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levels of peak ground acceleration.
7 SEISMIC RELIABILITY ANALYSIS
The structural seismic reliability analysis is usually to determine the limit state probability PF with
respect to a particular limit state during the structural service life. It can be expressed as:
The structural reliability index with respect to a particular limit state is.
1=6
where, k, is the occurrence rate of earthquake with intensity I, during the structural service life. For a
given earthquake risk curve FI (I,), it can be written as:
P t (Ii) is the conditional limit state probability with respect to a particular limit state for a given
intensity I,, i.e., the structural vulnerability with respect to a particular limit state given above.
The peak ground accelerations with respect to various intensities are taken as 0.05g> 0.10g^ 0.20gN
0.40g and O.SOg for intensity VI, VI, VI, IX, and X, respectively.
The analytical multistory dwelling brick buildings are assumed to be located in Tianjing, Beijing and
Xichang. Their basic intensities are VI, VI, and K, respectively, and their earthquake risk curves may
refer to Ref. [10].
Table4 lists the seismic reliability indexes of four multistory brick buildings with and without isolation
located in region of intensity VI (Tianjing), VIII (Beijing) and EX (Xichang) for various limit states
and their ratios. From this table, we can see that the ratios of the seismic reliability indexes of the brick
buildings with and without isolation for various limit states are more and more large from low intensity
region to high intensity region. This illustrates that the isolated brick buildings built in higher intensity
region have better seismic performance than in lower intensity region. The seismic reliability indexes
of a six-story brick building without isolation designed for intensity VI in region of intensity VI and
a seven-story brick building without isolation designed for intensity VI in region of intensity VI for
various limit states are slightly smaller than the seismic reliability indexes of the corresponding
isolated brick buildings designed for intensity VI in region of intensity K and designed for intensity
W in region of intensity VI, respectively. Thus, compared with the brick buildings without isolation,
the isolated brick buildings can be designed with 1 intensity lower than the basic intensity, and the
story number of the isolated brick building can be broken through the limit of the code, such as a
six-story isolated brick building may be designed in region of intensity DC and a seven-story isolated
brick building in region of intensity VI. As seen in Table 1, the plane and elevation of the seven-story
brick building designed for intensity VU are the same as those of the eight-story brick building
designed for intensity VI. The seismic reliability indexes of the seven-story brick building without
isolation designed for intensity VI in region of intensity VI for various limit states are far smaller
than those of the eight-story isolated brick building designed for intensity VI in region of intensity Vfl.
Thus, compared with the brick buildings without isolation, it is no problem that the isolated brick
buildings can be designed with 1 intensity lower than the basic intensity and increasing 1 story, and it
can assure that the isolated brick buildings designed in this way have higher seismic safety.