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    thermore, even if the ground motion values for collapse-
    prevention-level earthquakes were accurately defined using
    a seismic hazard analysis, the collapse risk of building
    structures still would not be geographically uniform throug-
    hout the nation because the hazard of a mega-earthquake
    (i.e., an earthquake more intensive than the collapse-pre-
    vention-level earthquake) [1] is different for different re-
    gions.
    Before 1997, the seismic zonation of the United States
    was mapped based on the  earthquakes with an exceedance
    probability of 10% in 50 years. Since 1997, the maximum
    considered earthquake (MCE), corresponding to an ex-
    ceedance probability of 2% in 50 years, has been defined as
    the baseline for the seismic zonation of the United States.
    Recently, some adjustments have been applied to MCE
    ground motions to achieve a uniform collapse risk of 1%
    collapse probability in 50 years [7]. The development of the
    current seismic zonation map of the United States provides
    a good model for future seismic zonation mapping of China.
    This paper first presents the basic concept of IDA-based
    collapse fragility analysis. Second, three cities with the
    same seismic fortification intensity but different seismic
    hazards are selected for analysis. The collapse risks of a
    given reinforced concrete (RC) frame structure located in
    each of the three cities are  predicted and compared. The
    result shows that though the three cities have the same
    seismic fortification intensity, the collapse risks of the same
    building in the three cities are quite different. Additional
    research is required to develop the uniform-risk-targeted
    seismic design approach proposed in this paper.
    2  Collapse fragility analysis based on IDA
    2.1  Basic process
    Collapse fragility analysis [3–5] based on IDA [6] involves
    the following four steps: (a) subjecting a structural model to
    a set of  Ntotal  earthquake ground motion records, (b) in-
    creasingly scaling each ground motion to multiple levels of intensity, (c) implementing nonlinear time-history analyses,
    and (d) obtaining the collapse probabilities versus intensity
    levels for further statistical analysis. At a certain intensity
    level, the number of ground motions that will result in
    structural collapse is referred to as  Ncollapse. The collapse
    probability at this intensity level is estimated as  Pcollapse=
    Ncollapse/Ntotal. By step-by-step scaling of the intensity level,
    the complete sequence of the building’s structural behavior
    can be investigated, from elasticity to yielding to collapse.
    Meanwhile, the serial collapse probabilities versus incre-
    mental intensity levels are obtained (see the data points
    shown in Figure 1(a)). By assuming a rational probability
    distribution (e.g., a lognormal distribution [4, 5]), the cu-
    mulative distribution function of the selected intensity
    measure (IM) corresponding to structural collapse, referred
    to as the collapse fragility curve as shown in Figure 1(a), is
    obtained by statistical methods. The collapse fragility curve
    is a rational representation of the structure’s collapse re-
    sistant capacity, and its reliability depends on the selection
    and the total number of the ground motion records adopted
    in the IDA [11]. The FEMA 695 report proposes that the
    number of ground motion records should be larger than 20
    to reflect the random nature of earthquakes [11].
     2.2  Probabilistic significance of the collapse fragility
    curve
    The collapse fragility curve represents the conditional col-
    lapse probability at given values of  IM, denoted as P  (col-
    lapse|IM) (see Figure 1(a)) [12]. For a given ground motion
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