The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1935-04-26

of the suspension span, more than twice that Of
any previously attempted and the difficulty Of
erecting foundation for the tower to support
the south span because of the depth Of the
water and the swirlng of the tide in the open
ocean waters at the Golden Gate.
But 1000 feet offshore at depth of 100 feet
adequate foundation formation was discov-
cred although the water here is constantly tur-
bulent because of the seven-mile an-hour tide
which constantly sweeps in and out through the
Golden Gate. At times breakers 20 feet high
crash this point First it was necessary to
level off the site for this pier by blasting rock
over an area of approximately an acre under
water, after which the rock was dredged up,
carried out and dumped in the sea.
Construction of the pier the first ever attempt
ed in the open ocean swept by the tides, was
made possible only by the erection of a giant
concrete fender, $50 feet in circumference,
around the pier site, an original idea never be-
fore tried. This fender Is being built in sections.
First huge steel box is lowered into place on
the bottom, after which it Is bolted to adjoining
boxes by deep-sea divers, working in complete
darkness Then concrete is poured into the boxes.
Gradually the structure is built up until its top
rim is fifteen feet above high water. The east
wall of the fender is omitted above elevation
until the enormous caisson, to be sunk and
filled with concrete for the pier itself, is oated
will be completed, and the builders will have
quiet water unaffected by tides inside the fender
in which to complete the pier. The fender will
serve as permanent protection to the pier when
the bridge Is completed.
Meantime, the Marin tower, built on solid rock
above the water line, was completed ahead Of
program. Its slender steel columns rise above
foundation of concrete, embedded in the rock.
The tower Is of cellular steel construction, the
inside hainO a workable 1ahvripth Of ham
In which even the designer could be lost without
his charts. Steel ladders connect the hundreds
of chambers from the foundation to the top of
the tower, 746 feet high.
The twin anchorage blocks which support the
weight of the worlds longest suspension span
are enormous solid concrete masses, weighing
$1,000 tons each, constructed that they push
against solid rock when supporting the cables.
The cable pull at each anchorage is 100000
pounds, but the anchorage block has resistance
sufficient to support two Golden Gate bridges.
Between the piers and the anchorage blocks are
supporting pylons for the cables and the bridge
itself.
Possible effects of earthquakes were an impor-
tant consideration in designing the Golden Gate
bridge. The bridge will withstand an earthquake
far more severe than any temblor ever felt in
California. Because of the fexibility of the sus-
pension type of bridge, the structure is far bet
steeframe Office buildings.
Wind velocity through the Golden Gate during
storms could sway the middle part of the center
span much as 20 feet without damage With
wind velocity of 80 miles an hour, the bridge
has safety factor Of &c. The strongest wind
on record at the Gate is SO miles. more
serious engineering consideration was the effect
of heat and cold. Expansion and contraction due
to the sunshine and darkness may raise and low
er the bridge as much as 10 feet on hot days.
Golden Gate bridge will have six highway
lanes, from curb to curb. Outside the curbs will
be footbridge, 10h feet wide on each side of
the roadway. At its center, the bridge proper
will be 220 feet above the water. Construction
has progressed to a point where the engineers
have definitely scheduled completion of the
bridge for the fore part of 1887 and the com-
pletion of the entire bridge project will be cele-
brated by an international exposition the fol-
lowing year.
One other item in regard to these two great
est bridges is worthy of mention That is the
great cost. The total cost of the Golden Gate
bridge will be approximately S33, 100000 to be
paid for by a bond issue for S35OO0OO0 author
lied by the six counties of the Golden Gate
Bridge and Highway district. 1t is self-liquid-
ating enterprise and the total cost will be paid
In less than 80 years from tolls collected. The
Bay bridge will cost some S76eO0OOO of which
, Approximately S60,000,000 is being underwritten
by the Reconstruction Finance corporation.
Some S10,000,000 more represents the cost of
railway installations and the remaining S6600,-
600 is the cost of the approaches to the bridge,
which is to be taken from the gas tax funds
allotted to the northern California counties ant
which must be returned to the state out of tolls
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