A History of Research and a Review of Recent Developments

9
Response, safety and evolution
9.1 INTRODUCTION
Although the text of this book deals mainly with explosive loads and their
effects, it would be an omission if we did not consider in a general way the
analytical methods that seek to predict how structures respond to blast. We
should also consider briefly the qualities of structures that are designed to
resist known levels of explosive loading, because cases exist where the behaviour
of the structure under shock loading can change the applied transient loading
during the loading process.
Most hardened land structures are designed for military purposes, although
some thought has to be given to response in the design of grain silos, chemical
and explosive production plants, power stations and offshore structure blast
walls. Any historical review has an early start, because permanent defensive
installations have been an operational requirement since the beginning of
civilization, and we are all familiar with the great defensive ditches, earth
banks and stone walls built throughout the world in earlier ages. It is interesting
to note that the Brits, the Celts and the Saxons tended to dig their fortifications,
whereas the Romans and Chinese built walls.
As the knowledge of materials and structures grew, so the fortifications
became more sophisticated, and stone-built castles became an early example
of a hardened structure capable of protecting the inhabitants from attack for
long periods, and then becoming the springboard for offensive operations.
The design of castles, like all hardened structures, was conditioned by the
type and quantity of the hostile fire expected from the enemy, and it passed
through many stages in the Middle Ages. The single large tower, or keep, was
replaced by a fort within a series of forts; the walls were increased in height
and galleries were added for archers. The coming of gunpowder and cannon
in the fifteenth century raised many new problems, because artillery fire could
be concentrated in one spot, battering down weak masonry. The castle therefore
lost its defensive capacity and was replaced by the bastioned fortress.
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