eastward replacement of the San Francisco-Oakland Bay Bridge is a construction project to replace an unhealthy Bay Bridge section with a new self-anchored bridge (SAS) and a pair of viaducts. The bridge is located in the US state of California and crosses the San Francisco Bay between Yerba Buena Island and Oakland. Built between 2002 and 2013 and has no name other than the unofficial name of the bridge as a whole ("San Francisco-Oakland Bay Bridge"). The eastern landscape replacement is the most expensive public works project in California history, with a final price of $ 6.5 billion, a cost of 2,500% from an initial estimate of $ 250 million. Originally scheduled to open in 2007, some issues delayed opening until September 2, 2013. With a width of 258.33 feet (78.74 m), it consists of 10 general purpose lanes, currently the largest bridge in the world, according to Guinness World Recordings.
The Bay Bridge has two main parts: the western suspension range and their approach structure between San Francisco and Yerba Buena Island (YBI) and the structure between YBI and the eastern end of Oakland. The original eastern part consists of a balanced double cantilever range, five ranges via truss, and a truss causeway.
The original range of the eastern bridge of Yerba Buena Island became the subject of concern after the collapsed section during the Loma Prieta earthquake on October 17, 1989. The replacement range was engineered to withstand the largest earthquake estimated over a 1500 year period, and is expected to last at least 150 years with proper maintenance.
Video Eastern span replacement of the San Francisco-Oakland Bay Bridge
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It has been known for more than 30 years that a major earthquake in one of two nearby faults (San Andreas and Hayward) can destroy the main cantilever range. Little was done to overcome this problem until the 1989 Loma Prieta earthquake. The earthquake measured 6.9 on the magnitude scale and while the epicenter was far from the bridge, the foot section as high as 50 feet (15 m) from the upper deck of the eastern bridge the bridge at the bottom of the bridge collapsed onto the deck below, indirectly causing one death at the point of destruction. The bridge was closed for a month as construction workers moved and reconstructed the falling section. It reopened on November 18, 1989, with a stronger new retrofit in place. The failure occurred in the transition between the easternmost through the truss and the causeway segment of the two most western decks, the location where the inertial character of the structure makes a sudden change. The event analysis completed by internal staff has shown that the bridge was close to a much more catastrophic failure where either through-truss or cross-road segments will drop from their general support structure.
It is clear that the eastern landscape needs to be made more earthquake resistant. Estimates made in 1999 put the possibility of a major earthquake in the area in the next 30 years by 70%, although a recent study announced in September 2004 by the United States Geological Survey has raised doubts about the predictability of a major earthquake based on the duration before the quiet period. More recent analysis (2008) confirms the possibility of a major increase in events on the Hayward Fault.
Maps Eastern span replacement of the San Francisco-Oakland Bay Bridge
Designing a proposal
Retrofit
The initial proposal for the eastern landscape involves the construction of substantial concrete columns to replace or supplement existing support. There will also be modifications to the lattice beam as it is now complete for the western suspension range. The original cost estimate for this repair is $ 200 million. The overall appearance will be slightly changed. Due to the retention of the original structure, the ongoing maintenance costs of the bridge will continue to be high. The retrofit constancy is questioned directly by the Army Engineers Corps in a very important report and indirectly by the collapse of a bridge installed at the 1994 Northridge earthquake in Los Angeles, a structure that has been modified in response to San Fernando. earthquake 23 years earlier.
Substitution
Engineering and economic analysis in 1996 showed that replacement bridges would cost several hundred million more dollars than retrofits from existing eastern landscapes, would have a much longer life span (perhaps 75 to 100 years instead of 30), and would require much less maintenance. Rather than retrofit existing bridges, CalTrans (California Department of Transportation) decided to replace the entire eastern span. The proposed design is a high viaduct consisting of reinforced concrete columns and various precast concrete segments as seen in the illustration on the right. The design criterion is that the new bridge must withstand an 8.5 magnitude earthquake on one of several fault lines in the area (especially the San Andreas and Hayward fault). Aesthetic proposals are not well received by the public or their politicians, which are characterized as "expressways".
After this, the design contest is held for the signature range (range 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 are checked until all but four proposals submitted by EDAP members are selected as semi-finalists, and winners are selected from this group. This raises serious conflicts of interest, as EDAP members who choose bridge designs review proposals by their own companies and reject all proposals that have no representation in EDAP. The design chosen is more expensive than the alternative, because the main structure can not stand alone until it is structurally completed. This requires the construction of two bridges, the first falsework to support the final range, which will be removed after the completion of the final range. It has also been criticized as a less structurally robust design and with construction costs that are less predictable than other modern ranges.
Alignment
In 1997, there were many political disputes over whether the bridge should be built north or south of the existing bridge, with "Mayors Brown" (Willie Brown and Oakland's Jerry Brown from San Francisco) on the opposite side of the matter. Yerba Buena Island is within the bounds of San Francisco and the proposed northern alignment (and now) will overshadow a major development site on the island's east coast. Even the US Navy (at that time the island's controlling authority) was involved on the orders of San Francisco in restricting the access of Caltrans soil engineers to the proposed location. That might cause a two-year delay and hundreds of millions of dollars in additional fees.
Options are specified to be considered and carefully examined jointly by state and federal authorities, with input from the Coast Guard of the United States.
