A History of Research and a Review of Recent Developments

xxviii
Introduction
cities. Very detailed reports of bomb damage to reinforced concrete and steel
building frameworks were published in Britain, and from these and other
sources enough information was gathered to produce for the first time design
guidance for engineers who needed to calculate the response and strength of
structures that were specified to be resistant to accidental or man-made local
explosions.
Another military threat about which much has been written is the nuclear
explosion. Although the threat seems less immediate these days, the major
arsenals of the world still contain nuclear bombs, and the behaviour of structures
in the shock and blast wind phases of a nuclear explosion must still be assessed
by engineers. It is the duration of the dynamic pressure, or drag loading, that
is the main difference between nuclear and high-explosive detonations. The
duration of the positive phase of the dynamic pressure from a megaton nuclear
explosion can be several seconds, whereas the duration of the air blast from a
conventional high-explosive detonation may only be a few milliseconds.
Structures most likely to be damaged by the high instantaneous pressure
associated with shock front are dwelling houses. Structures likely to be damaged
by the dragforce of the blast winds are chimneys, poles, towers, truss bridges
and steel-framed buildings with light wall cladding. There are also the hazards
of fast-flying debris and fire. The threat is so great that nuclear resistant
structures are normally buried below the ground surface.
A great deal of information about the behaviour of structures of all types
was assembled after the Second World War from the controlled nuclear bomb
tests in the Pacific and at the US test site in Nevada during the 1950s. Publications
by Professor Nathan Newmark and others on the design of structures to
withstand nuclear effects, including the problem of radiation, were important
and progressive contributions to the structural mechanics of the problem.
The American Society of Civil Engineers was particularly active in this work.
The importance of underground structures led to a surge during the 1960s in
analytical and experimental research on soil/structure interaction in a dynamic
environment, and a number of simulation facilities were built in America and
Britain. As the political problems of detonation and fall-out from field nuclear
tests increased, nuclear bomb effects had to be approximately simulated by
exploding a great weight of TNT instead. Unfortunately much of the target
response information is hedged in by a high-security classification, and the
details are not freely available.
The effect of the heat flash associated with a nuclear explosion can also
damage certain types of structure, particularly when the structure is made of
aluminium. It is possible for aluminium military equipment, such as a rapidly
built bridge, to escape damage by pressure or wind, but be subjected to
temperatures that are high enough to reduce the strength of the alloy. The
other hazard, as mentioned above, is due to initial nuclear radiation. As a rule
structures designed to protect occupants against peak overpressures of 77
KPa and above should also be checked for radiation. Radiation can be