A History of Research and a Review of Recent Developments

Civil bridges 191
externally a distance of 10 ft from the wall would not seriously damage it. It
should be noted that these early experiments were made with no venting to
reduce the degree of confinement.
Glass and light sheeting in buildings are very damage-prone under the action
of blast loads or penetrators. Unless treated on the surface by the addition of
film or mesh, glass will rapidly shatter and be transformed into high-speed
splintered fragments. Light sheeting will tear and distort if made from ductile
materials, or shatter like glass if made from brittle materials. The loading will
be not unlike that calculated for similar areas of brickwork, but the effects of
the blast will be felt over larger areas.
Damage from terrorist bombs in the commercial areas of cities can be
widespread and expensive to repair. Readers will have seen photographs of
the distortion and tearing of cladding on high rise offices and the shattering of
glass in the windows of shops and public buildings. In analysing the results of
this form of blast loading, it is usually assumed that the instantaneous pressures,
and the pressure decay, are similar to those experienced by flat areas of masonry,
brickwork or reinforced concrete.
8.2 CIVIL BRIDGES
Explosive damage to civil bridges has occurred in the past as a result of military
operations, either in an attacking mode when for tactical reasons it has been
necessary to demolish bridges by bombing, artillery shells, rockets or cruise missiles;
or in a defensive situation where the demolition of a bridge prevented the enemy
from advancing along a planned route. Defensive demolition was normally carried
out by the emplacement of cutting charges on selected bridge members.
Bridge damage can also occur from non-military disasters such as vapour
cloud explosions, tanker explosions following collisions, fuel explosions
following the crashing of aircraft, or fuel explosions following earthquakes.
Instances have been recorded of damage due to terrorist activities, mainly
relatively slight damage to decks and truss members.
One of the most informative investigations into bomb damage (from aerial
bombs) on large civil bridges was made by a UK Ministry of Home Security
team in 1944 for the British Bombing Research Mission. When the Allied armies
were fighting in Normandy after D-day heavy air attacks were made on road
and rail bridges over the River Seine to prevent supplies reaching the German
divisions. After the Allied advance over the Seine and on to the Rhine and its
tributaries in September 1944, there was a chance to investigate the levels of
damage to the Seine bridges. Many of the bridges (and the majority were rail
bridges) were damaged three times during the Second World War; firstly when
the French authorities demolished parts of bridges in 1940, secondly by the
very severe bombing in mid-1944, and thirdly by the German army during the
retreat from Normandy and Northern France in the autumn of 1944. The reports
of the team of structural experts, originally secret, are now unclassified, and air