Class alternatives include:
- Extend the approach of sea level to the west, with a steep approach to the range.
- Use relatively constant values, including some ranges.
- Uses a relatively constant value near the range, with a range level.
The last alternative is chosen because it is considered to have superior visual effects and better driving experience. The value of a new approach to the channel range is somewhat less than the previous structure and less ship permits are provided under the range mainly due to the depth of the deck box structure.
Alignment alternatives include (see the image on the right for details):
- Q4: south straightening, slightly curved, but a shorter route than the north alternative.
- N2: two-tick north alignment is close to the existing bridge.
- N6: single loop alignment, with the main range leading north to the curve eastward viaduct, which is in line with the existing double deck truss-truss approach.
The last alternative is chosen, as it presents San Francisco's superior view to the west compared to others where the views are obscured by Yerba Buena Island. Other north lines will face more difficult geotechnical situations.
Naming proposal
In December 2004, the San Francisco Supervisory Board, in honor of Joshua A. Norton, issued a resolution "urging the California Department of Transportation and California and Senate Assembly members to name the new addition to the San Francisco Bay Bridge in honor of Emperor Norton I, Emperor of the United States and Protector Mexico. "The proposal is not supported by the Oakland City Council and the bridge has no official name.
Offering and initial construction
Although somewhat controversial, authorities decided to allow bids to include key components and materials that were not made in the United States. This is partly due to material costs, and primarily due to the lack of appropriate fabrication facilities in the United States, or even in the western hemisphere. In contrast, China, where the components of the SAS deck are built, has a low cost material producer. The other major components are produced in Japan, due to the availability of large steel casting capability, welding, and machining. Sadel suspension made in UK. Since the Federal toll fund generally comes with "US-made" restrictions, the bridge is built without such funds, which would otherwise be eligible for transport on Interstate 80.
Authorities were surprised when they opened bids on the proposed section of the tower and only one bid for the $ 1.4 billion it received, far more than their forecast of around $ 780 million. This is partly due to rising costs of steel and concrete, mainly as a result of the concurrent construction boom in China, but also due to construction uncertainty due to its innovative design. The entire project, which requires 100,000 tonnes of structural steel, is estimated to cost $ 6.2 billion as of July 2005, up from a 1997 estimate of $ 1.1 billion (for a simple bridge) and a March 2003 estimate of $ 2.6 billion covering a range tower. Despite increased costs, construction began on a replacement on January 29, 2002, with a settlement scheduled for 2007. The range finally opens on September 2, 2013.
Removal of the signature range
On September 30, 2004, the office of Governor Arnold Schwarzenegger announced that, without sufficient funds passed by the legislature, bids must be allowed to expire. It was, at the time, unclear whether this would require redesign to get a cheaper range.
- Six alternative proposals in 2004
On December 10, 2004, the governor's office announced that the concept of the signature range had been canceled, with the bridge to be the simple bridge originally proposed. The design, once full circle, remains expensive due to the high cost of materials. Many argue that there will be slight differences in final costs with this lower proposal because the concept requires a new permit, perhaps adding another two or three years; furthermore, viaduct can not even obtain Coast Guard approval, since the maximum width of the ship's channel will be reduced by almost half. The local reaction to this announcement is intense, with most suggesting that the bridge was built to emerge as proposed - either in steel material as an offer or using reinforced concrete towers that have similar appearances but at a lower cost.
Restore original design
The viewpoint of pro-"signature bridge" activists and local politicians was reinforced by legislative analyst reports at the end of January 2005. The report indicated, due to additional time delays and all new licensing requirements, that the vizon proposal from the governor would likely require additional funds and take time longer to complete than the proposed range of signatures. This view was reinforced by a further report in March 2005 which indicated that delays imposed by the governor had added at least $ 100 million to the expected cost (later changed to $ 83 million in a December 2005 report).
The design controversy continued for more than six months. In essence, the governor believes that all countries should not share the cost of building bridges, because he considers them a local problem. Northern California shows that when the southern part of the country is disastrous, the state supports rebuilding, particularly seen in the rebuilding of the earthquake highway and subsequent retrofitting of the state highway structures and bridges. Since the goal of replacing the eastern span is to prevent rebuilding needs after a major earthquake, Bay Area residents feel justified in their call for state support.
A compromise was announced on 24 June 2005 by Governor Schwarzenegger. The governor said that he and the President of the State Senate Pro Tempore Don Perata have reached an agreement to revive plans for the signature range. The cost estimate of the cost of contract delays and the inflation range caused by the delay ranges up to $ 400 million. Direct costs due to termination of work include some demolition of temporary structures and their reconstruction after the next restart.
Once approved by the legislature, the compromise law written by Senator Loni Hancock was signed by the governor on July 18, 2005. The compromise called on the state to donate $ 630 million to help cover $ 3.6 billion in cost swelling, and the cost of the bridge to be raised to $ 4 starting in 2007. At the time of signing, the bridge section of the bridge is 75 percent complete and the state is beginning to prepare to delay suspension for new offers. The entire project is then scheduled to be completed in 2013 with an estimated cost of $ 6.3 billion, excluding the dismantling of the old range.
