Civil Engineering Reference
In-Depth Information
2008). The results are often presented in the form of fragility curves. The
IDA procedure provides valuable information regarding the probabilistic
distribution of damage at different seismic intensity levels, which can be
used for the development of fragility curves and seismic risk assessment of
structures. However, available research on the application of IDA for the
seismic risk assessment of bridges is limited. In a study by Mander
et al.
(2007), IDA was used for the fi nancial seismic risk assessment of bridges.
However, studies on bridges have not considered the important effects of
record selection and spectral shapes on the IDA predictions. In addition,
peak ground acceleration (PGA) has been used in earlier studies as an
intensity measure (IM). The use of PGA as an IM and scaling the ground
motion records in IDA may result in biased predictions of the spectral
shape effects and the structural responses (Vamvatsikos and Cornell, 2002).
More research on the use of IDA for the risk assessment of bridges is
needed.
This chapter focuses on IDA for seismic performance evaluation and
risk assessment of bridges. IDA involves numerous inelastic time history
analyses performed using a set of ground motion records, each scaled up
or down (Vamvatsikos and Cornell, 2002). The IDA procedure has been
adopted by some guidelines including the ATC-63 provisions (ATC-63,
2008) to determine the seismic performance, collapse capacity and fragility
of buildings.
IDA provides a thorough evaluation of the seismic responses (seismic
demands) for a wide range of seismic intensity levels corresponding to dif-
ferent damage states from yielding up to collapse.
In addition, IDA provides information regarding possible structural
responses due to different ground motion records, including estimates of
the median as well as the variability of the seismic responses, required for
probabilistic seismic performance assessment of structures and seismic risk
analysis (e.g., development of fragility curves and prediction of the annual
rate of collapse). In this chapter the main concepts of IDA are briefl y dis-
cussed and the general modelling requirements for IDA are explained. The
record selection is an important issue which can signifi cantly affect the IDA
predictions. The effects of different record selection methods and including
different earthquake types on the IDA results are presented. The concepts
of conditional mean spectrum (CMS) are explained and its application to
the record selection for IDA is demonstrated. Three different CMS curves
are developed for a site such as Vancouver where the occurrence of three
different earthquake types is possible. The concept of using fragility curves
is discussed and the use of IDA to develop the fragility curves and to predict
the probability of exceeding different damage states is explained. The appli-
cation of IDA for the seismic risk assessment of a continuous 4-span bridge
is presented as an example.
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