Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 343

critical areas using the capacity design method. This leads to the inequality
expressed in the following equation:

¦¦ M J M [9.2]

c d b

in which the M c moments (respectively M b ) are the design-resistant moments of the
columns (respectively beams), and J RD is an over-capacity coefficient (Figure 9.17).

Figure 9.16. Preferable mechanism

M c1

M b2

M b1

M c2

Figure 9.17. Equilibrium of a node

Capacity design also involves classifying a structure's failure modes to ensure
that brittle failure modes cannot appear before ductile modes. This ensures a planned
dissipative operation, and avoids the existence of a “cliff” effect, i.e. a sudden drop
in structure strength if the aggression level is exceeded. For reinforced concrete,
shear load behavior is acknowledged to be brittle whereas bending moment behavior
is ductile, providing minimum construction layouts are respected. To prevent a beam