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