. Even the US Navy (at the time the controlling authority of the island) was involved at the behest of San Francisco in restricting Caltrans soil engineer's access to the proposed site and that delay may have caused up to a two-year delay and many hundred millions of dollars in additional costs.[15][16]

Signature span grade and location alternatives[Bearbeiten]

Various options were determined to be worthy of consideration and were carefully examined jointly by state and federal authorities, with input from the United States Coast Guard.[17]

Grade alternatives included:

  • Extending the sea level approach grade westward, with a steep approach to the span.
  • Using a relatively constant grade, including on a portion of the span.
  • Using a relatively constant grade to near the span, with the span level.

The last alternative was chosen as having a superior visual effect and improved driving experience. The grade of the new approach to the channel span is somewhat less than that of the present structure and less ship clearance is provided under the span owing mostly to the depth of the deck box structures.

Alignment alternatives included:

  • S4: a southern alignment, slightly curved, but a shorter route than the northern alternatives.
  • N2: a two-bend northern alignment close to the existing bridge.
  • N6: a single bend alignment, with the main span tending northward to the curve to the eastern approach viaducts, those being parallel to the existing double-deck truss causeway approach.

The last alternative was selected, as it presents a superior view of San Francisco to the west compared to the others where views are obscured by Yerba Buena Island. Any more northerly track would encounter more difficult geotechnical circumstances.

History[Bearbeiten]

Offshore fabrication of components[Bearbeiten]

Even though controversial, authorities decided to allow bids to include major components and materials not made in the United States.[18] This was partly due to the cost of materials, but more substantially, required by the lack of suitable fabrication facilities within the United States, or even within the western hemisphere. Since such facilities would have to be built new and the prospects of additional work (at that time) would be either low or uncertain, the cost of fabrication would be much higher due to the facilities cost being supported by a single job. As acceptance of Federal Highway funds generally comes with "Made in America" restrictions, the bridge is being built without such funds, for which it would otherwise qualify owing to its carriage of Interstate 80. In contrast, China has low cost materials producers and major fabricators of bridge components, due to the current and extensive investment in infrastructure being made by its government. The Chinese facilities producing the SAS deck components were built new, with the speculative expectation that further work, both in China and abroad, would allow the extensive capital costs to be amortized over several subsequent projects. Other major components have been produced in Japan (not known as a low cost producer), owing to the availability of large steel casting, welding, and machining capabilities. Suspender saddles come from England. A spokesman for the joint venture claimed the United States (in both private and public spheres) has neglected to make such investments for a long time and has as a consequence lost the ability to make suitably large steel components for civil structures such as this bridge.[19]

Some components are made in the USA, and these include fabrication of offshore spooled wire into parallel wire strands for the main cable, some large bolts and fittings, the wire rope suspender cables, lighting poles, lighting fixtures, and LED bulbs.

Construction begins[Bearbeiten]

Construction on the skyway in progress at left, with main span counterweight support columns in place at right of center (2004)

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 will feature a pair of side-by-side, five-lane concrete viaducts linked to a single-towered, self-anchored suspension span ("SAS"), and a transition structure joining the SAS to the existing double-deck tunnel. When completed, this will become the largest bridge of this type, and will also have some unique features. The approach viaducts from the eastern shore are largely complete and located just north of and parallel to the existing truss viaduct.

Construction is delayed[Bearbeiten]

A price shock[Bearbeiten]

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 rise in the cost of steel and concrete. As both concrete and structural steel are now commodities within the worldwide market, the prices were much higher than expected because of a concurrent building boom throughout China. (China was then consuming 40 percent of worldwide cement production.[20]) Another qualified potential bidder did not bid due to 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 terminates signature span[Bearbeiten]

On September 30, 2004, the office of Governor Arnold Schwarzenegger announced that, without sufficient funds authorized by the legislature, 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 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 tower of similar appearance but of lower cost.

Governor's economic analysis questioned[Bearbeiten]

The standpoint of pro-"signature bridge" activists and regional politicians was reinforced by a legislative analyst's report in late January 2005.[21] 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[22] 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.

To be built as designed[Bearbeiten]

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, 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 had 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 included some dismantling of temporary structures and their reconstruction upon the subsequent restart.

After being approved by the legislature, the compromise legislation was signed by the governor on July 18, 2005.[23] 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, not counting the demolition of the old span.

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[Bearbeiten]

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[24] 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[25] 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."[26][27]

  • From a consultant (Mays) "The overall weld quality is excellent and greatly surpasses typical field welding quality that we have seen on similar structures."[28]
  • 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."[29]
  • 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."[30]

Since some of the material removed for inspection was specifically identified by the welders' complaints as worthy of inspection, this finding was received as good news.[31]

Eyebar crack, repair, subsequent failure and bridge closure[Bearbeiten]

An inspection during a construction-related closure in September 2009 revealed a crack in a critical eyebar component of the existing main eastern span.[32] 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 fortunate. 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 traffic.[33]

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 by or collided with 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 included 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.

A more permanent repair was made in December 2009. The bridge remained open to traffic while crews cut away the cracked end of the eyebar and spliced a new end to the undamaged part of the eyebar with a pair of gusset plates. The repaired eyebar was placed under tension and the temporary block and tie rod assemblies were removed.[34][35]

Potential for foundation flaws due to alleged irregularities in inspection[Bearbeiten]

In early November 2011, The Sacramento Bee newspaper reported and analyzed various reports (including "whistle-blower" statements) concerning the potential for falsified inspection reports associated with deep pile foundations, some supporting the SAS main tower, and others associated with other projects not associated with the eastern span.[36] That article, and a later Sacramento Bee article, published on May 26, 2012, provided details about construction and testing concerns and quoted experts in relevant engineering fields who raised questions about the adequacy of Caltrans’ testing and oversight, and construction and testing practices of the bridge builder.[37] On June 12, 2012, shortly after publicly supporting further study of the concerns raised in the May Bee article,[38] Caltrans issued a press release with an attached letter to the Bee's Executive Editor from Caltrans Director Malcolm Dogherty. That letter included a request for a full retraction of the article, this after asserting a number of specific technical refutations and criticisms of the language and tone of the article.[39] On June 24, 2012, Joyce Terhaar, the Executive Editor of the Bee, responded in defense of the article and the mission of the paper.[40]

Caltrans has also responded with a nearly one-hour video presentation, viewable at baybridgeinfo.org.

