Da
Vinci’s
Tools
of
WarThe Diving
Suit /
Leonardo
designed an
early diving
suit, which
he hoped the
Romans could
use to disable
enemy ships.The
Parachute /
The inventor
drafted designs
for an early
parachute
made of wood
and linen.
Skydiver Adrian
Nicholas put
the chute to the
test in 2000.Armored
Vehicles /
A far cry from
today’s war
machines,
Leonardo’s
wooden tank
would have
been powered
by two men
operating a
crankshaft.Crossbow /
In 1486,
Leonardo
designed a
giant crossbow
that would
employ a
crank and
gear system
to launch
projectiles.1777
Construction on the
world’s first cast-
iron bridge begins in
Coalbrookdale, England.
Thomas Jefferson was so
enthralled, he ordered an
engraving of the bridge.1841
Jacques Triger invents
the pneumatic caisson,
allowing workers to
dig pier foundations by
pumping compressed
air into a chamber.1874
The world’s first steel
truss bridge, the Eads
Bridge in St. Louis,
Missouri, is completed.1883
Emily Warren Roebling
unveils the Brooklyn
Bridge. Designed by
her father-in-law, John
A. Roebling, who died
before it was finished, the
bridge was the longest
suspension bridge at that
time, with a main span of
1,595.5 feet.1937
Construction wraps on
San Francisco’s iconic
Golden Gate Bridge.2011
The world’s longest
bridge, the 102.4-mile
Danyang–Kunshan
Grand Bridge in China,
is completed.480 B.C.
The Greek historian
Herodotus details
the construction
of Xerxes’ pontoon
bridges, rope-tied
floating barges
strung together
during the Greek
and Persian War.1ST CENTURY A.D.
The Romans finish
construction on the
Pont du Gard bridge
in France. The solid,
triple-decker stone
arches still stand
today.1464
Tibetan engineer
Thangtong Gyalpo,
who built simple
suspension bridges
throughout Tibet and
Bhutan, dies. The last
of his bridges washed
away in 2004.A BRIEF HISTORY OF
BRIDGE CONSTRUCTION
▶ which Leonardo would have
been familiar, his design relied
solely on the forces of physics
and gravity with no need for
fasteners or mortar. Critically,
the design also included wing
walls, or abutments that splayed
out on either side, which would
have steadied the bridge against
high winds.
Strong winds have forced even
relatively modern bridges from
the 20th century—such as Gal-
loping Gertie, the famed swaying
bridge in Washington State—
into lateral oscillations, which
cause the bridge to sway back and
forth and can lead to collapse.
The inventor didn’t spec-
ify what materials he would
use. So, based on the materi-
als and technology that would
have been available at the time,
Bast and her colleagues figured
stone was the likeliest choice.
They calculated that wood, for
example, wouldn’t have been
strong enough to hold up a
bridge of that length. Unrein-
forced masonr y structures are
“d r iven by g e ome t r y b e c a u s e
the stone has an incredibly
high compressive strength,”
meaning all the pieces press
tightly against one another
to keep the bridge standing,
Bast says. The team used a
gypsum powder 3D printer to
create each of the 126 blocks,
which needed to be a uniform
weight and create enough fric-
tion to keep each stone locked
in place. It took the 3D printer
one hour to produce each piece.
The crucial moment came
when Bast dropped the final
piece, called the keystone,
into place. “I had to really lock
it in,” Bast says. “That was the
best sign that it was being sup-
ported by the stones around
it instead of relying on the
scaffolding.” Newer, stron-
ger materials and updated
designs have made unrein-
forced masonry bridges all but
obsolete. But one thing is cer-
tain: Leonardo’s bridge likely
would have stood the test
of time.SCIENCE&^SOCIETYPICTURE^ LIBRARY/GETTYIMAGES(DIVINGSUIT,^PARACHUTE);PRINTCOLLECTOR/GETTY^ IMAGES^ (ARMORED^ VEHICLE);ALINARI^ARCHIVES/CORBIS/GETTY^ IMAGES^ (CROSSBOW)20 May/June 2020Science
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