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provisions have been improved, and are summarized and discussed in detail in this paper. There are
still some new methods and suggestions that have not been included in the revision, since they had not
been validated adequately at that time. As the end of a revision could be considered as also the
beginning of the next, those methods and suggestions need to be considered further. Some other
seismic design codes, for example, the Code for seismic design of highway engineering (JTJ004-89)
and the Design code for anti seismic special structures (GB 50191-93), are ongoing or going to be
revised in China. Therefore, it is necessary to probe into new improvement(s) as past of an overview of
the state of the art and future trends in seismic design codes.
THE IMPROVEMENTS IN EARTHQUAKE ACTION PROVISION IN GB 50011-2001
In the revision of the code for seismic design of buildings of China, many new methods and techniques
have been adopted, and quite large improvements achieved. For earthquake action provision, there are
two main improvements.
Period band of design spectrum extended
With the development of construction and urbanization, buildings are getting larger and higher, and the
fundamental natural periods of buildings are getting much longer than the 3.0 second that is the longest
period of the design response spectrum (so called seismic effect coefficient) in the former edition of
code for seismic design of buildings GBJ11-89. The long period of the design response spectrum band
must be extended to meet the demand of construction. Of course, this broadening should be based on
the reliability of the data at long period range. Since many strong ground motion records have been
observed by analog accelerographs, the data reliability firstly depends on the period band of the
instruments. Some correction techniques have been adopted to broaden the instrument
amplitude-frequency feature, originally from O.SHz to 25Hz. The Ormsby digital filter with low cut-off
frequency 0.15Hz could broaden the frequency band to 0.15Hz, i.e. the longest period is 6.6 second.
Furthermore, another correction has been made to remove the noise in the digitizing process, which
consists mainly of long period components. The long cut-off period of the filter was taken as 26cm/v,
where v is the running speed of the record paper in cm/'s. Since the paper speed was generally 4.8 cm/s,
the longest period must be
5.4 second. Therefore, the
long period design spectrum
band in the new edition of the
code is extended from 3.0
second to 6.0 second.
o.
The low limit of the long
period design spectrum in
GBJ11-89, was acceptable
Figure l ^e design spectrum in code GB50011-2001