Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 350

displacement, without making any increase for weaker periods (except for the target
displacement in the “push-over” method).

F
F e, u

F e

F dim

d u

d e d

d

Figure 9.20. Perfect elastic-plastic behavior

Figure 9.20 shows that value of the behavior coefficient has a limit, determined
by the ultimate displacement the structure can withstand before collapsing.
Eventually F . This global criterion is expressed on reaching ultimate

strains the building cannot exceed. A law expressing the global behavior of the
structure integrates the local behaviors linked to the ductility of the materials used. It
also depends on the degree of hyperstaticity and the type of the elements used
(beams, slabs, columns, walls, piers), as well as on their distribution in space.

q F

e , max dim

In practice, it is meant to represent the maximum value of the behavior
coefficient, assuming it is reached at the ULS. This means that, for a lower load
level, a smaller behavior coefficient will be used. If the load is low, the structure
remains elastic and the behavior coefficient is equal to 1. As mentioned in section
9.3.3.2, it is not acceptable practice to use the maximum behavior coefficient for a
seismic level weaker than the one for which the structure was designed.

The behavior coefficient also allows other less easy to master phenomena to be
incorporated: for instance, structure irregularity implies a reduction of the behavior
coefficient, i.e. an increase of the design strength of the structure, because
irregularity-linked phenomena are more difficult to control.

It should be noted that the behavior coefficient is not used when calculating
displacements or for determining the opening of joints.