On August 4, 2012, The Bee reported on a study in progress by Caltrans engineers, who are examining foundation testing for the agency. That team of engineers, called the "GamDat" team by Caltrans, found new evidence of questionable data associated with tests the tower foundation.[41] Following that Bee article, the California Senate Transportation Committee asked the state Legislative Analyst’s Office to convene a panel of independent experts to examine concerns about the SAS tower foundation, and to report on its findings.[42] That report is expected to be released in by the Spring of 2013. Caltrans has stated that it expects to open the bridge by Labor Day 2013, assuming that questions associated with the tower foundation do not affect that schedule.

Bolts fail upon load test (March 2013)[Bearbeiten]

Three inch (7.5 cm) diameter bolts connect portions of the bridge deck mounting bosses to several concrete columns. There are 288 such bolts of various lengths. The bolts are tested in place by overtightening their retaining nuts. In the two weeks subsequent to this tightening, 30 of the bolts first 96 bolts loaded have failed.[43] These bolts, (made by a vendor in the USA) vary in length form 9 to 17 feet and failure has initially been attributed to hydrogen embrittlement, with hydrogen introduced during either manufacturing or electroplating. Some of the bolts can be replaced while others cannot be removed and load transfer will require more complex remediation methods. Repairs are not expected to delay the opening but could cost up to five million dollars ($5,000,000).[44]

Eastern span naming proposal rejected (December 2004)[Bearbeiten]

Emperor Norton I

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.",[45] According to the Oakland City Council, the naming of the new San Francisco Oakland Bridge was rejected and will it not be named after Joshua A. Norton.[46]

Golden State Warriors Logo (June 2010)[Bearbeiten]

On June 17, 2010, the Golden State Warriors unveiled a new logo featuring the yet to be completed self anchored suspension span. The new logo was debuted in the 2010–11 season.[47]

Design and construction[Bearbeiten]

Eastern viaduct construction continues[Bearbeiten]

Eastern span of the Bay Bridge and replacement construction in the early morning hours (2007)

By 2007, 75 percent of the skyway portion was completed, which will connect the SAS portion of the bridge with the Oakland shore. As this section crosses the shallower portion of the bay, the foundations could be constructed within sheet-pile cofferdams. 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. A worker's drive-over of the completed skyway can be seen here.

Eastern viaduct column and footing design[Bearbeiten]

Cutaway illustration - battered piles support the skyway

Rather than set pilings deep enough to reach bedrock, the pilings are founded in firm archaic mud below the soft muds deposited by distant placer mining in the late 19th century. Since even the archaic mud is too weak in this concentrated load application for conventional vertical friction piles, large diameter tubular piles were driven (inside cofferdams) at angles, forming a "battered" (splayed) footing, through the archaic muds into the firm aggregated sand, mud, and gravel of the Alameda formation.[48] Where long pilings were needed segments would be welded together as completed segments were driven deep.

When all pilings were in place, a reinforced concrete pad was poured at the bottom of the cofferdam to form a footing for the column, subsequently cast in place around rebar using reusable metal formwork.

Eastern viaduct segmented assembly[Bearbeiten]

700-ton segment lift

A single viaduct segment located over each column was cast in place using forms.[49] Pairs of precast span segments, fabricated in Stockton, California, were barged to the location and lifted into place with a specialized cantilever lift. (Cantilever lifts, counterweights and other equipment and materials were lifted by a barge crane or by a jack-up crane located between each column pair.) Once in the proper location, the pair could then be joined with through tendons (cables within conduits that are tensioned with jacks), forming a balanced cantilever over the column. Eventually, the gap in spans between columns were closed, forming a tendon-reinforced beam.

Oakland Touchdown[Bearbeiten]

February 19, 2012: With the completion of a temporary eastbound (upper deck) bypass the new bridge's eastbound touchdown (center) can be completed

The Oakland Touchdown is a curved and elevated roadway that connects the skyway to the Oakland shore (the beginning of the bridge). The curve is required to bring the alignment to that of the existing ground-level approach road. Like the Yerba Buena Island Transition Structure ("YBITS") to the west of the main span, this section is also an end segment of the new bridge and is being constructed at the same pace as the YBITS. The construction process consists of two phases, the first phase already completed (westbound traffic side). The eastbound touchdown cannot be completed until the existing roadway is out of the way, this done by constructing gentle swing to the south so that the touchdown may be completed.[50][51] The first stage of this work was to move the eastbound traffic to the south was completed with only minor traffic delays during the 2011 Memorial Day holiday (May 28–30).[52] The driving experience has been improved, without the problems that came with the infamous S-curve.[53] A second stage to move the westbound traffic into the space made available required the construction of an elevated approach and this was completed on February 19, 2012 (seen in the illustration above).[54] This recently designed procedure is expected to save time in the total effort, speeding the completion of the span to a usable state.[55]

Holiday shutdown (February 17–19, 2012)[Bearbeiten]

On the three-day weekend beginning 8:00 PM Friday, the westbound lanes were shut down to allow the connection of the approach roadbed with the new temporary structure. The execution of this task was dependent upon weather, dry conditions being required for re-striping the lanes, and it was not determined until a few days before that the work would be done on this weekend. Originally scheduled for completion by 5 A.M. on Tuesday, February 21, the work was completed 34 hours ahead of schedule, and opened to traffic at approximately 7:15 P.M. on Sunday, February 19.[56]

With the completion of the re-routing, a portion of the double deck truss structure may now be removed at that location to allow the construction of the new span's eastbound touchdown.

