Challenges for the Next Generation of Seismic Codes - Earthquake Engineering for Structural Design - page 462

earthquakes. The central feature of the revised seismic design code was the
introduction of a two-phase earthquake design (Kuramoto, 2006):
(i) The first phase earthquake design targeting the safety and serviceability
of buildings during low and medium level earthquake activity.
(ii) Second phase earthquake design was added to provide safety against
severe earthquake motions.
Seismic provisions in the building code were significantly revised after the 1995
Kobe earthquake, which caused many fatalities and severe damage or collapse of
buildings. Many lessons among scientists and engineers were learnt. The
recognized need for a new generation seismic design led to the development of
performance-based engineering for serviceability, reparability and life safety. The
new 1998 Japanese regulations, elaborated by the Architectural Institute of Japan,
were introduced in the revision of the Building Standard Law. The most significant
revision towards the application of new structural elements and systems, with
structural design performance-based requirements, was given in the 2000 Building
Standard Law, Enforcement Order. The new code provisions encourage structural
engineers to develop and apply new construction technology (Midorikawa et al,
2003).
Main code specifications. Two performance objectives were defined for the
structural design under earthquake forces (Otani, 2004):
- Damage limitation: protection of structural damage under frequent earthquake
events, corresponding to a return period of approximately 50 years.
- Life safety: protection of occupants' life under extraordinary earthquake
events, corresponding to a return period of approximately 500 years.
In addition, structural specifications were prescribed for the method of
structural calculation, the quality control of construction and materials, the
durability of buildings and the performance of non-structural elements.
The intensity of design earthquake motions is established for two levels:
- For rare earthquake events (Level 1).
- For extremely rare earthquake events (Level 2), which correspond to five
times that of level 1.
The intensity can be determined on the base of the recorded accelerations near
the construction or of the generated artificial earthquake ground motions,
compatible with the response acceleration spectrum. In case of generated ground
motions, more than two accelerograms must be used. The duration of the
artificially generated ground motions must be longer than 60 sec to excite long-
period structure. In order to consider the effects of surface geology, the local
horizontally layered deposits must be considered.
The performance requirement of building under Level 1 ground motions is that
no damage is produced in structural members. Static linear elastic analysis of
structures must be carried out for this level. The performance requirement of
building under Level 2 ground motions is to not collapse, until a maximum
interstory drift of 1/100. If this value is exceeded, special arguments must
demonstrate that the cladding walls are capable of undergoing the corresponding
deformation without failure. The new procedures allow the prediction of the
maximum response against earthquake of structural members, non-structural