Note on Excitation of Long Structures by Ground Waves

Qualitative analysis of the antiplane vibrations of long structures shows that the dynamic response to excitation by ground waves can be described by the translation of the foundation only if η (ratio of the length of structure to the wavelength of incident waves) is less than $\sim 1/1\text{,}000\text{.}$ For $1/1\text{,}000<\eta <1/100-1/10$ antiplane response of structures can be approximated by translation and rotation of ground motion about the vertical axis (torsional excitation). For $\eta >1/100-1/10$ actual wave motion of the ground must be considered, not only for the correct representation of the dynamic response of structures, but also for proper analysis of the resulting deformation of the foundations.