Design and construction Eastern span replacement of the San Francisco–Oakland Bay Bridge

1 design , construction

1.1 skyway viaduct
1.2 main span

1.2.1 s-curve construction
1.2.2 sas falsework
1.2.3 deck placement


1.3 main span tower

1.3.1 tower construction
1.3.2 crowning double cable saddle emplacement


1.4 sas main suspension cable

1.4.1 cable placement


1.5 yerba buena island transition structure

1.5.1 column design
1.5.2 construction techniques


1.6 island ramps
1.7 lighting

design , construction
skyway viaduct

new , old approach spans (may 2008)



cutaway illustration, showing battered piles support skyway



700-ton segment lift

the skyway viaduct connects sas portion of bridge oakland shore. 2007, 75 percent of skyway portion completed. since section crosses shallower portion of bay, foundations constructed within sheet-pile cofferdams. mid-2009, final connection of viaduct portion ground level @ eastern end being finished , pedestrian walkway being attached completed sections.

rather set pilings deep enough reach bedrock, pilings founded in firm archaic mud below soft mud deposited distant placer mining in late 19th century. since archaic mud weak in concentrated load application conventional vertical friction piles, large diameter tubular piles driven (inside pumped-dry cofferdams) @ angles, forming battered (splayed) footing, through archaic mud firm aggregated sand, mud, , gravel of alameda formation. long pilings needed, segments welded completed segments installed.

when pilings in place, reinforced concrete pad poured @ bottom of cofferdam form footing column, subsequently cast in place around rebar using reusable metal formwork.

a single viaduct segment located on each column cast in place using forms. pairs of precast span segments, fabricated in stockton, california, barged location , lifted place specialized cantilever lift. (cantilever lifts, counterweights , other equipment , materials lifted either barge crane or jack-up crane located between adjacent columns.) once in proper location, opposing segments joined through tendons (cables within conduits tensioned jacks), forming balanced cantilever on column. eventually, gap in spans between columns closed, forming tendon-reinforced beam.

the oakland touchdown curved elevated roadway connects skyway oakland shore (the beginning of bridge). curve required bring alignment of existing ground-level approach road. yerba buena island transition structure (ybits) west of main span, section end segment of new bridge , being constructed @ same pace ybits. construction process consists of 2 phases, first phase completed (westbound traffic side). eastbound touchdown not completed until existing roadway out of way. done constructing gentle swing south touchdown may completed. first stage of work move eastbound traffic south completed minor traffic delays during 2011 memorial day holiday (may 28–30). driving experience has been improved, without problems came infamous s-curve. second stage move westbound traffic space made available required construction of elevated approach. completed on february 19, 2012. designed procedure expected save time in total effort, speeding completion of span. oakland touchdown completed in march 2013.

on three-day weekend beginning 8:00 pm friday, february 17, 2012, westbound lanes shut down allow connection of approach roadbed new temporary structure. execution of task dependent upon weather, dry conditions being required re-striping lanes, , not determined until few days before work done on weekend. scheduled completion 5 a.m. on tuesday, february 21, work completed 34 hours ahead of schedule, , opened traffic @ approximately 7:15 p.m. on sunday, february 19.

main span

the principal span of seldom-built type, self-anchored suspension bridge. unique in being both single tower , asymmetrical, design tailored site. ship channel clearance, bridge require @ least 1 long span, while ready access bedrock found close yerba buena island. 2 tower cable-stayed design require deep tower footings, , conventional 2 tower suspension bridge additionally require massive anchor built in deep bay mud. curved nature of approach places additional constraints upon design.

while earlier bridges of type use chain eyebars, long span needed here uses wire cable, other modern suspension bridges. uniquely, single loop of cable rather usual pair of cables, and, rather being spun in place above catwalks, substantial bundles of strands dragged place temporary support above catwalks, suspended tensioning strand. these strand bundles arranged compacted form completed main cable.