In January 2006, the cost for the main steel structure work was determined to be $ 400 million more than this expectation. The new offer for the main range was opened on March 22, 2006, with two shipments at 1.43 and 1.6 billion USD. Since the reserve was built with $ 3.00 tolls during the delay, it was initially advised by the authorities that an additional fee exceeding $ 4.00 would not be required, but because of the additional costs in other parts due to delays and re-start the foundation cost of the main working range, $ 5.00 is now expected. (Toll only collected in the west.) Low offer by American Bridge and Fluor Corp joint venture, named 'American Bridge-Fluor , was accepted on April 19, 2006.
Design and construction
Skyway Viaduct
Skyway viaduct connects the SAS section of the bridge to the Oakland beach. In 2007, 75 percent of the skyway section was completed. Because this section cuts off the shallower part of the bay, its foundation is built inside a crate of piles. In mid-2009, the last connection of the viaduct section to the ground surface at the eastern end was being completed and the pedestrian walkway was attached to the completed section.
Instead of arranging a heap deep enough to reach the bedrock, the pole was erected in the company's silt mud under soft mud deposited by miners deep in the late 19th century. Since even the primitive mud is too weak in the application of this concentrated load for conventional vertical friction stacks, large diameter tubular pylons are moved (inside dried-pumped cofferdip) at an angle, forming a "thrown" (outstretched) foothold, through ancient mud. into the aggregate company of sand, mud, and gravel formation Alameda. Where long pole is required, segments are welded together as segments are completed.
When all the poles are in place, the reinforced concrete pads are poured at the bottom of cofferdam to form a foothold for the columns, then cast around the rebar using a reusable metal formwork.
A single viaduct segment located above each column is placed using a form. The sponge pair of precast spans, made in Stockton, California, are pushed to the location and lifted into place with a special cantilever lift. (Cantilever elevators, counterweight and other equipment and materials are lifted either by a barge crane or by a jack-up crane located between adjacent columns.) Once in the right location, opposite segments can then be combined with through tendons (wires inside channel tightened by jack), forming a balanced cantilever above the column. Finally, the distance between the columns is closed, forming a tendon bony beam.
Oakland Touchdown is a curved overpass that connects the sky to the Oakland coast (the beginning of the bridge). The curve is needed to bring harmony to the existing land-level approach. Like the Yerba Buena Island Transitional Structure (YBITS) in the west of the main range, this section is also the final segment of the new bridge and is being built at the same speed as YBITS. The construction process consists of two phases, the first stage is completed (west side of the traffic). The eastward touch can not be completed until the existing path is not working. This is done by building a soft swing to the south so that touchdown can be completed. The first phase of this work is to move the east-to-south traffic settled with only minor traffic delays during the Memorial Day 2011 holiday (28-30 May). The driving experience has been improved, without the problems that come with the famous S-curve . The second stage of moving traffic westward to the space available requires the construction of an elevated approach. This was completed on February 19, 2012. The recently designed procedure is expected to save time in total effort, speeding up the completion of the range. Oakland Touchdown completed in March 2013.
On the three-day weekend starting at 8:00 pm Friday, 17 February 2012, the westbound lanes are closed to allow highway connections to approach with new temporary structures. The execution of this task depends on the weather, dry conditions required for re-striping of lines, and it is not specified until a few days before that work will be done this weekend. Originally scheduled to finish at 5 am. on Tuesday, February 21, the work finished 34 hours ahead of schedule, and opened for traffic around 7:15 pm. on Sunday, February 19th.
Primary range
The main range is a rarely built type, a suspension bridge. It's unique in being a single and asymmetric tower, a design tailored to the site. For boat duct cleaning, the bridge will require at least one long range, while ready access to the bedrock is found only close to Yerba Buena Island. The cable-stayed design of the two towers will require a very deep tower foundation, and a conventional two-tower suspension bridge will also require a large anchor to be built in the mud of the bay. The curved nature of this approach places additional constraints on the design.
While previous bridges of this type use chain eyebars, the long range required here uses wire cables, like other modern suspension bridges. Uniquely, this is a circle of cables rather than a pair of ordinary cables, and, instead of spun on the catwalk, large bundles of strands are dragged into place with temporary support on the catwalk, eventually suspended by tightening the strand. This strand bundle is then arranged to be finally compacted to form a complete main cable.
Being asymmetric, the shorter western range should be pulled down against the forces imposed by the eastern ranges again. To avoid removal of supporting columns, the range ends with the massive weight of the massive concrete. The end weight also carries a saddle for the main cable. As can be seen in the northwest corner image above, there is an upward component of the voltage force provided by the main cable, and it is this component which removes most of the end cap weight from the column. (The larger, horizontal, component is offset by the compressive force given by the box deck structure as a characteristic of this type of bridge.)
Segments of each of the two deck ranges will be retained in compression during a severe earthquake by an overlapping internal tendon joining the extreme end cap, performed internally in the cable tray. These tendons are needed because the support of the eastern ends is both much lighter than western counters and radically different soil conditions at each end, the western end is set in the bedrock while the eastern tip, with vertical support pushed onto the bedrock, is largely contained in mud soft, which responds more actively to seismic shocks than shale. The point is that the combination of the toned tendon and the squared road box structure will keep both end caps in the same relative position.
