Introduction

Moving load problems exist in a wide variety of applications: rail mechanics; dynamics of computer tapes; floppy and hard discs; automotive and aircraft braking systems; belt drives; web winding and conveyer systems. Typical moving load problems can also be found in the vibration of tracks; bridge or ground excitations from travelling vehicles; noise and vibration from spinning computer hard discs; and even in the machining processes in manufacturing. As modern lightweight and high strength materials are very popular in engineering, it is expected that vibration and instabilities problems due to moving loads will numerous. Knowledge of the dynamic loads acting on a structure is very important for the

design, control, diagnosis and life management of a structure. Techniques for force identification have been developed independent of the direct measurement and instrumentation but requiring only the measured responses of the structure. Problems where the force initiation site is known, or both the force and its location are not known, have been studied in the last two decades. Techniques that identify the forces in motion without disturbing the normal operation process have attracted interest from many engineers and researchers. A literature review is presented below on the various methods developed in this area including the analytical methods, numerical prediction models, laboratory measurements and numerical methods of simulation. The basics of the solution algorithm of the ill-posed problem are discussed with a brief introduction to the modal condensation techniques which are most useful for the problem solution with only limited measured information compared to the total degrees-of-freedom of the structure. Particular emphasis is placed on those different analytical techniques, with different types of measurements, which are successful in the identification of the moving interaction forces of a bridge-vehicle system.