Main span design[Bearbeiten]

The principal span is of a seldom-built type, being a self-anchored suspension (SAS). It is unique in being both single tower and asymmetrical, a design tailored to the site. For ship channel clearance, the bridge would require at least one long span, while ready access to bedrock was found only close to Yerba Buena Island. A two tower cable-stayed design would require very deep tower footings, and a conventional two tower suspension bridge would additionally require a massive anchor to be built in deep bay mud. The curved nature of the approach places additional constraints upon the design. Construction progress of the main span is shown here (Bay Bridge Info).

While earlier bridges of this type use chain eyebars, the long span needed here uses wire cable as do other modern suspension bridges, but uniquely, this is a single loop of cable rather than the usual pair of cables and, rather than being spun in place above the catwalks, substantial bundles of strands are dragged into place with temporary support above the catwalks, to be finally suspended by tensioning of the strand. These strand bundles are then arranged to be finally compacted to form the completed main cable.

July 31, 2009: First eastern main span support with partial truss falsework beyond

Being asymmetrical, the shorter western span must be pulled down against the forces imposed by the longer eastern span. In order to avoid uplift in the supporting columns, the span is terminated with a massive concrete end weight, initially supported solely by the columns. This end weight also carries the turning saddles for the main cables. As seen in the northwest corner image above, there is an upward component to the tension force provided by the main cable, and it is this component that removes most of the weight of the end cap from its columns. (The greater, horizontal, component is countered by the compressive forces exerted by the box deck structure as is characteristic of this type of bridge.)

The segments of each of the two deck spans will be retained in compression during a severe earthquake by post-tensioned internal tendons joining the extreme end caps, these carried internally in cable trays. These tendons are required since the eastern end support is both much lighter than the western counterweight and the soil conditions are radically different at each end, the western end being founded in bedrock shale while the eastern end, with vertical supports driven to bedrock, is mostly contained with softer mud deposits; deposits which respond much more actively to seismic shocks than does the shale. The intent is that the combination of the tensioned tendons and the compressive roadbed box structure will keep the two end caps in the same relative position.

The bridge segments at each end are not simple repetitions of the central span segments:

  • The extreme deck segments on the eastern end are curved and tilted to fair into the curved portion of the skyway. These extreme segments are also beyond the main cable strand anchors and the eastern support columns and a substantial portion of the bridge joining the skyway is already in place (the gray portion seen above).
  • The extreme east bound deck segments on the western end must fair with the horizontal eastbound portion of the YBITS connector, while the westbound (north side) segments begin a rise to the westbound YBITS, elevating traffic to the upper deck of the Yerba Buena tunnel.

S-curve construction[Bearbeiten]

The old cantilever bridge was connected to the Yerba Buena tunnel with a double-deck truss causeway that included a curved section. As this structure occupied an area that must be clear for the new bridge approach, it was necessary to construct an entirely new (yet temporary) approach to the old bridge. This was required to swing to the south to clear the area for new construction, and then back to the north with a more severe curve to connect to the cantilever. As there would only be a few days available during which the bridge could be shut to traffic, the curved portion was built adjacent to its final position on a trestle that extended beneath and beyond the old curved connector. During replacement, the old section was jacked out of the way (to the north), and the new section jacked into place.

On September 3, 2007, the first section associated with the construction of the new East Span, the Vorlage:Convert temporary span connecting the main cantilever section to the Yerba Buena Island Tunnel, was put into service. 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 remove 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 11 hours ahead of schedule for the morning commute on the Tuesday (September 4, 2007) following the weekend.[57][58] On September 2009 during a single holiday closure, 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, 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.

All of the section of the old span over Yerba Buena Island (around which the S-curve routes traffic) has been dismantled, and supports for the new span are currently being built in that location.[59]

The S-curve site has become well known for accidents, from fender-benders to a fatal plunge.[60] 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 were installed following the major accident.[61] The upper deck speed advisory at the curve has been posted as 35 mph and an improved system of "rumble strips" has been installed.[62][63]

SAS falsework[Bearbeiten]

Falsework parallel truss bridges temporarily supporting deck segment box structures

The entire multi-segment deck structure must be supported in precise alignment until:

  • The end caps with anchors and turning and tensioning saddles are complete.
  • The tower with its main cable saddle is complete.
  • All deck segments are in place and joined.
  • The internal tendons are placed and tensioned.
  • The main cable is spun.
  • All suspender cables are in place and adjusted for tension.
  • The main cable tension is balanced on each side. (This is maintained as the suspender cables are tensioned.)

The falsework to perform this task is a pair of substantial truss bridges, prefabricated in segments, with columns and span segments lifted into place by barge cranes. The trusses are supported on foundations consisting of or built atop deeply driven piles. Upon completion of the bridge, the entire falsework structure and all exposed underwater supports will be removed to make a safe channel for deep draft ships transiting to and from the Port of Oakland.

Deck placement[Bearbeiten]

Vorlage:Wide image

By late August 2009, the temporary column work was complete, truss spans were in place and prefabricated sections were being placed upon it.[64][65] A giant barge crane, the Left Coast Lifter, was used to emplace the 28 main deck box structures.[66] Major segment placement on the SAS section of the bridge was completed in early October 2011 and final welding is in progress.[67] On October 19, 2011, the small gap between the SAS deck and the curved skyway extension was finally closed for the east-bound side with the west-bound gap being closed the following week. By November 2011, the deck placement of the SAS span was finally complete, making 1½ miles of continuous roadway (non-stop without any gaps), starting from the Oakland Touchdown, across the skyway, onto the SAS and ending right up to the then-unfinished Yerba Buena Island Transition Structure.[68]

Main span tower[Bearbeiten]

Innovative tower design[Bearbeiten]

First stage tower segments showing cross section and attachment methods. The lower external gray areas will be covered by sacrificial box structures ("mechanical fuses"), while the upper are covered by external flat plates with numerous fasteners to join the segments.