The bridge segment at each end is not a simple repetition of the central range segment. The extreme deck segment at the eastern end is curved and tilted to the fair to the curved part of the skyway. This extreme segment is also outside of the main cable cord anchor and the eastern support column and most of the bridges that join the skyway already exist (the gray section seen above). The extreme bounded eastward deck segment at the west end should be fair with the eastern horizontal portion of the YBITS connector, while the western (north side) segment starts up into the western YBITS, increasing traffic to the upper deck of the Yerba Buena tunnel.
S-curve construction
The old cantilevered bridge is connected to Yerba Buena tunnel with a deck truss causeway that includes curved sections. Since this structure occupies an area that must be clear for the new bridge approach, it is necessary to construct a completely new whilst approach to the old bridge. It's necessary to swing south to clear the area for new construction, and then back north with a heavier curve to connect to the cantilever. Since it will only be available a few days where the bridge can be closed for traffic, the curved part is built adjacent to its last position on the bridge extending below and beyond the old curved connector. During replacement, the old part is slammed out of the way (to the north), and the new part is installed in place.
- Image S-curve
On September 3, 2007, the first section relating to the construction of the new East Span, a temporary range of 300 feet (91 m) that connects the main cantilever portion to the Yerba Buena Island Tunnel, is incorporated into the service. Construction of new connector ranges beginning in early 2007 in addition to the existing range. Caltrans closes Bay Bridge over Labor Day weekend so the crew can replace the old range. After the old parts are removed, new spans are rolled out using computer-guided system jacks and hydraulic rollers. The new section has been secured and the bridge reopened 11 hours ahead of schedule, for the morning journey on September 4, 2007. In September 2009, during the close of a single holiday, a new temporary steel job to route traffic around the location of the last approach to the new bridge was enforced, and its connections to the exit of existing tunnels and bridges were completed, as was done in September 2007. This shortcut enabled the construction of a permanent transition structure between double deck tunnels. and a new side-by-side bridge structure. After completing the bridge, other additional closures allow for temporary structural relocation and completion of the road segment.
All parts of the old landscape over Yerba Buena Island (where the S-curve route traffic) is dismantled, and support for new ranges is currently being built at that location.
The S-curve site has become famous by accident, from fender-benders to fatal declines. Accidents usually occur during non-commuter time, when traffic flows faster, at or above the 50 mph common bridge boundary. Additional signs and visual and physical indicators showing the 40-mph S-curve speed limit installed after a major crash. The upper deck speed advisor on the curve was posted as 35 mph and an improved system of "rumbling strips" was installed.
SAS falsework
The entire deck structure should be supported in the proper alignment up to:
- Close end with anchor and twist and strain the saddle is complete.
- The tower with the main saddle is over.
- All deck segments are already installed and joined.
- The internal tendon is placed and tightened.
- The main cable is playing.
- All suspender cables are fitted and adjusted to the tension.
- The main cable tension is balanced on each side. (This is maintained when the suspender cable is tightened.)
Falsework to perform this task is a pair of substantial truss bridges, prefabricated in segments, with columns and spans segments lifted into place by barge tugs. The beams are supported on a foundation consisting of or built on a deeply driven pole. Upon completion of the bridge, all falsework structures and all exposed underwater support will be moved to create a secure channel for deep deep vessels transiting to and from the Port of Oakland.
Deck placement
At the end of August 2009, temporary column work was completed, the truss range was in place and the prefabricated section was being placed on it. A giant barge crane, Left Coast Lifter , is used to place 28 main deck box structures. The main segment placement in the SAS section of the bridge was completed in early October 2011. On October 19, 2011, a small gap between the SAS deck and the curved skyway extension was eventually closed to the east-bound side, and the west-bound gap was closed the following week. As of November 2011, the placement of the SAS range deck is completed, making it 1 ½ mile continuous path.
In July 2013, the entire SAS range is completed and the asphalt paved the way started. Each deck segment is paved with two single layers of asphalt and concrete that must be very durable and last for the entire lifetime of the bridge. However, the rest of the bridge is not paved with asphalt but only receive a protective coating.
Main landscape tower
This design uses extensive energy absorbing techniques to allow immediate survivability and access to emergency vehicles after the Maximum Current Earthquake (MCE), estimated at 8.5 large times over a 1500 year span. Instead of designing for stiffness, it is not a flexible structure, with resonance motions being absorbed by plastic shear sacrificial components, replaced. Smaller earthquakes would impose most of the elastic pressure on components, with a higher proportion of plastic (and thus energy absorber) emphasized in larger earthquakes. This design philosophy extends to other metal components of the bridge, including the victim's tubular end buttons that align the self-contained suspension with its approach structure at each end.
The tower consists of four columns. Each pentagonal column is approximately composed of four tapered and/or straight sections, coupled from end to end by the external plate and the radius of the inner finger joint secured by the fastener. The columns are also merged horizontally by the victim's box structure. This combined box is intended to absorb motion driven by an earthquake with elastic and plastic bending deformation while the tower shakes. Under a severe earthquake, this deformation absorbs the energy that can otherwise cause destructive tower movement, thus protecting the main structure of the span. It is hoped that this design will allow the immediate use of bridges for emergency vehicles, by joining replaced as needed to restore the bridge to its original state. Uniquely, this tower has no direct connection to the road, with enough space to allow it to sway under a severe earthquake without a collision.