july 31, 2009: first eastern main span support partial truss falsework beyond

being asymmetrical, shorter western span must pulled down against forces imposed longer eastern span. in order avoid uplift in supporting columns, span terminated massive concrete end weight. end weight carries turning saddles main cables. seen in northwest corner image above, there upward component tension force provided main cable, , component removes of weight of end cap columns. (the greater, horizontal, component countered compressive forces exerted box deck structure characteristic of type of bridge.)

the segments of each of 2 deck spans retained in compression during severe earthquake post-tensioned internal tendons joining extreme end caps, carried internally in cable trays. these tendons required since eastern end support both lighter western counterweight , soil conditions radically different @ each end, western end being founded in bedrock shale while eastern end, vertical supports driven bedrock, contained within softer mud deposits, respond more actively seismic shocks shale. intent combination of tensioned tendons , compressive roadbed box structure keep 2 end caps in same relative position.

the bridge segments @ each end not simple repetitions of central span segments. extreme deck segments on eastern end curved , tilted fair curved portion of skyway. these extreme segments beyond main cable strand anchors , eastern support columns , substantial portion of bridge joining skyway in place (the grey portion seen above). extreme east bound deck segments on western end must fair horizontal eastbound portion of ybits connector, while westbound (north side) segments begin rise westbound ybits, elevating traffic upper deck of yerba buena tunnel.

s-curve construction

the old cantilever bridge connected yerba buena tunnel double-deck truss causeway included curved section. structure occupied area must clear new bridge approach, necessary construct entirely new, temporary approach old bridge. required swing south clear area new construction, , north more severe curve connect cantilever. there few days available during bridge shut traffic, curved portion built adjacent final position on trestle extended beneath , beyond old curved connector. during replacement, old section jacked out of way (to north), , new section jacked place.

s-curve images

on september 3, 2007, first section associated construction of new east span, 300-foot (91 m) temporary span connecting main cantilever section yerba buena island tunnel, put service. construction of new connector span started in 2007 alongside existing span. caltrans closed bay bridge during labor day weekend crews replace old span. once old section removed, new span rolled place using computer-guided system of hydraulic jacks , rollers. new section secured place , bridge re-opened 11 hours ahead of schedule, morning commute on september 4, 2007. in september 2009, during single holiday closure, new temporary steelwork route traffic around location of final approaches new bridge put in place, , connections tunnel exit , existing bridge completed, done in september 2007. bypass enabled construction of permanent transition structure between double-deck tunnel exit , new side-by-side bridge structure. upon completion of bridge, extended closure allowed removal of temporary structure , completion of road link.

all of sections of old span on yerba buena island (around s-curve routes traffic) dismantled, , supports new span being built in location.

the s-curve site has become known accidents, fender-benders fatal plunge. wrecks typically occurred during non-commute times, when traffic flows faster, @ or above general bridge limit of 50 mph. additional signage , visual , physical indicators indicating 40 mph s-curve speed limit installed following major accident. upper deck speed advisory @ curve posted 35 mph , improved system of rumble strips installed.

sas falsework

falsework parallel truss bridges temporarily supporting deck segment box structures

the entire deck structure must supported in precise alignment until:

the end caps anchors , turning , tensioning saddles complete.
the tower main cable saddle complete.
all deck segments in place , joined.
the internal tendons placed , tensioned.
the main cable spun.
all suspender cables in place , adjusted tension.
the main cable tension balanced on each side. (this maintained suspender cables tensioned.)

the falsework perform task pair of substantial truss bridges, prefabricated in segments, columns , span segments lifted place barge cranes. trusses supported on foundations consisting of or built atop driven piles. upon completion of bridge, entire falsework structure , exposed underwater supports removed make safe channel deep draft ships transiting , port of oakland.

deck placement

by late august 2009, temporary column work complete, truss spans in place , prefabricated sections being placed upon it. giant barge crane, left coast lifter, used place 28 main deck box structures. major segment placement on sas section of bridge completed in october 2011. on october 19, 2011, small gap between sas deck , curved skyway extension closed east-bound side, , west-bound gap closed following week. november 2011, deck placement of sas span complete, making 1½ miles of continuous roadway.

