Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 353

- the limited ductility “L” class, which corresponds to the application of
Eurocode 8, without any additional condition except for the ductility of materials.
Actually, Eurocode 8 is deemed to confer some limited ductility that can be taken
advantage of, as the behavior coefficient is limited to 1.5 in that case. This can be
quite useful in low seismic areas when economically justified. Stresses due to wind
can be higher than those due to an earthquake, at least in the short-dimension
horizontal direction (or “gable plane”). This class is not specific for reinforced
concrete, and similar layouts have been adopted for steel frames with Eurocode 3
and for mixed structures with Eurocode 4;
- a medium ductility “M” class for which layouts specific to a seismic situation
are used to ensure ductility and dissipation without any brittle failure occurring;
- the high ductility “H” class that enables energy dissipation higher than in the
previous class.
A q behavior coefficient is associated with each ductility class, dependent on the
structure type.
9.6. Designing and dimensioning reinforced concrete structure elements
9.6.1. Regulations specific to reinforced concrete in seismic areas
Specific regulations govern the design of main and secondary structural
elements, diaphragms, construction arrangements and reinforced concrete pre-cast
elements.
As far as the calculations of the bending moment (potentially composed) and
shear loads are concerned, Eurocode 2 verification rules apply.
Reinforced concrete structures must comply with the capacity design rules given
in section 9.3.4. Local ductility should be organized to allow rotation within the
plastic hinges, when some can form.
To achieve this, several conditions specific to the structure elements involved
have to be met: concrete and steel must have improved features, the reinforcements
must have sufficient ductility (length of the plastic plateau without any reduction of
strength) and strength must be exceed their elastic limit. For concrete, this equates to
compression strength and ductility. In addition, rotational ductility should be
ensured by the use of appropriate layouts, particularly where confined concrete is
concerned, and the possibility of premature failure due to shear loading must be
minimized or completely eliminated.