Tower construction
The process to build the SAS tower on its foundation consists of five phases. The first four phases consist of lifting segments from four similar columns and straightening them to their place and to the elements that connect them, while the last phase is lifting the final top cover which will carry the crown of the main cord saddle. On July 28, 2010, the first of the four pillars of the main tower below was set up, had arrived at the beginning of the month by a barge from China. They are placed by lifting one end of the barge to the temporary scaffold, with the train in the barge to allow the lower end to move to its place. Once the pole is welded into its place, the scaffolds are then extended upwards to allow the next set of columns above the deck to be erected, lifted, and translated to position, a process repeated for each remaining phase.
The erection tower continued when the second column set finally arrived in the week of October 24, 2010, almost three months after the first set was placed. The second set of columns was established by a gantry on the scaffold and placed on the first four columns placed at the beginning of the year. Once the poles are installed, they are bolted together with the first column. After this second phase is completed, the tower is now about 51 percent complete and stands at a height of 272 feet. The third set of tower columns does not arrive until the week of December 15, 2010. The third set, now with a larger crane, is lifted and placed above the second column column. The tower now stands at an impressive 374 foot altitude and 71 percent complete. The erection process did not continue until the following year when the last set of tower posts finally arrived on Valentine's Day 2011. These four columns, each 105.6 feet high, were lifted on the week of February 28, 2011 and placed above the third set column. The tower now stands at an altitude of 480 feet and 91 percent complete.
The fifth and final tower phase is to lift the grillage (the structure to join the column, more commonly used as a foundation element) which weighs about 500 tons, lift the 450-ton main cable saddle, and finally lift the last head of the tower to complete the entire SAS tower. All these last pieces came to the site on the same day that the fourth tower pole arrived. On April 15, 2011, the first part of the fifth and final phase begins. 500 tonne grill lifted 500 feet in the air and placed above the fourth set of columns. The tower then stands at a height of 495 feet and 94 percent is completed. It took about a day to lift and place a grillage on top of the tower.
Booting double cable saddle saddle
Working all day 19 May 2011, operating engineers and iron workers raised and placed a double-sided 900,000 pound saddle above the SAS tower. While most of the span is made in China, this special section is made in Japan, such as saddle deviation east and west and the main hydraulic saddle jacking cable.
This cable saddle guides and supports the main cable along the miles above the tower placed at the end of the year. In December 2011, the placement of the SAS range deck has been completed and progress of cable construction has finally begun. However, several months earlier in July 2011, the head of the tower was lifted and placed over the saddle in test fittings and then removed to allow for the laying of cables. Then in 2012, the cables are fully placed in the saddle of the tower and then anchored across the entire SAS range. The tower head is then permanently installed for the last time, along with the plane warning beacon, completing the entire SAS tower at a final height of 525 feet (160 m).
SAS main suspension cable
Tower towers include eyebars for temporary cabling that support four sidewalks, each simple suspension bridge (called a catwalk) that allows access to the main cable and wire spinning mechanisms during construction. In some ways similar to a ski lift, additional superior cables carry one or more of these travelers, wheeled devices that move from one end of the span to the other, are pulled by arranging cables manipulated by multiple cranes.
- Picture cable
The main range uses a single cable, rotates using pre-mounted cable group from the anchor point at the eastern end of the main range, across the eastern corner of the saddle horizontal deviation, passes the vertical deviation buffer at the eastern end, upper and upper Half of the main tower saddle down into the arch 90 degrees on the west counterweight, across counterweight, through a hydraulic tensioning saddle, around the opposite west saddle deviation, up to the other half of the main saddle tower. , over the eastern vertical aberration of the saddle down the east end curve of the saddle end, to the corresponding anchor point in the anchor opposite east strand early.
When the bundle is laid, it is initially supported by a buffer mounted on the catwalk, then both ends are fitted and the cord is fastened to the east of the anchor. As with conventional cable suspension ranges, all tightened bundles are then compressed into circular shapes and protected by a circular wrapper of wire. Sadel for suspender cable is added and suspender cable is placed and tightened. Suspended cable tension lifts the range of its supporting falsework.
In mid-June 2011, preparations for major cable spinning started by installing a temporary catwalk on the SAS range. Both western catwalks are installed and by mid-August, all four of the catwalks are mounted in place and an approximate line of completed bridges can be seen. The four catwalks, traveler, suspension cable, drafting cable, and crane and special trajectory in the saddle deviation must exist before the strand raking can begin. This catwalk is required for workers access to the cable strands for bundling and arrangement when individual cables are placed.
The work in September 2011 included installing a turning track for travelers in the western deviation saddle. This track allows continuous movement of explorers across the west end of the main range. In mid-October 2011, the traveler's cable was installed. A group of temporary tower cables stay west, intended to counter the overturning force imposed by the bare main cable, is also installed. Next, the eastern deviation saddle is fitted, preparing the bridge for the placement of the cable.
Placement cable
The cable construction technique differs significantly from that used for previous western spans and similar conventional suspension bridges. In that method, the cables only rotate several cables at a time, with bundles being made as they rotate by pulling a loop along the cable route. SAS uses a different technique, with a pre-fabricated wire strand being a mile-long cable bundle with an existing bond termination, pulled by dragging one end through the route. After sticking to the termination, the tensioning operation is performed on each bundle at the east anchor point, and the bundle is suspended a few feet above the catwalk. A total of 137 such bundles were installed. As the bundles are positioned, they are temporarily bonded together to form wires. The cable was actually in place at the end of May 2012. It was then compacted into a circular shape, and then wrapped with a protective wire jacket. In mid-March 2013, the western part is completed and the catwalk is eliminated. Wire wrap is still going on in the east.
