The residual life of battle damaged bridges

The British army has a long history in the design and construction of military bridging, its latest bridges being made of large welded sections pinned together to form trackways. To utilise the strength of these bridges, there needs to be rapid assessment of the damage and then simple rules which can be applied to the assessment to indicate the load class of the damaged bridge along with the number of crossings which military vehicles can make. DERA are researching this problem in three ways Ballistic damage is most likely to occur from a near miss of a: fragmentation shell. DERA tests show this gives extensive damage which is widely spread over the sides of the panels. Such tests have been carried out on steel and aluminium alloy panels, and the damage has been carefully catalogued. Following the tests, single trackways of the bridge are built under a fatigue rig. Where they are tested under cyclic loading until the bridge fails. Computer simulation takes published data from typical shells and calculates the amount of damage which would occur in key areas. Using fracture mechanics and residual area methods applied to all the areas of damage, the lowest capacity and life of the bridge is determined. Further work is being carried out at research establishments to use the latest theories of fracture mechanics to give more realistic answers to the life of damaged units compared with the life found in full size fatigue tests. This should lead to much better assessments of the residual life of battle damaged bridges.