A History of Research and a Review of Recent Developments

192
The effects of explosive loading
photographs of the destruction have been released by the UK Public Record
Office and reproduced by Her Majesty’s Stationery Office. The report on the
Seine bridges [8.19] was in four parts and one of the authors was Dr Frances
Walley. Dr Walley, as a young scientist and engineer, carried out many research
projects during the Second World War in support of the Research and Experiments
Department of the UK Ministry of Home Security. Much of his outstanding
work is still relevant, and he has recently published a valuable paper on the
wartime efforts by himself and others in support of the need to understand the
fundamentals of the effect of explosive forces on structures [8.20].
The Seine bridges report makes the general point that continuous girder
bridges are very resistant to collapse by bombing, and that in many positions
the main girders of such bridges can be severed without concomitant collapse
of the entire structure. There is a usually generous allowance in design to
cover redistribution of forces and moments due to cuts under dead load
conditions only. To guarantee collapse it was usually necessary to cut two
main booms in the same bay. It was also clear from the survey that the most
vulnerable components of heavy girder bridges were the piers. Masonry arches
were found to suffer greater local damage from single hits, but the spans were
less and temporary repairs were more readily carried out. The number of hits
was very low on the Seine bridges. For every 100 bombs released in all types
of attack (high level and low level) three direct hits were scored, two on the
superstructure, one on the supports.
The study concluded that for railway girder bridges the most efficient general
purpose bombs were 2000 lb in total weight, and for road girder bridges 1000
lb bombs were more appropriate. For masonry arch bridges the effectiveness
of the bombs varied with span, from 1000 lb bombs (0 to 50 ft), to 2000 lb
(50 to 100 ft). Although there were instances of 500 lb bombs being effective
between 0 and 50 ft span, the use of 1000 lb bombs was thought to be preferable.
High-level attack with instantaneous fusing of the bombs was recommended
for girder bridges, and low-level attack with delayed fusing for masonry arches.
The Bombing Research Mission ascertained the effect of bombs of known
weight across the Seine between Paris and Rouen. Ten railway girder bridges,
nine railway arches, five road girders and three road arches were examined.
In terms of residual strength, rapid repair and speedy re-use, some of the
bridges examined provide useful information. We will look at these in turn:
(a) d’Eauplet bridge (railway) at Rouen, Figure 8.2.
The bombing history was as follows:
7 May 1944 70×1000 GP bombs No damage
25 May 1994 54×500 GP bombs No damage
25 May 1944 8×500 GP bombs No damage
27 May 1944 45×1000 GP bombs Pier 3 severely shaken
28 May 1944 46×1000 GP bombs Pier 3 hit again, causing complete
20×500 GP bombs destruction.