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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Civil buildings 185<br />
bombs, <strong>and</strong> by 1940 there were several UK reports on the behaviour <strong>of</strong> brick<br />
wall panels.<br />
Most domestic brick walls were 9 in thick, <strong>and</strong> only a small number <strong>of</strong><br />
factory or civic buildings were constructed with 13.5 in thick walls. Christopherson<br />
[8.3] reported that the static pressure to cause collapse <strong>of</strong> an 8.5 ft square panel<br />
<strong>of</strong> 9 in brickwork was about 2.25 lb/in 2 , <strong>and</strong> that the ultimate deflection for<br />
walls enclosed in steel channels was about 5 in. For 13.5 in walls the figures<br />
were 5.3 lb/in 2 <strong>and</strong> 8 in respectively. In terms <strong>of</strong> hydrostatic impulse, it was<br />
shown that for a very wide range <strong>of</strong> incident pressures the impulse needed to<br />
destroy 9 in brickwork was 92±10 lb msec/in 2 . A typical two-storey brick house<br />
<strong>of</strong> the 1940s had free wall spans between 8 <strong>and</strong> 10 feet square, <strong>and</strong> field<br />
observations following air raids on British cities showed that damage involving<br />
the collapse <strong>of</strong> at least one external wall occurred when the hydrostatic impulse<br />
lay between 64 <strong>and</strong> 84 lb msec/in 2 . Complete demolition <strong>of</strong> more than 75% <strong>of</strong><br />
all external walls occurred at impulses between 82 <strong>and</strong> 160 lb msec/in 2 .<br />
During the Second World War it was necessary to use protective brick<br />
walls to reduce blast damage on industrial constructions, <strong>and</strong> in the early<br />
years <strong>of</strong> the war the design criterion was that collapse <strong>of</strong> a wall could be<br />
avoided if<br />
ρ 0 Mw u >0.25A 2 ,<br />
(8.1)<br />
where ρ 0 is the static yield pressure, w u is the maximum permissible displacement,<br />
M is virtual mass (=0.55×true mass), <strong>and</strong> A the positive impulse <strong>of</strong> the explosion.<br />
There is an inherent safety margin in this analysis, because it assumes that<br />
there is no reduction in impulse by diffraction, <strong>and</strong> that the brick wall is<br />
rigidly supported. In practice diffraction can reduce impulse <strong>and</strong> the wall<br />
could be free to slide as a unit, underlining the importance <strong>of</strong> ductility in<br />
defensive construction. Values <strong>of</strong> impulse needed to destroy thick panels, taken<br />
from ref. [8.3] are shown in Figure 8.1.<br />
The advent <strong>of</strong> nuclear explosions <strong>and</strong> the need to assess the behaviour <strong>of</strong><br />
civilian housing under the long duration blast associated with the detonation <strong>of</strong><br />
a nuclear bomb led to much field research in the late 1940s <strong>and</strong> early 1950s.<br />
Brick houses were built at the nuclear test sites <strong>and</strong> destroyed by the blast winds.<br />
It was generally assumed that a peak nuclear overpressure <strong>of</strong> 5 lb/in 2 would be<br />
sufficient to cause the collapse <strong>of</strong> a brick structure by implosion. For conventional<br />
weapons, with a much reduced positive phase duration, higher initial overpressures<br />
can be tolerated. It has been reported by Eytan [8.4] that observed damage to<br />
Israeli structures during the period 1968–91, where the damage was inflicted<br />
by car bombs, explosive charges, artillery shells, air bombs <strong>and</strong> missiles, showed<br />
that normal cavity brick walls would be severely damaged by 7 bars overpressure<br />
<strong>and</strong> would collapse under 12 bars.<br />
Locally damaged brick walls in buildings <strong>of</strong>ten transmit loads due to<br />
structural weight by an arching action, as indicated by Rhodes [8.5] <strong>and</strong> by<br />
Williams et al. [8.6]. These authors also note that the capacity <strong>of</strong> brickwork