67 – An Introduction to the Earthquake Response of Structures

This chapter provides an introduction to the dynamics of earthquake response of buildings and other structures. The emphasis is on linear response, not because all significant earthquake response is within the linear range—certainly major structural damage and collapse are highly important nonlinear phenomena—but because an understanding of linear response provides an important background for formulating and understanding the complex and approximate methods of analysis used to describe nonlinear behavior. In addition, because the typical intent of earthquake-resistant design is to restrict damage to levels that are not significant safety hazards, linear analysis is often applicable to earthquake response because many structures that suffer only slight to moderate damage are capable of being described using equivalent linear properties. From the viewpoint of function and safety, the amplitude of earthquake response of a structure is perhaps best measured against the capacity of the structure to resist motions of different amplitudes, first without damage, then with damage, but without serious threat to the integrity of the structure, and finally against the level of response at which collapse is imminent. The amplitudes and frequency contents of earthquake ground motions corresponding to these levels of structural response obviously differ for different structures. The earthquake response of linear multi-degree-of-freedom structures can be introduced by considering the in-plane response of the simplified three-story building shown in chapter.