Chapter 3: Seismic performance objectives and ductile design

Having characterised the seismic hazard at a site, as discussed in Chapter 2, the engineer (in collaboration with other stakeholders, such as the client and other members of the design team) should identify how the building is intended to behave in an earthquake. As will become apparent later in this chapter, a very important component of good seismic performance is for a building to be able to deform inelastically without collapse – that is, it must be ductile.

This chapter covers the following topics.

As discussed in Chapter 2, seismic hazard is defined probabilistically, and there are thus many possible definitions of a ‘design earthquake’ (or, more accurately, a ‘design earthquake ground motion’) for a given site. It is common even among earthquake engineers to loosely speak of a target building performance (e.g. ‘life safety’) in ‘an earthquake’, even if ‘an earthquake’ could cover several orders of magnitude of ground acceleration, depending on the return period adopted. See, for example, the hazard curve in Figure 2.9.