A History of Research and a Review of Recent Developments

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The effects of explosive loading
suggested that the blast effects were similar to those produced by 35 300 lb of
TNT detonated at a height of 147.6 ft (45 m). According to US safety standards,
brick buildings farther away than 1312 ft (400 m) would have been safe, but
the damage extended beyond this distance. It was concluded that for this type
of vapour cloud explosion damage is directly related to peak overpressure.
Gas explosions in dwelling houses can cause the outward deformation of
brick, masonry or precast wall panels. Structural loads due to a range of gas
explosions have been measured by the UK Building Research Establishment,
where pressures and wall displacement time histories were recorded during
the demolition of maisonette blocks. The results have been summarized by
Ellis and Crowhurst in two reports ([8.15] and [8.16]). Aerosol canisters
containing butane were ruptured and the contents ignited to produce internal
peak pressures similar to those in domestic gas explosions. Peak pressures in
the range 2.6 KN/m 2 to 9.0 KN/m 2 were generated, depending on the size of
the canister. Although structural damage to partitions and internal doors was
significant, there was no permanent damage to main structural walls. The
largest measured displacement of a wall panel was 0.63 mm for a 9.0 KN/m 2
explosion (750 ml canister). Typical room volumes ranged from 17.5 m 3 (smaller
bedrooms and kitchens) to 28.1 m 3 (large second-floor bedroom).
A collation of reports of gas explosion damage to domestic buildings has
been made by Moore [8.17] in which explosions are classed in terms of the
severity of damage, as moderate, severe and very severe. A moderate explosion
can destroy a relatively weak structure, such as a small brick or masonry bungalow.
The effect of blast on dwelling houses of brick was also investigated during
the Second World War by the US authorities. Experiments at full scale were
undertaken at the Aberdeen Proving Grounds of the Corps of Engineers, and
at Princeton University, and the results were summarized in the NRDC technical
report on the effects of impact and explosion published in 1946 [8.18]. One
series of tests concerned a structure, 6.5 ft square, 4 ft high, with a reinforced
concrete floor, roof and columns, enclosed by brick walls, which were bonded
to the framework along their bottom and sides but which were free at the top.
Charges consisting of 22 and 44 grams of tetryl explosive were detonated at
the centre of the enclosed space, and 0.5 and 1.0 lb charges of TNT were
exploded outside the structure, 3 ft from the centre of the brick wall.
The 44 gram charge completely blew out one wall (one course thick), whereas
the 22 gram charge caused enough cracking to reduce structural strength to
zero, without actually blowing the wall outwards. The external detonation of
0.5 and 1.0 lb charges of TNT 3 feet from the centres of already cracked brick
walls showed no appreciable additional effect. When a 0.5 lb charge was
detonated within the structure complete destruction resulted.
At larger scales (20 ft square, 12 ft high), with 12 in thick brick walls, it
was calculated that internal explosions of 1.25 lb TNT would cause serious
wall cracking, that 2.5 lb would blow out the walls without destroying the
frame, and 15 lb would cause complete destruction. 30 lb of TNT detonated