The design employs extensive energy absorbing techniques to enable survivability and immediate access for emergency vehicles following a Maximum Creditable Earthquake (MCE), here estimated at 8.5 moment magnitude in a 1500-year time span. Rather than designing for rigidity, it is instead a flexible structure, with resonant motion absorbed by the plastic shear of sacrificial, replaceable components. Smaller earthquakes will impose mostly elastic stresses on components, with a higher proportion of plastic (and thus energy absorbing) stresses in larger earthquakes. This design philosophy extends to other metal components of the bridge, including the sacrificial tubular end keys that align the self-anchored suspension with its approach structures at each end.

The tower consists of four columns. Each roughly pentagonal column consists of four tapering and/or straight sections joined end-to-end by external plates and internal stringer finger joints secured with fasteners.[69] (Images of the lifting and joining methods may be seen here.) The columns are also joined horizontally by sacrificial box structures. These box joins are intended to absorb earthquake-induced motion by elastic and plastic shear deformation as the tower sways. Under a severe earthquake, this deformation absorbs energy that could otherwise lead to destructive tower motion, thus protecting the primary structure of the span. It is expected that this design will allow the immediate use of the bridge for emergency vehicles, with the joins being replaced as needed to restore the bridge to its original condition.[70] Uniquely, the tower has no direct connection to the roadbeds, with enough space to allow swaying under severe earthquakes without collision.

The tower also has an unusual appearance at certain daylight lighting angles. Near sunrise and sunset, multiple illuminations from the bright white paint can cause a subtle glow to appear from the tower's interior surfaces, depending on the season. Other effects will appear more consistently at night from electric lighting.

Tower erection[Bearbeiten]

March 4, 2011: Phase 4 with all four columns in place; the jack-up crane (to the left) is used to erect the scaffold, and a gantry crane atop the scaffold lifts and places the tower columns.

In order to build the SAS tower, the process consists of five phases; the first four phases each having four columns lifted and bolted into place, while the last phase is to lift the final top cap that will carry the crowning main cable saddle. On July 28, 2010, the first of four below-deck main tower pillars were erected, the four having arrived earlier in the month by barge from China.[71] They were placed by lifting one end from a barge into a temporary erection scaffold, with a carriage on the barge to allow the lower end to move into place. Illustrations of the process can be found here (SFGate.com) After the columns were bolted into place and the first phase was complete, the scaffolding was then extended upward to allow the next set of above deck columns to be erected, lifted, and translated into position, a process repeated for each of the first four phases.[72][73]

Tower erection continued when the second set of columns finally arrived on the week of October 24, almost three months after the first set were placed. The second set of columns were erected by a gantry atop the scaffold and were placed over the first four columns that were placed earlier in the year. After the columns were set into place, they were bolted together with the first set of columns. After this second phase was complete, the tower was now about 51 percent completed and stood at a height of 272 feet. The third set of tower columns did not arrive until the week of December 15, but it was still early enough to have the third phase completed before the holidays. The third set, now with a larger crane, were lifted and placed over the second set of columns. The tower now stood at an impressive height of 374 feet and was 71 percent complete.[74] The erection process did not continue until the following year when the final set of tower columns finally arrived by Valentine's Day 2011. These four columns, each being 105.6 feet tall, were lifted on the week of February 28 and placed over the third set of columns. The tower now stood at a height of 480 feet and was now 91 percent complete.[75]

April 15, 2011: The grillage is now in place.

The fifth and final tower phase was to lift a grillage that weighs about 500 tons, lift the main 450-ton cable saddle, and finally lift the final tower head which will complete the entire SAS tower. All of these final pieces arrived at the site the same day the fourth set of tower columns arrived. On April 15, the first part of the fifth and final phase was initiated. The 500-ton grillage was lifted 500 feet in the air and was placed over the fourth set of columns. The tower then stood at a height of 495 feet and is now 94 percent complete. It took about one day to lift and place the grillage on top of the tower.[76]

Crowning double cable saddle emplacement[Bearbeiten]

May 19, 2011: Near sunset, the cable saddle is being positioned before final touchdown.

Working the entire day of May 19, 2011, operating engineers and ironworkers lifted and emplaced the 900,000 pound double cable saddle atop the SAS tower. While a large portion of the span was fabricated in China, this particular piece came from Japan, as do the eastern and western deviation saddles and main cable hydraulic jacking saddle. (Component fabrication images may be seen here.) At least twenty workers, engineers, and reporters stood high atop the scaffold to observe and record the lift, some seen here departing via the stairs on the right.

This cable saddle will guide and support the mile-long main cable over the tower, and as of December 2011, the deck placement of the SAS span is complete and the cable construction is in progress. In July, the tower head was lifted and placed over the saddle in a test fitting and was then removed to allow the laying of the cable. Once the cables are placed and are anchored throughout the whole SAS span, the tower head will then be permanently installed, along with aircraft warning beacons. The entire SAS tower will then be completed at a final height of Vorlage:Convert.[77] Vorlage:Clear

SAS main suspension cable[Bearbeiten]

(Some of the tasks described here are not yet complete)
Test section of the SAS cable; Distinct colors mark individual parallel wire strands, each a bundle of 127 pencil-thin wires. There are 137 such bundles, each individually terminated at the eastern end of the SAS.

The tower saddle includes eyebars for the attachment of temporary cables that support four walkways, each a simple suspension bridge (called a catwalk) that allows access to the cable spinning mechanism and the main cable. In several ways similar to a ski lift, additional superior cables will carry one or more of these travelers, wheeled devices that shuttle from one end of the span to the other, pulled by drafting cables manipulated by several winches.

June 24, 2011: The gantry crane has been removed and two of the four temporary catwalks have been installed.

The main span use a single cable, spun using pre-bundled groups of wires as follows:[78]

  • From an anchor point at the eastern end of the main span.
  • Across an eastern corner horizontal deviation saddle.
  • Over a vertical deviation saddle on the eastern end.
  • Upward and over the corresponding half of the main tower saddle.
  • Down to a 90-degree deviation saddle at the western counterweight.
  • Across the counterweight, passing over the hydraulic tensioning saddle.
  • Around the opposing western deviation saddle.
  • Upward to the other half of the main tower saddle.
  • Over an eastern vertical deviation saddle.
  • Down to the final eastern corner deviation saddle.
  • To the appropriate anchor point in the eastern strand anchor opposite the beginning.

