A History of Research and a Review of Recent Developments

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