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