Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 420

420 Earthquake Engineering for Structural Design

- 3-D modeling of structure, for which the spatial structural response is considered,
for important and irregular structures.
Clearly, the inelastic time history analysis, which predicts both force and
deformation (damage) demands with sufficient reliability in many elements of the
structural system, is the desired solution. The implementation of this solution requires
the availability of a set of ground motion records (each with three components), which
account for the uncertainties and differences in severity, frequency characteristics and
duration due to rupture characteristics and distances of the various faults, potentially
causing ground motions in the considered site. It requires further the capability to
adequately model the cyclic load deformation characteristics of all important elements
of the three-dimensional soil-foundation-structure system. Moreover, it requires the
adequate knowledge of deformation capacities including the deterioration
characteristics, which define the limit state of acceptable performance (Krawinkler and
Seneviratna, 1998).
It is fair to recognize that at this time none of the afore mentioned requirements for
the desired solution have been adequately developed and that efficient tools for
implementation do not yet exist. Recognizing these limitations, the main task is to
perform an evaluation process, which must be relatively simple, but able to capture the
essential features significantly affecting the performance goal. In this context, the
accuracy of demand prediction is desirable, but it may be not essential, since neither
seismic input nor capacities are accurately known.
In this perspective, a set of structural analysis methods was developed, from the
simplest to the most complex ones. It must be kept in mind that they are not necessarily
physically realistic methods, but represent a design analysis which is thought to ensure
an adequate safety for an engineered structure. These simplified analyses call for a
series of engineering judgments, from the seismological to the structural aspects
(Studer and Koller, 1994). The differences between these methods lie in the way they
incorporate the seismic input and on the idealization of the structure response. All
methods of analysis have to comply with the current design philosophy, which requires
that the a structure must not collapse and must retain its structural integrity under rare
strong earthquakes and must also not be damaged in use under frequently moderate
earthquakes. Concerning the methods of structural analysis, they can be divided into
five distinct analytical procedures:
- Linear equivalent static analysis.
- Linear response spectrum analysis.
- Linear dynamic analysis.
- Non-linear static (push-over) analysis
- Non-linear dynamic (time-history) analysis.
The choice of the analytical method is subjected to limitations based on building
characteristics. The linear procedures maintain the traditional use of a linear stress-
strain relationship, but incorporate adjustments to overall building deformations and
material acceptance criteria to permit better consideration of the probable non-linear