in july 2013, entire sas span completed , asphalt paving roadway began. each deck segment paved 2 single-inch layers of asphalt , concrete should durable , last entire lifetime of bridge. however, rest of bridge not paved asphalt instead received protective coating finish.

main span tower

first stage tower segments showing cross section , attachment methods. lower external gray areas covered sacrificial box structures ( mechanical fuses ), while upper covered external flat plates numerous fasteners join segments.

the design employs extensive energy absorbing techniques enable survivability , immediate access emergency vehicles following maximum creditable earthquake (mce), estimated @ 8.5 moment magnitude in 1500-year time span. rather designing rigidity, instead flexible structure, resonant motion absorbed plastic shear of sacrificial, replaceable components. smaller earthquakes impose elastic stresses on components, higher proportion of plastic (and energy absorbing) stresses in larger earthquakes. design philosophy extends other metal components of bridge, including sacrificial tubular end keys align self-anchored suspension approach structures @ each end.

the tower consists of 4 columns. each pentagonal column consists of 4 tapering and/or straight sections, joined end-to-end external plates , internal stringer finger joints secured fasteners. columns joined horizontally sacrificial box structures. these box joins intended absorb earthquake-induced motion elastic , plastic shear deformation tower sways. under severe earthquake, deformation absorbs energy otherwise lead destructive tower motion, protecting primary structure of span. expected design allow immediate use of bridge emergency vehicles, joins being replaced needed restore bridge original condition. uniquely, tower has no direct connection roadbeds, enough space allow swaying under severe earthquakes without collision.

tower construction

march 4, 2011: phase 4 4 columns in place; jack-up crane (to left) used erect , dismantle scaffold, , gantry crane atop scaffold lifts , places tower columns.

the process build sas tower atop foundation consisted of 5 phases. first 4 phases each consisted of lifting 4 similar columns , bolting them place , elements connecting them, while last phase lift final top cap carry crowning main cable saddle. on july 28, 2010, first of 4 below-deck main tower pillars erected, having arrived earlier in month barge china. placed lifting 1 end barge temporary scaffold, carriage on barge allow lower end move place. after columns bolted place, scaffolding extended upward allow next set of above deck columns erected, lifted, , translated position, process repeated each of remaining phases.

tower erection continued when second set of columns arrived in week of october 24, 2010, 3 months after first set placed. second set of columns erected gantry atop scaffold , placed on first 4 columns placed earlier in year. after columns set place, bolted first set of columns. after second phase complete, tower 51 percent completed , stood @ height of 272 feet. third set of tower columns did not arrive until week of december 15, 2010. third set, larger crane, lifted , placed on second set of columns. tower stood @ impressive height of 374 feet , 71 percent complete. erection process did not continue until following year when final set of tower columns arrived valentine s day 2011. these 4 columns, each being 105.6 feet tall, lifted in week of february 28, 2011 , placed on third set of columns. tower stood @ height of 480 feet , 91 percent complete.

april 15, 2011: grillage in place.

the fifth , final tower phase lift grillage (a structure join columns, more commonly used foundation element) weighs 500 tons, lift main 450-ton cable saddle, , lift final tower head completed entire sas tower. of these final pieces arrived @ site same day fourth set of tower columns arrived. on april 15, 2011, first part of fifth , final phase began. 500-ton grillage lifted 500 feet in air , placed on fourth set of columns. tower stood @ height of 495 feet , 94 percent complete. took 1 day lift , place grillage on top of tower.

crowning double cable saddle emplacement

may 19, 2011: near sunset, cable saddle being positioned before final touchdown.

working entire day of may 19, 2011, operating engineers , ironworkers lifted , placed 900,000 pound double cable saddle atop sas tower. while large portion of span fabricated in china, particular piece made in japan, eastern , western deviation saddles , main cable hydraulic jacking saddle.