Since the main cable curve and suspender cable extend to the edge of the deck, the saddle design is individual to the location, fabricated in the mirror image pair for each side. In mid-June 2012, most saddles are mounted on the main cable. The suspender wire rope cable is then draped over this saddle and then pulled out and attached to the projection of the main deck.
On a conventional suspension bridge, some parts of the deck are hung in place and thus pull the suspenders immediately. The exact initial length of each suspender is determined by engineering calculations and adjustments are required for the position of the relative segments and the equivalent load distribution among some section suspenders. On this bridge, the deck section is in a relatively fixed position (put together and rested on falsework) and all suspender cables must be brought to a specified strain individually for the main cable voltage. A fasteners on the western tip are used to balance the tension between the single main cable parts.
Suspension of the suspender cable is done gradually. The level of tension at various stages and tension sequences is very important for this procedure.
Beginning in 2011, the right balance between the main cable running and the suspender cable and the proper voltage applied to the main cable and suspender. On November 20, 2012, this process is completed which makes the SAS part of the bridge self-sufficient. After that, the forgery was removed.
Transitional Yerba Buena Island Structure
The Transitional Structure of Yerba Buena Island (YBITS) is a flyover that bridges the gap of the SAS range to the Yerba Buena Island tunnel. Just like Oakland Touchdown on the other side of the new bridge, this bridge section is also a final segment, meaning that the purpose of this segment is to transition sections of existing bridges to the main span of the new bridge. Its linking structure transitions the new bridge-side roads to the upper and lower decks of the YBI tunnel. By mid-February 2012, the northern structure has been poured and the formwork is being removed. In early September 2012, falsework was removed, modified, and built on the eastward site with the completion of the formwork now allowing reinforcement and concrete placement.
Design column
There are a number of columns that support the structure. When the ground level rises from the shore to the Yerba Buena Tunnel level, the height of the ground portion above the column varies. Because this supportive rock structure is hard shale, it will be normal under previous engineering methods to simply dig a relatively shallow foundation for each column, with structural lengths varying progressively. Modern seismic analysis and computer simulations reveal problems with such designs; while long columns may flex several legs at the top (0.6 meters, more or less), shorter columns tend to break, because the rigid deck structure causes the same amount of motion at the top of the column, imposing more bending stress per unit length in shorter columns. This problem is solved by creating columns of the same length (but not uniform), with the "shorter" columns extending on the permanent open shaft to the deep foundation. This allows all columns from YBITS to respond in a fairly uniform way. The space between the columns and the holes is covered by protective protective cover, forming a type of base insulation system at a more sensitive column location. In addition, the western landing of YBITS is a zero moment hinge, so there is no vertical bending pressure at that point.
Construction techniques
Proses konstruksi untuk membangun struktur ini terdiri dari beberapa langkah, ditunjukkan di bawah ini:
- YBITS Construction
The first step is to build a large column foundation that will support the elevated elevated highways from YBITS. Column boosters above the class are constructed and covered with formwork and concrete poured. After pickling, the formwork is then removed. The next step is to build the road itself. The span is thrown on the spot, using a broad reinforcing, with post-strain cable tendon. The highway consists of a hollow box structure, in place in part using formwork, because of both complex shapes involved and the necessity of maintaining the flow of traffic on adjacent structures during construction.
The following sequence is applied to any range between columns:
- Since wood or metal shapes that support concrete casting are increasing, their shape is supported on counterfeiting, in this case using vertical pipe parts, steel beams, and diagonal cables. A wooden deck was then erected on top of falsework to support the lowest forming surface.
- Strengthen for the lowest surface of the box structure is then added, and the concrete is poured.
- During initial castings, strengthening and formwork for the interior sliding beam and each tendon channel is inserted. Then, pour other concrete done.
- Then the interior formwork to support the top surface (deck) is added and the rebar-reinforcement process is repeated.
- After the concrete is drained enough and each tendon is tightened, formwork and falsework are removed, leaving only a concrete surface.
land ramps
In addition to the road leading west, the ramps connecting the bridge traffic to Yerba Buena Island and Treasure Island are inadequate to handle traffic for future expected housing developments. Specifically, the eastern toll road is always very dangerous, while adding west direction to road traffic will disrupt the traffic flow of the bridge. Among the western portal of the tunnel and the existing western suspension range, there is no room for modern ramp configurations. This development is expected to add about three thousand residents to the island, as well as business and office space. To support this traffic, a new ramp-up system (currently only partially completed) will be built on the eastern side of the islands to be connected to YBITS, where there will be enough room for the right mix of traffic and departure. The eastern side of the ramp is estimated to cost around $ 95.67 million as they begin construction in late 2013 for the opening of June 2016. A new westward and take-off lane opens on October 22, 2016.
