Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 354

Whilst not included to date, some layouts involving novel anchoring and
reinforcement coverings will be included in future versions of Eurocode 2.
9.6.2. Main types of reinforced concrete bracing
From the point of view of stiffness, ductility and strength, the seismic behavior
of a construction is a function of the bracing type chosen. Besides the choice of a
material, bracing depends on the geometry of each constituting element, the
horizontal and the vertical layouts of its constituents, and their interactions.
For vertical elements, two types of reinforced concrete units can be used:
columns or walls. Characterization of these elements is not definite: passing from
one to the other is continuous. Geometrical non-linearity (see section 9.6.4.1) can
play an important part in the dynamic behavior of walls because sections have an
elongated shape. It is customary to treat an element as a wall if its section is equal to
four times its thickness.
Some construction types have isolated walls as bracings, and these can
potentially behave as vertical beams with one hinge at the base. Such walls can also
be connected to different floors in a construction because lintels dissipate energy by
creating plastic hinges at their ends, subjecting walls to strains. Coupled walls can
be designed to dissipate a lot of energy into lintels, and these would have a high
behavior coefficient.
Quite frequently, walls are not separated: coffers, for example, have partitions in
both directions, very high strengths, low ductility and very good behavior with
regard to torsion if distributed on the periphery of the construction. Opening rows in
the walls can delimit the ability of lintels and piers to dissipate energy.
Another type of commonly found construction combines cores (walls that can
contain stairwells or lift shafts) and load-bearing columns considered to act as
secondary structures. If the construction has only one center core, torsion can be
high.
In the case of columns used for bracing, good overall behavior can be achieved
by ensuring continuity of moments in horizontal planes, which involves placing
beams that will form frames with the columns. The continuous beam-column sets
form frames that constitute the primary structure. Frames take advantage of a
behavior coefficient that is high, as is the degree of hyperstaticity. As section 9.3.4
explained, plastic hinges have to be placed inside the beams without ignoring the
capacity design criteria.