Ground Motions and Structures - Earthquake Engineering for Structural Design - page 295

Chapter8

GroundMotionsandStructures

8.1STRUCTURE INFLUENCEONGROUNDMOTIONS

8.1.1Building,the NewSubject intheSeismicApproach

For a long time, the realistic evaluation of the structural response of buildings during
an earthquake was considered inaccessible for practical design. Although the design
procedures already started to be proposed in the middle of the 20

th

Century, it is only
during the last decades that improved and intensified research works have revealed
how to effectively evaluate the actual response of structures.
In addition to the previous chapters, where only the complex ensemble of source,
travel path and site soil are considered, this chapter is dealing with a new subject, the
building as a whole (Fig. 8.1).
During an earthquake, seismic waves arise from sudden movements in a rupture
zone in the Earth's crust. Waves of different types and velocities travel different paths
before reaching a building's site, where the local ground is subjected to various
motions. The ground moves rapidly back and forth in all directions, usually mainly
horizontally, but also vertically. Then the foundations of the building are forced to
follow these movements. The upper part of the building remains in delay in respect to
the foundation moving, due to its mass. This causes strong vibrations of the structure

Figure 8.1 Source, waves and building (after MCEER, nd)