As a bundle is laid down, it was initially supported by supports mounted on the catwalk, then both ends were attached and the cable is tensioned at the eastern anchor points. As with a conventional cable suspension span, all of the tensioned bundles were then compressed into a circular shape and protected with a circular wrap of wire. Saddles for suspender cables are currently being added and suspender cables placed and tensioned. The suspender cable tensioning will eventually lift the span from its supporting falsework[79]

October 1, 2011: Tracks within the blue cage will guide the strand hauler around the deviation saddle and continue across the jacking saddle and around the opposite deviation saddle.

In mid-June 2011, preparations for the spinning of the main cable began by installing the temporary catwalks on the SAS span. Both western catwalks were installed and by mid-August, all four catwalks were installed in place and an approximation of the completed outline of the bridge could then be seen. All four catwalks, the traveler, its suspension cable and the drafting cables and the winches and specialize tracks at the deviation saddles must be in place before cable spinning can begin. These catwalks are required for worker's access to the cable strands for bundling and arrangement as the individual wires are placed.

Work in September included the installation of the turning tracks for the travelers at the western deviation saddles. These tracks are to allow continuous motion of the traveler across the western end of the main span. By mid-October, the traveler cables were installed. A temporary group of tower stay cables to the west, intended to resist the overturning forces imposed by the bare main cable, have also been installed. Subsequently, the eastern deviation saddles were installed, preparing the bridge for cable placement.

Cable placement[Bearbeiten]

The cable construction technique differs significantly from that used for the earlier western spans and similar conventional suspension bridges. In that method, the cables were spun only a few wires at a time, with bundles made up as the wires were spun by pulling a loop along the cable's route. The SAS uses a different technique, with the wire strands pre-fabricated into mile-long cable bundles with bundle terminations already in place, pulled by dragging one end through the route. After attachment to the termination a tensioning operation is performed on each bundle at the eastern anchor point, and the bundles are suspended a few feet above the catwalk. A total of 137 such bundles have been emplaced. As bundles were positioned, they were temporarily tied together to form the cable. The cable was completely in place in late May 2012, followed by compaction to a circular shape, now being wrapped with a protective wire jacket. In mid-March 2013 the western portion was completed and the catwalks have been removed. Wire wrapping continues on the eastern portion.

Suspender saddles and suspender cables[Bearbeiten]

Since the main cables curve and the suspender cables splay outward to the deck edge, saddle design is individual to the location, being fabricated in mirror image pairs for each side. As of mid-June 2012, most saddles are in place upon the main cable. Wire rope suspender cables have been draped over these saddles and are being pulled outward and attached to projections from the main deck.

Suspender cable adjustment[Bearbeiten]

On a conventional suspension bridge, sections of deck are hung in place and so immediately tension the suspenders. The proper initial length of each suspender predetermined by engineering calculations and adjustments are required for segment relative positioning and equality of load distribution amongst the several suspenders of the section. On this bridge, the deck sections are already in a fixed relative position (being joined together and resting upon the falsework) and all suspender cables must be brought to specific tensions individually in order to tension the main cable. The jacking saddle is used to balance the tension among the segments of the main cable.

Tensioning is performed in stages and has been likened tuning a giant harp. The degree of tensioning at various stages and the order of tensioning is critical to this procedure.[80]

Phase Description Status
1 SFOBBESR-TensioningPhase1.jpg Jack and tension 26 of 50 suspender groups each side (8 at a time in 3 steps) 2 in the fourth step and then final adjustments in steps 5 to 18. In the first 8 steps - 80% of the load will be transferred from the temporary truss to the cable. Begun late August 2012, completed
2 SFOBBESR-TensioningPhase2.jpg Jack and tension 3 more suspender groups out of 50 for each side to bring to a total of 29 of 50 each side. Begun early October 2012, completed
3 SFOBBESR-TensioningPhase3.jpg Jack and tension final 21 of 50 suspender groups to bring total suspenders tensioned to 50 out of 50 each side. Begun late October 2012, completed

Bridge becomes self supporting[Bearbeiten]

Starting in 2011, proper balance between main cable runs and suspender cables and proper tension were applied to the main and suspender cables. On November 20, 2012, this process was completed which made the SAS portion of the bridge self-supporting.[4] Only now may the falsework be removed.

Yerba Buena Island Transition Structure[Bearbeiten]

Several construction phases can be seen in this early 2011 image, from finished columns to falsework erection through formwork completion prior to concrete pouring.
Left: Temporary double deck S-Curve (upper deck is westbound toward tunnel).
Center: Southern columns (for eastbound traffic from tunnel lower deck).
Right: Northern columns, falsework, and formwork (westbound to tunnel upper deck).

The Yerba Buena Island Transition Structure (YBITS) is an elevated roadway that will connect the gap from the SAS span to the Yerba Buena Island tunnel. Much like the Oakland Touchdown on the other side of the new bridge, this section of the bridge is also an end segment, meaning that the purpose of this segment is only to transition portions of the existing bridge to the main spans of the new bridge currently under construction. Since the SAS span consists of two parallel roadways, and the YBI tunnel has upper and lower deck roadways, this connecting structure must transition the SAS span's side-by-side roadways to the upper and lower decks of the YBI tunnel.[81] The YBITS is a significant structure to the new eastern span since it is referred to as "The link between the new and the old".[82] As of mid-February 2012, the northern structure has been poured and formwork was being removed. As of early September 2012, the falsework has been removed, modified, and constructed at the eastbound location with formwork completion now allowing reinforcing and concrete placement.