Exposure
Skyway and YBITS structures have special lighting using 48,000 high-performance LEDs that are grouped in 1521 fixtures, mostly mounted on 273 poles. This equipment is designed by Moffatt & amp; Nichol and built by Valmont Industries. In a special fixture, the radiant pattern of each LED is limited by the masking structure. Each fixture has been independently adjusted and masking LEDs will light up the road only in the direction of travel, similar to vehicle lights and therefore greatly reduce the glare presented to the driver. This is expected to improve safety for travelers. The main highway lane is illuminated by a downward-pointed LED fixture mounted on the main cable saddle. Additional decorative lighting that faces upward on the extreme outer edge of the highway illuminates the suspender cable and the bottom of the main cable. Additional lights highlight the main tower.
- Image illumination
These lights use about half the strength of the old bridge lights and will last about 5 to 7 times longer. They only need to be replaced every 10 to 15 years (compared to every 2 years with old eastern ranges), reduce costs, improve worker safety and reduce the inconvenience of tourists due to the closure of the track.
Removal of old range
The first phase is removing a double balanced cantilever range. Of the several alternatives available the method of dismantling is selected over an option involving destruction by explosives. In this process the bridge was dismantled, removing individual pieces largely in reverse order from the original construction. This requires the construction of a temporary support structure as used in the original construction. Concurrent efforts eliminate the temporary S curve that allows completion of new bike and pedestrian paths and improved approaches of vehicles bound to the east.
Demolition is delayed by the presence of nooking nesting birds. In mid-November, the main part of the west cantilever (left) and the tower had been almost completely eliminated and temporary support was established under the right eastern cantilever. As of May 2015, only one-third of the far right-left is left and on June 12, 2015 the task is completed. On November 14, 2015 the concrete cellular foundation of the E3 dock (which supports east cantilever towers) is explosively destroyed by falling debris. into the steel caisson under the bottom of the mud bay. Many simultaneously detonated charges and versatile air bubble blinds are used to reduce undersea shock waves to protect marine life. For details on the CalTrans E3 removal plan, see this link
The second phase, which is currently underway, involves the removal of five truss and truss causeway ranges with the third and final phase being the displacement of the underwater foundation.
Because the old East Span was disassembled, materials removed from the structure were loaded onto the barge and sent for recycling.
The complete removal process is described at http://baybridgeinfo.org/demolition.
Park gates and fishing docks proposed
A park has been proposed that will allow bay access and it will include a fishing dock. Considerations for expected sea level rise in the middle ages have been proposed by the Gulf Conservation and Development Commission. Improvements to this proposal include retention of some of the foundations of the old approach, this to support pedestrian docks for bay and bridge observations and for fishing. The use of the three foundations is projected to save up to three million dollars of underwater disassembly costs.
Driving experience
In both directions, the driving experience has been greatly improved. In addition to the wider traffic routes in each direction, there are now ongoing tracks for emergency vehicles or defects on each side of the five lanes of traffic. The bridge night lights are now glare-free and new white LED lights have been installed at the bottom of the tunnel that leads to the east. The removal of the sharp curve east of the tunnel has pushed the flow of eastward traffic more smoothly to the west, and through the tunnel, even when compared to the pre-construction configuration.
Pedestrian path
This range includes new pedestrian and bicycle routes, officially named Alexander Zuckermann Bike Path . The line is named in memory of Alex Zuckermann, founder of the Easy Bay Bicycle Coalition and a supporter of Bay Bridge Trail. New pedestrian and bike routes connect the East Bay to Yerba Buena Island. Currently, MUNI is the only public transport carrying bicycles and pedestrians from Yerba Buena Island and Treasure Island to San Francisco. The complementary route in the western landscape to San Francisco is on track for completion by 2025.
Construction incident
Produce controversy
On April 6, 2005, the FBI announced an investigation into allegations by fifteen former welders and inspectors on a new range that welders were rushed to levels affecting their performance in up to one-third of the welds, and that workers were ordered to cover up the damaged welds with re-welding in a shallow manner. Many of these welds are then embedded in concrete, some underwater.
A spokeswoman for the Department of Transport of California (Caltrans) quickly responded with a public statement that it is impossible for defective welding to be hidden from Caltrans inspectors. These were then tested by radiological, ultrasonic and microscopic examinations of some of the welds that were accessible and suspected deficiencies. On April 21, 2005, news reports indicated that the Federal Highway Administration hired a private inspector to remove a 300 pound section (136 kg) for detailed laboratory analysis.
On May 4, 2005, the Federal Highway Administration said testing by three independent contractors showed that the attractive welding of three pieces of steel weighing 500 pounds "" met or exceeded the required specifications. "Since some of the material released for examination was specifically identified by the welder's complaints as worthy of review, these findings were accepted as good news.
Potential foundation problems
In early November 2011, the Sacramento Bee newspaper reported and analyzed various reports (including a whistle blower statement) about the potential forged fake inspection reports relating to pile foundations, including some that support the SAS main tower. The article, and the Sacramento Bee article published on May 26, 2012, provides details on construction and testing concerns and cites relevant engineering experts who ask questions about the adequacy of Caltrans testing and supervision, and construction and testing practice of bridge builders. On June 12, 2012, shortly after publicly endorsing further studies concerning concerns raised in the May Bee article, Caltrans issued a press release with a letter attached to Bee's Executive Editor of Caltrans Director Malcolm Dogherty. The letter includes a request for full retraction of the article, this after affirming a number of technical refusals and special criticisms of the language and tone of the article. On June 24, 2012, Joyce Terhaar, Bee's Executive Editor, responded to the defense of the newspaper's articles and missions. Caltrans also responded with an almost hourly video presentation.
