A History of Research and a Review of Recent Developments

Table 4.1
Loading/time relationships 75
the faces. Drag coefficients for bodies in the subsonic flow range have been
given by Hoerner [4.3] who lists the values shown in Table 4.1 for C d for some
simple shapes (see also Baker et al. [4.4]).
Values of C d for many other shapes, including framed structures such as
masts and towers are given in books on the effect of wind on structures.
Glasstone and Dolan [4.5] gave procedures for deriving air blast loading
as a function of time for partially open box structures, framed structures and
cylindrical and arched structures, in addition to the simple box structure
considered above. They define a partially open rectangular box structure as
one in which the front and back walls have about 30% by area of openings or
windows, and have no interior partitions that might influence blast wave
behaviour. The average loading on the front face is influenced by the fact that
the value of t c is now 3s 1 /ū, where s 1 is the average distance from the centre of
a front face wall section to an edge of wall at an opening. The internal pressure
begins to rise at zero time because the blast wave enters the openings, eventually
reaching the blast wave overpressure. The dynamic pressures are assumed to
be negligible (i.e q=0) on the interior. The average loading on the sides and
top are similar to those for a closed box, but the inside pressures take a time of
2L/ū to reach the blast wave value. For much of the decay period the internal
pressure is greater than the external pressure.
The outside pressures on the back face are similar to those for a closed
structure, except that s is replaced by s 1 in the analysis. The inside pressure
reaches a similar value to that of the blast pressure, instantaneously, at a time
L/ū, and then decays. The dynamic pressure is reckoned to be negligible.
When a blast wave meets a cylindrical structure there is a very complex
interaction with the curved surface, but the loading increases from zero to a
maximum when the blast front has traversed one radius; this occurs at a time
D/2ū (where D is the cylinder diameter). It is sometimes assumed that the