Column design[Bearbeiten]

There are a number of columns supporting this structure. As the ground level rises from the shore to the level of the Yerba Buena Tunnel, the height of the above ground portion of the columns will vary. Since the rock structure supporting these is a hard shale, it would be normal under previous engineering methods to simply dig a relatively shallow foundation for each column, with the structural length varying progressively. Modern seismic analysis and computer simulations revealed the problem with such a design; while the long columns could flex several feet at the top (0.6 meter, more or less), the shorter columns were likely to break, since the rigid deck structures cause the imposition of a similar amount of motion at the tops of the columns, imposing more bending stress per unit length on the shorter columns. This sensitivity was solved by making the columns of similar (but not uniform) length, with the "shorter" columns extending in permanent open shafts to deep foundations. This allows all columns of the YBITS to respond in a sufficiently uniform manner. The space between a column and its pit is covered by a protective sacrificial cover, forming a type of base isolation system at the more sensitive column locations.[83] In addition, the western landing of the YBITS is a zero moment hinge, and so there are no bending stresses at that point.

Construction techniques[Bearbeiten]

In order to build this complex structure, the construction process consists of several steps that are shown below:

The first step is to construct foundations of the large columns that will support the elevated roadway of the YBITS. Above-grade column reinforcing is constructed and enclosed by formwork and concrete is emplaced. After curing, the formwork is then removed. The next step is to build the actual roadway itself. The two principle techniques that may be employed are the use of precast, post-tensioned segments (as were used to construct the eastern "skyway" approach), or to cast the spans in place, using extensive reinforcing, (the method used for the YBITS) often with post-tensioned cable tendons. In this case, the roadways consist of hollow box structures, cast in place in sections using formwork, owing both to the complex shapes involved and the necessity of maintaining traffic flow on adjacent structures during construction.[84]

Viewed from a completed portion of YBITS, this double-deck tunnel connects the eastern and western spans.

The following sequence is applied to each span between columns:

  1. Since the wooden or metal form that will support the casting of the concrete will be elevated, the forms must be supported on falsework, in this case using vertical pipe sections, steel beams, and diagonal cables. A wooden deck is then erected atop the falsework to support the lowest forming surface.
  2. Reinforcing for the lowest surface of the box structure is then added and the concrete is poured.
  3. Upon the initial pour, reinforcing and formwork for interior shear beams and any included tendon conduits are added and another concrete pour is performed.
  4. Then, interior formwork to support the upper (deck) surface is added and the rebar-pour process is repeated.
  5. After the concrete is sufficiently cured and any tendons are tensioned, the formwork and falsework may be removed, leaving only the concrete surfaces to be seen.

Island ramps to link to YBITS[Bearbeiten]

Yerba Buena Island ramps
  • Caltrans eastbound on-ramp (to be constructed)
  • City of San Francisco Yerba Buena Island westbound on-off ramps (proposed)

Other than the current westbound off ramp (to be replaced), existing ramps linking the bridge traffic to Yerba Buena Island and Treasure Island are inadequate to handle traffic for future expected residential development. In particular, the eastbound off ramp has always been extremely hazardous, while added westbound on ramp traffic would interfere with bridge traffic flow. Between the tunnel's western portal and the existing western suspension span there is simply no room for modern ramp configurations. The developments are expected to add some three thousand residents to the island plus business and office space. To support this traffic, new ramps will be built on the eastern side of the islands to link to YBITS, where there will be adequate room for proper traffic merges and departures.

Lighting[Bearbeiten]

The Skyway and YBITS structures will have custom lighting using 48,000 high-performance LED's grouped in 1,521 fixtures, most of which are mounted on 273 poles.[85] These fixtures were designed by Moffat & Nichol and built by Valmont Industries. Within a specific fixture the beam pattern of each LED is restricted by a masking structure. Each fixture will be adjusted independently and with the LED masking will illuminate the roadways only in the direction of travel, similar to the vehicles' headlights and so greatly reducing glare presented to drivers by earlier fixtures. This is expected to improve safety for travelers. The main span roadway will be illuminated by downward-pointing LED fixtures mounted upon the main cable suspender saddles.

These lights use about half of the power of the old bridge's lights and will last about 5-7 times longer. They will only have to be replaced every 10–15 years (compared to every 2 years with the old east span), reducing cost, improving worker safety and reducing traveler inconvenience due to lane closures.

SAS construction simulation and site cameras[Bearbeiten]

A movie simulation is available at this Metropolitan Transportation Commission (MTC) webpage: MTC – News. This shows the placement of the bridge deck sections and the use of a jack-up crane to erect the tower scaffold, with the placing of sections of the tower by a gantry atop the scaffold. This simulation takes the construction up to its current state as of late May, 2011 and does not include the cable spinning. For current site camera views, see this MTC site. These cameras include views of the SAS and YBITS, both panoramic and with specific views.

Videos[Bearbeiten]

Documentary[Bearbeiten]

This ten-minute documentary includes the earthquake damage, design, and some of the construction processes.

Fly-through computer simulation[Bearbeiten]

Construction simulation[Bearbeiten]

Earthquake response features and simulation[Bearbeiten]

This video explains some of the seismic response features.

Time lapse of S-curve insertion[Bearbeiten]

New span construction[Bearbeiten]

This starts with workers emplacing a section of formwark for a column, installing the first tower segments, international suppliers noted, etc.

Original span construction documentary[Bearbeiten]

This United States Steel documentary on the building of the original SFOBB shows the conventional (individual wire) cable spinning method starting at 7 minutes in with the anchorage eybars and continuing with building the catwalk, spinning the cables, and placing the suspenders. As with the replacement span, American Bridge was a major contractor on that job, too.

Entire project drive-by and fly-by videos[Bearbeiten]

A video from early June 2011, taken from a westbound coach in the right lane, gives a good overview of the project at about the same speed as it will be driven upon by its users during non-rush hours. There is no narration, but in an earlier version we could overhear the remarks of the riders — e.g. "Look at this big monstrous thing here!" [the tower scaffold] and "Oh, guys, I hope it's worth it!".

