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for a period range less than 3.0 second, but it must be deleted now, because of the band broadening
mentioned above. A slow declining line has been adopted instead in the new code, as shown in figure 1,
and the amplitude of the design response spectrum a is described as a function of period T as
follows
5T
s n
CD
where a max is the maximum value of the design response spectrum, T g is the characteristic period,
7 is the descending rate of the design spectrum in period range from T g to 5 T g , and depends on the
damping ratio as
0.5 + 5C
and
77, is the descending rate of the design spectrum in period range from 5T g to 6.0 second, given
as
ty =0.02 + (0.05-£)/8 (3)
and taking a value of 0.0, if the value is negative from the above equation.
77., is the damping
adjustment factor, given as
(4)
taking a value of 0.55, if the value calculated from the above equation is less than 0.55.
Provision for
a max and T g
The improvement in design spectrum provision arises mainly from the revision of the China Seismic
Zoning Map. A new national seismic zoning map of China, also the state standard GB 18306-2001,
was issued by the State General Administration for Quality Supervision and Inspection and Quarantine
at the beginning of 2001, and was put into practice in August, 2001. The zoning map consists of two
sheets, one for ground acceleration, the other for the characteristic period T g . On the acceleration map,