No matter how sophisticated, modern analytical techniques cannot replace field testing for understanding how a structure will respond under load.
As an example, parapets, sidewalks, and asphalt overlays can make a bridge much stiffer than originally designed. Or, a navigation lock gate may be distributing load much more efficiently than anticipated.
By installing strain and deflection sensors on primary structural members and recording responses while a load is applied, a clear picture can be developed of how that load is distributed.
Depending on the project, it may be enough to know that some members are being loaded and what stress levels are being reached. Other projects require a more sophisticated comparison between the field data and finite element models.