I N T E R A C T I V E A new Boston landmark
The Leonard P. Zakim Bunker Hill Bridge opens to northbound traffic on Sunday night. The $105 million structure is the widest cable-stayed bridge in the world,
as well as the first "hybrid" cable-stayed bridge in the United States, using both steel and
concrete in its frame. It may also have the longest name in the world, memorializing both the
Battle of Bunker Hill and late civil rights activist Lenny Zakim.
(Graphic by Ed Wiederer / Globe Staff)
Mouse over the red highlighted labels to read more about each part of the bridge.
Concrete box
The north and south spans
of the bridge are made of
cast in place, post-tensioned
concrete.
North Tower266 feet above deck,
322 feet total height
The hollow concrete towers were
cast in place, with walls ranging
from 1 to 4 inches thick.
Cables
Typically, cable-stayed bridges
tension the whole cable at once. Here,
in the first use of the technique in the US, the
cables were iso-tensioned, meaning each strand
was tightened individually with a small hydraulic jack.
Natural light
Holes in the center of the
bridge allow light to filter
through to alewife swimming
up the river to spawn.
Globe Staff Photo / Pat Greenhouse
Steel skeleton
Steel girders and beams frame
the bridge's main span. Two
additional lanes, serving
northbound traffic from the
Sumner Tunnel and North End,
are cantilevered on steel beams
from the east side of the bridge.
South Tower266 feet above deck,
295 feet total heightBalancing act:
Steel boxes built into the
spires anchor the cables to
the towers, right. To keep the
cantilevered section from
throwing the entire structure
out of balance, the cables are
shifted 3 inches off center.
Orange Line
Both of the bridge's towers are
supported by 8-foot diameter steel-reinforced
shafts, drilled into bedrock.
The MBTA Orange Line passes within 6 feet of the
shafts under the south tower. The supports closest
to the subway tunnel are surrounded by 9-foot
diameter steel tubes, allowing the shafts to move
a full 6 inches without damaging the tunnel.
Spline beam39 feet, 10 inches
Extension carries the last
three cable anchorages. The
last cable cleared the old
highway ramp by just 2 feet.
North Tower
South Tower
