ABSTRACT
There is considerable concern that some masonry arch bridges in Britain may be deteriorating rapidly as a result of increasingly heavy traffic and axle loads. An accurate assessment of the structural condition of these bridges is known to be extraordinarily difficult because of the wide range of configurations and materials that have been used in their construction. There is also a wide range of ages and, indeed, some of these bridges are classified as ancient monuments. Accurate methods of structural condition assessment are required if timely and cost-effective maintenance is to be achieved. If this cannot be done with sufficient precision then, in some cases, these structures may deteriorate increasingly rapidly as a result of developing structural faults, not only in the pavements but also in the arch structure itself. However, this is not to say that they will immediately fall down. The static strength of masonry arches is generally very much higher than the applied traffic loads, as has been shown by some recent tests to destruction.1 The real
problem is the progressive wear and tear of the structure. This can take many forms and some frequently observed ones are:
(a) mortar decay and erosion leading to arch barrel deformation or cracking; (b) separation of spandrel walls, together with the outer parts of the barrel, from the rest
of the arch barrel; (c) fill deformation leading to an uneven pavement with consequent increases in dynamic
wheel loads and possible damage to services, such as gas pipes; and (d) foundation settlement.