this cable saddle guides , supports mile-long main cable on tower placed later in year. in december 2011, deck placement of sas span completed , cable construction progress began. however, few months before in july 2011, tower head lifted , placed on saddle in test fitting , removed allow laying of cable. later on in 2012, cables placed on tower saddle , anchored throughout whole sas span. tower head permanently installed final time, along aircraft warning beacons, completing entire sas tower @ final height of 525 feet (160 m).

sas main suspension cable

compaction test section of sas cable; distinct colors mark individual parallel wire strands, each bundle of 127 pencil-thin wires. there 137 such bundles, each individually terminated @ eastern end of sas.

the tower saddle includes eyebars attachment of temporary cables supported 4 walkways, each simple suspension bridge (called catwalk) allowed access cable spinning mechanism , main cable during construction. in several ways similar ski lift, additional superior cables carried 1 or more of these travelers, wheeled devices shuttled 1 end of span other, pulled drafting cables manipulated several winches.

cable images


















































































































































june 24, 2011: gantry crane has been removed , 2 of 4 temporary catwalks have been installed.

the main span use single cable, spun using pre-bundled groups of wires anchor point @ eastern end of main span, across eastern corner horizontal deviation saddle, on vertical deviation saddle on eastern end, , on corresponding half of main tower saddle, down 90-degree deviation saddle @ western counterweight, across counterweight, passing on hydraulic tensioning saddle, around opposing western deviation saddle, other half of main tower saddle, on eastern vertical deviation saddle down final eastern corner deviation saddle, appropriate anchor point in eastern strand anchor opposite beginning.

as bundle laid down, supported supports mounted on catwalk, both ends attached , cable tensioned @ eastern anchor points. conventional cable suspension span, of tensioned bundles compressed circular shape , protected circular wrap of wire. saddles suspender cables added , suspender cables placed , tensioned. suspender cable tensioning lifted span supporting falsework.

october 1, 2011: tracks within blue cage guide strand hauler around deviation saddle, continue across jacking saddle , around opposite deviation saddle.

in mid-june 2011, preparations spinning of main cable began installing temporary catwalks on sas span. both western catwalks installed , mid-august, 4 catwalks installed in place , approximation of completed outline of bridge seen. 4 catwalks, traveler, suspension cable , drafting cables , winches , specialized tracks @ deviation saddles had in place before strand dragging begin. these catwalks required worker s access cable strands bundling , arrangement individual wires placed.

work in september 2011 included installation of turning tracks travelers @ western deviation saddles. these tracks allowed continuous motion of traveler across western end of main span. mid-october 2011, traveler cables installed. temporary group of tower stay cables west, intended resist overturning forces imposed bare main cable, installed. subsequently, eastern deviation saddles installed, preparing bridge cable placement.

cable placement

the cable construction technique differed used earlier western spans , similar conventional suspension bridges. in method, cables spun few wires @ time, bundles made wires spun pulling loop along cable s route. sas used different technique, wire strands pre-fabricated mile-long cable bundles bundle terminations in place, pulled dragging 1 end through route. after attachment termination, tensioning operation performed on each bundle @ eastern anchor point, , bundles suspended few feet above catwalk. total of 137 such bundles installed. bundles positioned, temporarily tied form cable. cable in place in late may 2012. later compacted circular shape, , wrapped protective wire jacket. in mid-march 2013, western portion completed , catwalks removed. wire wrapping still in progress on eastern portion.

since main cables curve , suspender cables splay outward deck edge, saddle design individual location, being fabricated in mirror image pairs each side. in mid-june 2012, saddles in place upon main cable. wire rope suspender cables draped on these saddles , later pulled outward , attached projections main deck.

on conventional suspension bridge, sections of deck hung in place , tension suspenders. proper initial length of each suspender predetermined engineering calculations , adjustments required segment relative positioning , equality of load distribution amongst several suspenders of section. on bridge, deck sections in fixed relative position (being joined , resting upon falsework) , suspender cables must brought specific tensions individually in order tension main cable. jacking saddle on western end used balance tension among sections of single main cable.

suspender cable tensioning performed in stages. degree of tensioning @ various stages , order of tensioning critical procedure.

