Being among the most flexible of civil engineering structures, long span bridges deform
both dynamically and quasi-statically under a range of operational conditions including wind, traffic and
thermal loads, in varying patterns, with different timescales and at different amplitudes.
While external loads and internal forces can only rarely be measured, there are well developed and emerging
technologies for measuring deformation. It is well known that some of these technologies can be used to
validate or improve numerical simulations, which can then be used to estimate the external loads and internal
forces.
Changes in response patterns and relationships can also be used directly as a diagnostic tool, signaling unusual
loading or structural changes, but excessive deformations themselves are a concern in terms of serviceability
and allowable operational limits (e.g. of vibration, and bearing movement).
This paper discusses the challenges of deformation measurement and applications in structural identification,
performance diagnosis and load estimation, including observations of response to the most extreme
loads.