Challenges for the Next Generation of Seismic Codes - Earthquake Engineering for Structural Design - page 493

10.5.4 Problems of Structural Response Control
An effective design of structures subjected to seismic loads requires the use of
plastic analysis where the ductility plays an important role. The structural response
control depends on the ductility requirements, in function of the earthquake type
and the available ductility of the individual members. The ductilitychecking should
be quantified at the same level as in case of stiffness and strength (Gioncu and
Mazzolani, 2002). The required ductility (global ductility) depends on the source
and it is presented in the previous section for the interplate earthquakes. The main
problems arise for evaluating the available ductility (local ductility), which must be
determined in function of the main characteristics of ground motions. Due to the
near-source effects characterized by high pulse velocities, the available ductility
evaluation must consider the influence of strain-rate (Gioncu, 2000, Gioncu and
Mazzolani, 2002)), which can shift the ductile plastic member response into brittle
fracture (Fig. 10.17a), due to the increasing of the yield stress. At the same time,
due to the strong pulse seismic loading and to the reduced number of pulses, the
common ductile cyclic behavior is replaced by brittle fracture after the reduced
number of cycles, due to the accumulation of large plastic deformations
(Fig.10.17b) (Mateescu and Gioncu, 2000, Gioncu et al, 2000). The difference
between the subduction (thrust) and strike-slip must be considered, because the
strike-slip earthquakes are the most damaging events due to high velocities and
large ground motions producing important plastic deformations.
Figure 10.17 Fracture due to pulse with high velocity: (a) Fracture due to strain-
rate; (b) Fracture due to accumulation of large plastic deformations
(Gioncu et al, 2000)