New Bay Bridge East Span Reaches High Point: Cable Pulling Begins
Video: Cable Strand Installation
Looking much like a ski lift, the tram apparatus (whose blue parts are visible in the foreground) will carry the cable strands up the incline to the top of the tower, down the other side and back up and down the other side.
Workers make adjustments to the aerial portion of the tram apparatus.
At the eastern edge of the SAS, the cables will enter a hollow underneath
the deck, splay out and connect to the rows of anchor rods that are
bolted into the deck. Hence the bridge type: self-anchored suspension
span, with the cable anchored into the deck itself, rather than a
Covered for protection from the elements, coils of cable wait on
the SAS deck for their turn on the lift.
One of the cables is placed on a giant spool in preparation for
the first pull, likely on Wednesday.
All photos taken December 19, 2011, by Bill Hall, Caltrans
December 19, 2011
The twin decks of the under-construction new Bay Bridge East Span were buzzing with activity today as workers prepped for the next phase of the monumental project: the pulling of the main cable of the bridge’s self-anchored suspension span (SAS), which will start this week, likely on Wednesday.
Actually, the process involves the pulling of many separate strands — 137 in all. And each of those strands is made up of 127 individual 5 mm, high-tensile steel wires, each strong enough to support a military Hummer. At a briefing for the media today, Caltrans spokesman Bart Ney predicted that the pulling of the first strand could take up to two days. Once crews get the system down, they will pull two to three strands a week, and perhaps pick up the pace even more.
“This is one of the high points in the construction of this bridge,” said Ney. “You can really see the finish line.”
According to Ney, this is the first time that a cable has been placed
in this particular way. The cable will follow the path of the bright
orange cable catwalks that have been visible for several months. Each
strand will be hooked to a device that functions like a ski-lift, hauling
the strand from the anchorage in the eastern edge of the SAS, up and
over the 525-foot tower, and down to the western edge of the decks.
At the western edge, the strand will be transferred to a second pulling
device that will take it around the back side of the bridge; once it
rounds the bend, the cable will be hooked back to the primary hauling
system for the journey back to the top of the tower down to the western
side. The lift will travel at 3 to 5 miles per hour, about the speed
of a person walking. (See simulation.)
between the pulling of each strand, crews will pause to survey the
work at night, when temperatures are cooler, to make sure the strand
is properly in place.
Multiply the 137 strands by the 127 wires in each strand, and it comes
to a total of 17,399 steel wires in the cable. The nearly mile-long
strands will be bundled together and compacted into a solid, 2.6-foot
diameter cylinder that will act like a giant sling cradling the side-by-side
decks. At key points, suspender cables will connect the main cable
to the decks.
The new East Span is a project of the Toll Bridge Program Oversight
Committee, made up of Caltrans, MTC's Bay Area Toll Authority (BATA)
and the California Transportation Commission.
Progress on the cable
installation can be viewed from the new publicly accessible interpretive
display located on Treasure Island and online via construction cameras;
visit BayBridgeInfo.org for
a map to the display and bata.mtc.ca.gov to
access the cameras.