On August 4, 2012, The Bee reported on an ongoing study by Caltrans engineers, who were examining the foundation testing for the agency. The team of engineers, called the "GamDat" team by Caltrans, found new evidence of questionable data related to the tower foundation testing. Following Bee's article, the California Senate Transportation Committee requested the State Legislative Analysts Office to convene an independent expert panel to examine concerns about the SAS tower foundations, and to report its findings. The report is expected to be released in spring 2013.
The Sacramento Bee published more articles on June 7, 2014.
Crash damage
The three-inch (7.5 cm) diameter bolt connects the parts of the bridge deck boss to some concrete columns. There are 288 bolts of varying lengths. Bolts are tested in place by overtightening their retaining nuts. Within two weeks of this tightening, 30 of the first 96 bolts loaded failed. These bolts vary in length from 9 to 17 feet and the initial failure is associated with hydrogen embrittlement, with hydrogen introduced during manufacturing or electroplating. Some bolts can be replaced while others can not be moved and cargo transfer will require more complicated remediation methods. Initial refinements are not expected to delay opening, but then it is believed to delay opening until December. Improvements can cost up to five million dollars. Temporary improvements announced on August 15, 2013, with the opening revised back to the original date. The preferred solution is to add a safe-tendon saddle at each deck boss location. It is recommended internally that problems with the main cable voltage may have caused bolt failure.
Retrofit to repair bolt failures was paired on December 19, 2013. The improvements ended at a cost of 25 million dollars, much higher than the initial estimate and cost projection.
Water leak in superstructure attachment
Some bridge components are mounted on the upper surface of the primary structure. Many of these require sealing of water intrusion into the inside of the deck box. Incorrect sealant applications under the barriers to load traffic on bridges have been found to allow entry of water into the interior. Interior humidity has caused destructive corrosion, which must now be repaired.
Hold grouting trunk failure
The steel support structure is attached to a concrete foundation with a threaded steel rod in the channel. This channel should be filled with concrete grout after installation. Some of these cavities are temporarily closed at the top with a concrete seal. Then the workers misinterpreted some of these locations as grouting when they were just sealed at the very top. Incomplete grouting can cause sea water intrusion that will accelerate corrosion in these critical stems. It is planned to create a small hole in grouting to determine which locations require additional or alternative grouting, oil injection or similar materials, to remove any water.
The automatic welding procedure used by the deck box closure (Shanghai Zhenhua Port Machinery Co. Ltd.) is often done in the rain. Such welding has long been known as leading to the imperfect painting of welds. The weld is considered by Caltrans management to be a low criticality in this bridge due to the compressive force imposed on the deck structure by this particular design. There were also reports of vendors uncooperative with the concerns of Caltrans inspectors and engineers. Due to the fragility of old cantilevered structures and possible destructive earthquakes, Caltrans feels motivated to avoid further delay in the completion of new landscapes.
At the end of January 2014, a Contra Costa Times article reported the results of an investigation of the California State Senate transportation panel. The panel's report is entitled "The San Francisco-Oakland Bay Bridge: Basic Reform for the Future". This preliminary report, written by a contractor to the committee, stated
This is the finding of this investigation that there appears to have been chronic efforts to keep many of the security charges seriously silent, overriding and not being dealt with openly, the ways business is in the public interest.
Other leading California newspapers, Sacramento Bee , reported on July 31, 2014:
A California Senate report released Thursday said that Department of Transport managers "choked and dumped" at least nine top experts for the new San Francisco-Oakland Bay 6.5 billion Bridge after they complained about substandard work by Shanghai, China, the company that builds many of that range.
Full report preliminary report released in January 2014 can be found on this site:
Caltrans's initial response can be found here.
The State Senate investigation resumed in August, with the threat of criminal prosecution addressed to Caltrans.
See also
References
External links
- The Bay Bridge Project's official website, Caltrans
- Calendar Bay Bay Calendown project report index
- San Francisco-Oakland Bay Bridge East Span Caltrans Seismic Safety Project
- Bar Cultivation: Design a New East Range of Bay Bridge ScienceBlog
- The Making and Opening of the San Francisco Bay-Oakland Bridge: A Case in Megaproject Planning and Dissertation Decision Making by Karen Trapenberg Frick, Doctor of Philosophy in Town and Regional Planning
- Timeline San-Francisco-Oakland Bay Bridge Seismic Retrofit 1929-2004 Prepared for Joint Legislative Audit Committee
- East Span Replacement Timeline 1997-2013 Metropolitan Transport Commission
- "The Bridge So FarÃ, - A Suspence Story" A 2006 documentary that records delays in construction
- "Building Your Own Biggest Suspension Bridge in the World" Wired.com
Construction videos
- The New Bay Bridge: Makeover Earthquake
- San Francisco-Oakland New Flying Bridge
- Computer Simulation Sequence Sequence
- Bay Bridge in an Earthquake
- Labor Day Weekend Construction (2009)
- San Francisco-Oakland Bay Bridge East Span Construction (June 28, 2010)
- New San Francisco-Oakland Bay Bridge Built (June 8, 2011)
- SAS and YBITS Construction Progress (June 8, 2011)
- Creation Time of San Francisco-Oakland Shadow Bridge (Published August 30th, 2013)
Source of the article : Wikipedia
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