Introduction to Waves in Structures

This chapter provides a brief overview of structural waves and discusses their relation to the modal response of finite structures. Different forms of waves can exist in structures. The waveform corresponds to a transverse wave where the string particle motion is perpendicular to the wave direction. Another important characteristic of waves in structures is the variation of the phase speed, with frequency. As most realistic structural systems are characterized by the ability to support transverse shear as well as having internal stiffness the focus is on longitudinal and flexural waves in thin beams. Longitudinal waves are characterized by a particle motion which is parallel to the direction of propagation. Many structures are excited by disturbances which are located off the central axis of the moment of inertia of the structure leading to wave motion which is transverse to the direction of propagation. In a relatively thin beam, for example, it is extremely difficult to excite purely longitudinal motion; the net result is a combination of both transverse and longitudinal displacements. The propagation and excitation of these are called flexural transverse or bending waves is thus very important.