ABSTRACT
Developments in the use of computers for structural design and analysis have indicated1 an urgent need for the knowledge of material properties and the actual behaviour of asbuilt structures, which can only be provided by tests carried out on those structures. Such tests which make use of applied static loads are often difficult and expensive to carry out, whereas the application of dynamic loads, whether steady-state or transient, is relatively simple; although it has to be said that the collection and processing of the response data require skill and experience if pitfalls are to be avoided. Dynamic testing also usually operates at low input force levels, producing low amplitude vibrations, usually in the elastic range of behaviour. The dynamic force applied to the structure under test can be basically of two types: first, steady-state forces such as are produced by rotating eccentric mass exciters or hydraulic actuators; second, transient dynamic forces which are produced by wind, explosions or direct impact. Steady-state studies have been previously reported.2 This paper describes the use of transient forces, input to the structure by an instrumented hammer, to assess the dynamic properties of existing bridge structures, and it presents one case history of the use of this technique.
