)
sulting from blast on the exposed
side of the building.
The Public Utilities
In Nagasaki the public utility
system was comparable to that in
an American city of 30,000 popula-
tion except that open sewers were
used. Damage to the water supply
essential for fire fighting was of
the
greatest
significance.
This
was not caused by failure of the
underground mains, but by loss of
pressure through breakage of pipes
in houses and buildings.
Earth surface depressions up to
one foot in depth were observed at
scattered points in a filled-in area
at a maximum distance of 2,000
feet from ground zero.
This caused a series of failures
of 12-inch cast-iron water pipes
three feet below grade, the breakage probably caused by an unequal
vertical displacement. There was
no serious damage to reservoirs
and water-treatment plants because they were at too great a
distance.
Utility poles were destroyed by
blast or fire, and overhead utilities
were heavily damaged at distances
up to 10,000 feet. Underground
electrical conduits were little affected. Switch gear and transformers were not damaged directly
by blast but by secondary effects,
such as collapse of the structure in
which they were, or by debris. Motors and generators were damaged
by fire.
Gas containers were
heavily
damaged by blast at 6,600 feet and
the escaping gas was ignited, but
there was no explosion. Gas mains
suffered no observable damage.
Street railway equipment was
heavily damaged by fire and blast.
Buses and automobiles were, in
general, also damaged by blast and
were burned out at shorter distances. As an example, an American made car was heavily damaged and burned at 3,000 feet,
while one at 6,000 feet suffered
only minor damage.
tent
for
shelter,
many
although
timber,
)
tance of 900 feet, and none was
damaged beyond half a mile.
Bridges made of wood were
burned in most cases, but the steelgirder bridges suffered little dam-
age,
from
One bridge,
ground zero,
only 260
feel
which was a
girder type and had a reinforced
concrete deck, showed no sign of
any structural damage. It had apparently deflected and rebounded,
causing a slight movement.
Other bridges at greater dis-
tances suffered more lateral shifting.
was
A
reinforced-concrete
lifted from
steel girders of
the
deck
supporting
one bridge,
pre-
sumably because of the reflected
blast wave from the water below.
While the destructive effects observed in Japan are comparable in
general to those to be expected in
the United States, there are some
differences. There is also the question of damage to the large bridges
of many American cities for which
This is because of the fact that,
with usual design stresses, the
work necessary to produce failure
in steel is greater in proportion
than in reinforced concrete. Conse-
quently, tall buildings with heavy
steel frames, constructed so as to
provide good continuity at connections, and a iong period of vibration, should withstand the effect
of blast quite well.
especially vulnerable to blast damage.
average six-story, reinforced concrete, frame building this would
be roughly equivalent to 2 per cent
of the vertical load.
On this basis, American reinforced-conerete buildings would be
much less resistant to collapse
than those designed for earthquake
resistance in Japan. However, no
firm conclusions can be drawn on
this subject, because most American buildings have lateral strength
far more than that required to
withstand a fifteen pounds per
square foot wind load.
Requirements in West
In the eleven Western States of
this country, the building codes
highest requirements.
The design specifications, as
stipulated im the building codes,
are similar to those for wind loads,
with a 33 per cent increase in the
206
forced concrete buildings, except
that steel has a somewhat freater
energy absorption capacity than
reinforced concrete.
The multi-story buildings in this
country are generally designed to
withstand a wind load of fifteen
pounds per square foot. For an
There are three earthquake zones,
the Pacific Coast area having the
shelters with an earth cover of
about eighteen inches. These were
not particularly well built, yet in
some cases they survived at a dis-
be about the same as that on rein-
American steel industrial buildings would probably fare no better
half the vertical design live load.
there
allowable working stresses. These
buildings would be proportionately
more resistant as the ratio of the
horizontal to the vertical load increased.
The effect on steel-frame buildings, such as multiple storied office and hospital structures, should
there is no direct guide from dam-
age to the small bridges in Japan.
is usually taken as dead load plus
semi-buried
on
7
a
provide for the design of structures to resist horizontal, earthquake forces varying from 2 to 16
per cent of the vertical load, which
Damage to Caves
Caves were used to a large ex-
were
_
than those in Japan, according to
expert opinion. The sawtooth roofs
designed as rigid frames would be
Tests made on typical housing
of wood-frame construction with
conventional bombs up to 500
pounds and at various distances
indicate a high degree of resistance
against blast beyond thirty feet.
While no direct interpretation of
these results can be made with regard to the blast from a large
explosion, which would have quite
different characteristics, it is believed that the radius of material
structural blast damage would not
exceed 7,500 feet.
This is slightly
less than that in Nagasaki where
the severe damage to houses ex-
from the explosion, vessels of all
types would suffer serious damage
or would be sunk.
Moderate dam-
age would be inflicted out to 4,000
feet, and minor damage would be
expected to occur within a radius
of 6,000 feet.
Because of the shock wave trans-
mitted through the air, exposed
structures, such as masts, spars,
radar antennae, etc., would be expected to suffer damage.
This
would be severe up to 3,000 or
3,500 feet from the explosion.
With the same radius, vehicles
and airplanes on the ships, and
other light structures and electronic equipment would be serious-
Iy damaged.
Boilers would be ex-
pected to suffer heavy damage up
to 2,700 feet, moderate damage to
4,000 feet and light damage to
nearly 5,000 feet. This would account for most cases of immobilization.
The damage to be expected from
an underground detonation appears to be less than from an air
burst. It has been estimated that
a bomb dropped from the air,
which penetrated to a depth of
forty to fifty feet below the sur-
face before exploding, would cause
blast damage over radii of about
one-half to two-thirds of the radii
for corresponding damage due to
an air burst.
However, the reflection of the
shock wave from rock strata, at
depths of less than 200 to 300 feet
beneath the point of detonation,
would probably result in an appreciable increase in the area of dam-
age.
If a nominal atomic bomb were
dropped in such a manner as to ex-
plode at a depth of about fifty
tended to 8,500 feet.
Air Bursts Over Water
From the data obtained in the
feet in ordinary soil, a crater of
about 800 feet in diameter and 100
feet in depth would be produced.
Bikini ‘Able’ air burst, it may
be concluded that the general nature of the damage to houses and
other buildings and installations
on shore by air burst over water
would be much the same as air
Tests indicate distributions of appreciable quantities of crater ma-
contents would be almost entirely
from the shock wave in air. From
the results observed at Bikini, it
appears that, up to about 2,500 to
3.000 feet of horizontal distance
activated by neutrons.
The major portion of the shock
from a shallow underwater explosion is propagated through the
terial to a radius of one mile down-
wind and 0.2 mile upwind.
The
material expelled from the crater
would be highly radioactive, be-
burst over land.
Destruction of ships and their
cause of the presence of trapped
fission products and of material
water.
21
The sinking range of all