0:00 – The Westbound touchdown (white "object" to left is a reflection of the sky through the windshield)
0:11 – The east end of the westbound skyway
0:13 – The first of three dual foundations that will support the eastbound touchdown
0:17 – The eastern end of the eastbound skyway
0:26 – A crossing between the eastbound and westbound skyway for the workers and inspectors
0:55 – Three poles, first of many to hold lighting fixtures
1:00 – Barges anchored in the distance are used to carry major bridge components
1:04 – A typical observation point for the pedestrian and bicycle path
1:15 – The roadbed on the last causeway segment curves to join the truss portion of the old span
1:21 – The first of the five through-truss spans is entered
1:30 – The spans of the skyway segments become shorter where the skyway curves
1:51 – The first steel box structures are seen, supported by temporary towers
2:09 – Entering the cantilever span
2:12 – The eastern main-span support is surrounded by falsework that will support the final SAS deck segments
2:22 – The SAS tower and its erection scaffold appears as the coach slows for the S curve
2:42 – Cross boxes can be seen here joining the east and west box deck structures
2:47 – The little red vehicle has nowhere to go except on the SAS
2:50 – Main span western counterweight
2:52 – Yellow tubular sacrificial keys will align the SAS to the YBITS
2:54 – Leaving the cantilever span to the S curve
2:56 – YBITS formwork for the westbound lanes
3:00 – Column head rebar
3:06 – Personnel access stairs
3:13 – Column casting formwork — from here, we see a mix of tall and short columns where the roadbeds will transition from side-to-side to over-and-under configuration
3:19 – Completed portion of the YBITS
3:24 – End of video, coach is about to enter the Yerba Buena Tunnel

A fly-by video was also shot on the same day from above. This video shows the current traffic and the construction progress of the SAS from an extraordinary aerial view.

Einzelnachweise[Bearbeiten]

