Main span Eastern span replacement of the San Francisco–Oakland Bay Bridge

1 main span

1.1 s-curve construction
1.2 sas falsework
1.3 deck placement

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.