Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 329

Figure 9.2. Collapse of a building showing overall torsion
Figure 9.3. Rupture at the level of a lightened storey
A building's overall dynamic behavior is determined by the strength and
ductility of its structural elements. In fact, except for specific constructions for
which preserving a quasi-elastic behavior is desirable, large incursions into the post-
elastic field are usually included in the design (see section 9.5.2). In linear element
structures such as beams and columns, this involves formation of “plastic hinges”
that will suffer alternating rotation cycles during a seismic disturbance. These induce
steel and concrete strains far higher than those at the ultimate limit state. Roughly
speaking, with such flexible structures, we can assume that the displacements
reached during incursions into the plastic field are equal to those calculated using
the elastic hypothesis. To a first approximation, the structures are subjected to
impose displacements, which allow engineers to carry out sound design, by
evaluating the rotation likely to be caused in the plastic hinges.
To avoid strains causing compression and crushing, areas that are joined by the
plastic hinges should be confined by transverse reinforcements (stirrups). The final
strength of sections is determined by the extent to which the energy dissipation