starting in 2011, proper balance between main cable runs , suspender cables , proper tension applied main , suspender cables. on november 20, 2012, process completed made sas portion of bridge self-supporting. after that, falsework removed.

yerba buena island transition structure

several construction phases can seen in 2011 image, finished columns falsework erection through formwork completion prior concrete pouring.

left: temporary double deck s-curve (upper deck westbound toward tunnel).

center: southern columns (for eastbound traffic tunnel lower deck).

right: northern columns, falsework, , formwork (westbound tunnel upper deck).

the yerba buena island transition structure (ybits) elevated roadway bridges gap sas span yerba buena island tunnel. oakland touchdown on other side of new bridge, section of bridge end segment, meaning purpose of segment transition portions of existing bridge main spans of new bridge. connecting structure transitions new bridge s side-by-side roadways upper , lower decks of ybi tunnel. in mid-february 2012, northern structure has been poured , formwork being removed. in september 2012, falsework had been removed, modified, , constructed @ eastbound location formwork completion allowing reinforcing , concrete placement.

column design

there number of columns supporting structure. ground level rises shore level of yerba buena tunnel, height of above ground portion of columns varies. since rock structure supporting these hard shale, normal under previous engineering methods dig relatively shallow foundation each column, structural length varying progressively. modern seismic analysis , computer simulations revealed problem such design; while long columns flex several feet @ top (0.6 meter, more or less), shorter columns break, since rigid deck structures cause imposition of similar amount of motion @ tops of columns, imposing more bending stress per unit length on shorter columns. problem solved making columns of similar (but not uniform) length, shorter columns extending in permanent open shafts deep foundations. allows columns of ybits respond in sufficiently uniform manner. space between column , pit covered protective sacrificial cover, forming type of base isolation system @ more sensitive column locations. in addition, western landing of ybits 0 moment hinge, , there no vertical bending stresses @ point.

construction techniques

the construction process build structure consists of several steps, shown below:

ybits construction

the first step construct foundations of large columns support elevated roadway of ybits. above-grade column reinforcing constructed , enclosed formwork , concrete poured. after curing, formwork removed. next step build roadway itself. spans cast in place, using extensive reinforcing, post-tensioned cable tendons. roadways consist of hollow box structures, cast in place in sections using formwork, owing both complex shapes involved , necessity of maintaining traffic flow on adjacent structures during construction.

viewed completed portion of ybits, double-deck tunnel connects eastern , western spans.

the following sequence applied each span between columns:

island ramps

yerba buena island ramps

other current westbound off ramp, existing ramps linking bridge traffic yerba buena island , treasure island inadequate handle traffic future expected residential development. in particular, eastbound off ramp has been extremely hazardous, while added westbound on ramp traffic interfere bridge traffic flow. between tunnel s western portal , existing western suspension span, there no room modern ramp configurations. developments expected add 3 thousand residents island, business , office space. support traffic, system of new ramps (currently partially completed) built on eastern side of islands link ybits, there adequate room proper traffic merges , departures. east-side ramps expected cost $95,670,000 while began construction on late-2013 june 2016 opening. new westbound on- , off-ramps opened on october 22, 2016.

lighting

the skyway , ybits structures have custom lighting using 48,000 high-performance leds grouped in 1521 fixtures, of mounted on 273 poles. these fixtures designed moffatt & nichol , built valmont industries. within specific fixture beam pattern of each led restricted masking structure. each fixture has been adjusted independently , led masking illuminate roadways in direction of travel, similar vehicles headlights , therefore reducing glare presented drivers. expected improve safety travelers. main span roadways illuminated downward-pointing led fixtures mounted upon main cable suspender saddles. additional upward-facing decorative lighting @ extreme outboard edges of roadways illuminate suspender cables , underside of main cable. additional lights highlight main tower.

lighting images




















decorative lighting effect of roadside , main-cable lamps

these lights use half of power of old bridge s lights , last 5 7 times longer. have replaced every 10 15 years (compared every 2 years old east span), reducing cost, improving worker safety , reducing traveler inconvenience due lane closures.