Challenges for the Next Generation of Seismic Codes - Earthquake Engineering for Structural Design - page 454

numerical modeling, provided that the seismic action is correctly defined. This
significant progress, which has been recently achieved, is also due to the collection
of a great amount of information concerning the features of earthquakes and due to
worldwide activity in research on the behavior of structures in seismic areas.
However, the current code design methodologies fail in introducing some
theoretical achievements in design practice, due to the following aspects (Gioncu
and Mazzolani, 2002, 2006, Gioncu, 2006):
(i) The design philosophy for earthquake loads is totally different from the

design methodology for other actions, giving to structural designers
many problems of assimilation of this unconventional design
philosophy. While for dead and live loads, wind and snow, the
structure must remain without damage after the maximum loads were
reached, in case of seismic design, the admittance of plastic
deformations during severe earthquakes implicitly anticipates the
occurrence of structural damage. The philosophy of structural seismic
design establishes the target level of safety that structures should resist
for minor quakes without damage, moderate earthquakes with
moderate structural damage and for major earthquakes, important
damage without structure collapse. So, the most relevant performance
criterion for a building structure surviving a strong earthquake is the
total cost of damage. This damage control is very difficult to be
quantified in a simple manner to be introduced as provision in a design
code. “What level of risk to public is acceptable? “ is a question very
difficult to be considered by code provisions.

(ii) The basic concepts of today's seismic codes were born almost 70 years

ago, when the knowledge about seismic actions and structural response
were rather poor. Today, the seismic design philosophy has grown
within the new fields of Engineering Seismology and Earthquake
Engineering, wherein many exciting developments are predicted in the
near future. The challenge for a proper seismic structural design is to
solve the balance between seismic demand and structure capacity.
Seismic demand corresponds to the effect of earthquake on the
structure and depends on the proper ground motions modeling.
Structural capacity is the structural ability to resist these effects
without failure. Looking to the developments in Engineering
Seismology and Earthquake Engineering, it is clear that the major
effort of researchers was directed towards the structural response
analysis. Therefore, the structural response can be predicted fairly
confidently, but these achievements remain without real effect if the
accuracy in determining the seismic actions is doubtful.

(iii) The prediction of the ground motions is still far from a satisfactory

level, due to both the complexity of seismic phenomena and the
communication lacks between seismologists and engineers. This
remark can be confirmed after each important earthquake, when new
and new in situ lessons regarding the characteristics of ground motions
are learned, instead of providing in advance the missing data from the