  1. Michael Cabanatuan: Bay Bridge to open on Labor Day 2013. In: The San Francisco Chronicle, February 8, 2012. 
  2. FAQs. In: San Francisco–Oakland Bay Bridge Project. California Department of Transportation. Archiviert vom Original am July 24, 2007.
  3. http://baybridgeinfo.org/sas-travelers-page
  4. a b http://www.sfgate.com/bayarea/article/Bay-Bridge-span-s-Big-Lift-complete-4055497.php#src=fb
  5. (Skip to 2:00 to end of video)
  6. The Bay Bridge: Competing Against Time. In: 60 Minutes, CBS. 
  7. Oakland Bay Bridge Zusammenbruch
  8. Major quake on Hayward fault more likely, scientists say. In: Contra Costa Times. 
  9. Vorlage:Cite report
  10. Unparalleled bridge, unprecedented cost. In: SF Public Press. 
  11. Span Design Displeases East Bay.... In: San Francisco Chronicle, June 11, 1998. 
  12. An Innovative Curved Cable-Stayed Bridge U. C. Berkeley, Civil Engineering Department
  13. A Bridge Suspended in Controversy Wired magazine website
  14. Abolhassan Astaneh: Letter to Will Kempton (PDF) University of California, Berkeley. February 18, 2005. Archiviert vom Original am August 30, 2005.
  15. Controversy Swirls Around Proposed Bay Bridge Re-Design California Planning &Development Report
  16. Timeline of the San-Francisco-Oakland Bay Bridge Seismic Retrofit
  17. Vorlage:Cite report
  18. SF Bay Bridge may have been lost jobs opportunity, NBC News. 
  19. San Francisco Bay's new span a made-in-China affair. In: The Press Democrat. 
  20. World Steel Association World Crude Steel Production
  21. Hard Decisions Before the Legislature: Toll Bridge Seismic Retrofit California Legislative Analyst's Office
  22. Toll Bridge Seismic Retrofit Funding History and Options California Legislative Analyst's Office
  23. Funding Agreement Allows East Span Construction to Move Forward Transactions Newsletter Online (Metropolitan Transportation Commission)
  24. KTVU-TV website posting 4354824
  25. KTVU-TV website posting 4404183
  26. U. S. Department of Transportation Office of Public Affairs, Oct 21, 2005
  27. Index to summaries and full reports by the consultants
  28. Vorlage:Cite report
  29. Executive summary (Teal)
  30. Fischer summary – MS Word document accessed via this Federal Highway Administration page
  31. Bridge welds pass U.S. muster. In: The Sacramento Bee. 
  32. Vorlage:Cite press release
  33. Bay Bridge reopens (SFGate.com – San Francisco Chronicle)
  34. John Upton: Car chaos forecast for bridge re-repair. In: San Francisco Examiner, November 30, 2009. 
  35. John Upton: Take two: Bay Bridge repair withstanding strong wind gusts. In: San Francisco Examiner, December 8, 2009. 
  36. Questions raised on Bay Bridge structural tests. In: The Sacramento Bee. 
  37. http://www.sacbee.com/2012/05/26/4519092/Caltrans-records-reveal-concerns.html
  38. http://www.sacbee.com/2012/05/30/4524460/Caltrans-open-to-outside-experts.html
  39. Press release with copy of later to Sacramento Bee June 2, 2012 (Caltrans)
  40. Joyce Terhaar: From the Editor. In: Sacramento Bee. 
  41. http://www.sacbee.com/2012/08/04/4693812/Caltrans-records-show-problems.html
  42. http://www.sacbee.com/2012/08/15/4726601/lawmakers-want-outside-review.html
  43. Bolts Snap on Bay Bridge's New East Span, Repairs Could Cost Up to $5 Million KQED News Blog
  44. Engineers Zero in on Bay Bridge Broken Bolt Solutions KQED News Blog
  45. Emperor Norton's name may yet span the bay. In: San Francisco Chronicle. 
  46. Oakland takes dim view of bid to rename Bay Bridge. In: San Francisco Chronicle, December 16, 2004. Archiviert vom Original am July 26, 2007. Abgerufen am September 2, 2007. 
  47. Vorlage:Cite press release
  48. Engineering Geology of San Francisco Bay, California The Geological Society of Americal(R) An informative article concerning the various layers of underwater soil (including the Alameda formation) down to the bedrock Franciscan formation
  49. Image Caltrans District 4 photo site showing cast in place segment atop a column
  50. Oakland Touchdown Detours - Bay Bridge Info
  51. Oakland Touchdown Information - Bay Bridge Info
  52. Bay Bridge Construction Scheduled for Memorial Day Weekend, KRON-TV. 
  53. re: New eastbound touchdown: author driving experience, lack of newsworthy problems
  54. Bay Bridge Reopens Early! Metropolitan Transportation Commission
  55. A video of the new eastbound detour is shown here.
  56. Bay Bridge Info Construction Cams
  57. Getting the word out on Bay Bridge closure over Labor Day weekend, San Francisco Chronicle August 26, 2007
  58. San Francisco-Oakland Bay Bridge Seismic Safety Projects E-Newsletter Vol. 3, Accessed December 22, 2007
  59. Construction Webcam
  60. Michelle Quinn: The S-Curve: Must Engineers Assume Drivers Will Behave Badly?. In: The New York Times, November 10, 2009. Abgerufen am May 1, 2010. 
  61. Changes coming to Bay Bridge after death plunge. In: San Francisco Chronicle, November 10, 2009. 
  62. Unlike black-on-white or white-on-black rectangular speed limits, advisory signs are black-on-yellow in a diamond shape. 35 mph speed advisory and additional rumble strips observed March 2011.
  63. Bay Bridge Slaughter Curve Update CBS 5 - Nov 9, 2009 11_30 PST CBS5 news article after fatal accident demonstrating difficulty of seeing speed limit signs and Caltrans proposed modifications (on YouTube)
  64. Work Moves Forward On Bay Bridge Eastern Span, KPIX-TV. 
  65. SAS Construction | Bay Bridge Info
  66. Vorlagenfehler: Parameter title wird benötigt. 
  67. BATA MTC 4Q 2010 report
  68. http://www.mtc.ca.gov/news/current_topics/10-11/sfobb.htm
  69. 2010 Third Quarter Project Progress Report... California DOT (See page 53)
  70. One-of-a-Kind Design
  71. Tower sections arrive (Oakland Tribune)
  72. Contra Costa Times video (second video has animation)
  73. Mercury News article on tower erection
  74. Read all the press releases and the info on the right column
  75. This press release has all the information shown in this paragraph
  76. Final Phase Update April 15, 2011
  77. Phase Five Factsheet
  78. One-of-a-Kind Design Structure magazine webpage
  79. http://baybridgeinfo.org/projects/sas#.UC2Rb45HZcw (Description of suspender cable tensioning)
  80. Suspender cable tensioning text and images from the Caltrans 2012 second quarter report (Published late August 2012)
  81. YBITS Factsheet
  82. Quote from this website
  83. CBS News video 60 Minutes Video Extra
  84. Click on Yerba Buena Island Cameras FIXED to see the construction of the wooden cast
  85. http://baybridgeinfo.org/lighting
==External links==
{{commons category|Eastern span replacement of the San Francisco – Oakland Bay Bridge}}
*[http://www.baybridgeinfo.org/ Bay Bridge Project official website] Caltrans
*[http://www.dot.ca.gov/baybridge/seismic_retrofit_program_reports/ Index of quarterly reports of the Bay Bridge project] Caltrans
*[http://www.dot.ca.gov/dist4/eastspans/index.html San Francisco-Oakland Bay Bridge East Span Seismic Safety Project] Caltrans
*[http://www.uctc.net/research/diss130.pdf The Making and Un-Making of the San Francisco-Oakland Bay Bridge: A Case in Megaproject Planning and Decisionmaking] Dissertation by Karen Trapenberg Frick, Doctor of Philosophy in City and Regional Planning
*[http://www.library.ca.gov/crb/04/13/04-013.pdf Timeline of the San-Francisco-Oakland Bay Bridge Seismic Retrofit] 1929–2004 Prepared for the Joint Legislative Audit Committee
*[http://www.mtc.ca.gov/planning/bay_bridge/bbhist.htm East Span Replacement Timeline] 1997–2013 Metropoliton Transportation Commission
*[http://sfpublicpress.org/news/2009-12/unparalleled-bridge-unprecedented-cost Unparalleled bridge, unprecedented cost] SF Public Press
*[http://www.sfweekly.com/2004-03-17/news/a-bridge-too-weak "A Bridge Too Weak?"(Engineering concerns about the self-anchored main span design)] SF Weekly
*[http://www.Caltrans.ca.gov/baybridge/MainSpanReportDraftDec10.1230.pdf Caltrans Alternatives report December 10, 2004] Caltrans
*[http://sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/12/15/MNGUMAC6LN1.DTL "Emperor Norton's name may yet span the bay" San Francisco Gate story on renaming the bridge] SFGate (San Francisco Chronicle website)
*[http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2006/03/21/MNGD8HRJ761.DTL "TOWERING QUESTION – WILL IT FINALLY BE BUILT?" – SFGate summary about the construction delays]
*[http://www.thebridgesofar.com/ "The Bridge So Far – A Suspense Story"] A 2006 documentary film chronicling the delays in construction
*[http://articles.sfgate.com/2009-01-26/bay-area/17196916_1_welds-eastern-span-bay-bridge "Cracks In New Bridge Deck Panels"]
*[http://articles.sfgate.com/2009-08-26/bay-area/17176241_1_span-deck-contractor "2nd Article Cracks In New Bridge Deck Panels"]
*[http://articles.sfgate.com/2010-01-22/bay-area/17834810_1_bay-bridge-western-span-bridge-deck "Bridge Deck Panels Finally Arrive"]

{{DEFAULTSORT:Eastern Span Replacement Of The San Francisco-Oakland Bay Bridge}}
[[Category:Bridges in the San Francisco Bay Area]]
[[Category:Bridges under construction]]
[[Category:Self-anchored suspension bridges]]
[[Category:Transportation in Alameda County, California]]
[[Category:Proposed bridges in the United States]]
[[Category:Suspension bridges in the United States]]
[[Category:Road bridges in California]]
[[Category:Pedestrian bridges in California]]
[[Category:Interstate 80]]
[[Category:Bridges on the Interstate Highway System]]