In Nagasaki, buildings with structural steel frames, principally the
Mitsubishi Plant as far as 6,000 feet from X were severely damaged; these
buildings were typical of wartime mill construction in America and Great
Britain, except that some of the frames were somewhat less substantial.
The damage consisted of windows broken out (100%), steel sashes ripped out
or bent, corrugated metal or corrugated asbestos roofs and sidings ripped
off, roofs bent or destroyed, roof trusses collapsed, columns bent and
cracked and concrete foundations for columns rotated. Damage to buildings
with structural steel frames was more severe where the buildings received
the effect of the blast on their sides than where the blast hit the ends of
buildings, because the buildings had more stiffness (resistance to negative
moment at the top of columns) in a longitudinal direction. Many of the
lightly constructed steel frame buildings collapsed completely while some
of the heavily constructed (to carry the weight of heavy cranes and loads)
were stripped of roof and siding, but the frames were only partially
injured.

The next most seriously damaged area in Nagasaki lies outside the 2.9
square miles just described, and embraces approximately 4.2 square miles of
which 29% was built up. The damage from blast and fire was moderate here,
but in some sections (portions of main business districts) many secondary
fires started and spread rapidly, resulting in about as much over-all
destruction as in areas much closer to X.

An area of partial damage by blast and fire lies just outside the one just
described and comprises approximately 35.8 square miles. Of this area,
roughly 1/6th was built up and 1/4th was water. The extent of damage
varied from serious (severe damage to roofs and windows in the main
business section of Nagasaki, 2.5 miles from X), to minor (broken or