ABSTRACT
This chapter serves as an introduction to the field of random vibrations, which in recent years has found extensive applications in structural dynamics, machine vibrations, earthquake engineering, as well as in non-destructive testing and identification. Essentially, it is an extension of Chapter 2, which focused on deterministic structural dynamics. We note that the concepts of random variables and random (or stochastic) processes, the latter being functions of both space and time in their most general form, appear in most of the intervening chapters. For instance, wind, water wave and earthquake-induced ground motions are loadings of random nature. Specifically, the former two types of loads can be viewed as comprising a rapidly fluctuating part superimposed on a slowly varying mean value. They can be classified as stationary random loads in the sense that there is a certain periodicity (and hence some predictability) in the fluctuating part. Earthquake loads are fully random and classified as non-stationary, a term that will be explained later on. Finally, there is some mild stochasticity inherent in traffic induced loads, simply because the movement of vehicles cannot be fully controlled.
