Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1890-03-03
A WONDERFUL WORK.
The Long Cantilever Bridge Over the
Forth River at Edinburgh,
A TRIUMPH OF ENGINEERING SKILL.
One and Five-EighthS Miles in Length, and
so Strongly Built That
1T WILL SUSTAIN $4,000 TONS BURDEN

The Forth bridge at Edinburgh, which is
to be opened tomorrow with great ceremony,
is justly regarded as one of the greatest tri-
umphs of modern engineering skill. One OF
the assistant engineers who worked upon the
great structure contributes to Chambers
Journal of February % the following &C.
count of the bridge. The briefest
glance at the map of Scotland abund-
antly evidences the raison d'etre of the
gigantic structure across the Firth of Forth,
whose successful completion has just marked
SO important an era in the annals of engl-
neering. Various projects had from time
to time been mooted for the bridging of the
firth, but were one by one abandoned. In
1881, however, the North British, Great
Northern, Northeastern, and Midland Rail-
way companies, being anxious TO attain di-
rect communication to the north of Scotland,
which should enable them to compete with
the west coast companies for this traffic on
equal if not more favorable terms, instructed
their respecting consulting engineers, Sir
John Fowler, X. c. NJ g., the late Mr..
Harrison, and Mr.. Barlow to report on the
matter.
On the 4th May, 1881, these engineers
submitted joint report, the result of pro-
longed consultations, unanimously agreeing
that the steel cantilever bridge designed by
Sir John Fowler and Mr.. B. Baker fulfilled
all the necessary conditions, and was the
least expensive and most suitable design for
bridging the Firth of Forth. The Forth
Bridge Railway Company accordingly ap.
pointed Sir John Fowler and Mr.. B. Baker
as engineers for the undertaking;
and by the close Of 1882 the con-
tract was let to the combined firm of
Messrs. Tancred, Arrol & Co., who forth
with commenced active operations.
WHAT A CANTILEvER is.
Before passing to the building OF the
structure and the manv points of interest
Herewith connected, we propose briefly to
deal with the principle of The cantilever
and the general features of the bridge itself.
The word 'cantilever,' which denotes a
bracket, is becoming rapidly popularized.
In the Forth bridge, as will be seen from
the annexed diagrams, the brackets are
double, being placed back to back and
fastened together. No better illustration
of the cantilever principle can be
given than that of Mr.. Bakers
human cantilever'-namely, two men
sitting on chairs, with extended arms, and
supporting the same by grasping
sticks butting against the chairs
In the Forth bridge the chairs must
be imagined to be placed third of a mile
apart, and the mems heads to be $50 feet
above the ground. Their arms are repre-
sented by huge steel lattice members, and
the sticks or props by steel tubes II feet in
diameter and one inch and quarter thick.
No novelty is claimed for the cantilever
system. 1t is, as a matter of fact, prehis- |
toric arrangement, as illustrated in the |
stone corbel and Intel combinations found |
in the earliest Egyptian and Indian tenn
piles.
Passing on to the leading dimensions of |
the Forth bridge, the total length of the |
structure is s, 296 feet or nearly 15s miles; |
and there are two spans OF 10 feet, two of |
$50 feet 15 approach viaduct spans of 16S |
feet, four granite arches of 81 feet span on |
the south shore; with three arches of
similar construction and % feet span |
at the corresponding northern abutment. A
clear headway of $50 feet at high water |
spring tides is allowed. The extreme height |
of the structure is 361 feet above high water, |
the greatest depth of the foundations being |
about 80 feet below the same level.
HUGE PILES OF MASONRY.
The main masonry piers, three in number,
situated respectively on the south shore, on
the island of Inchgarvie (an island fortuit- !
ously placed midway between the two deep |
chsnnels), and on the Fife shore, consist |
each of group of four masonry columns of |
concrete or rubble faced with granite, and |
40 feet in diameter at the top by Sc feet |
high; resting either on solid rock, as in
the case of the Fife and two northern Inch
garvie piers; or on caissons filed with con-
crete, as in the case of the two southern
Inchgarvie and the Queensferry piers.
The masonry abutments at each end of
the bridge call tor no special remark, and
may be here dealt with. Their dimensions
have already been given. The founda-
tions were in the dry, and presented
no features of difficulty. The piers and
arches were built of granite brought
from the weil-known quarries at Aberdeen
direct to the site by sea. Upwards of d.
600 tons of cement, 7O7, 900 cubic feet of
granite, and III, 900 cubic feet of masonry
and concrete were employed in the tounda-
tions and piers; while no less than one
million cubic feet of timber were used for
temporary purposes.
While the foundations and masonry had
been proceeding, steady progress had been
maintained in the workshops in
the materials for the can
tilevers. Visitors to South Queensferry