Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 436

436 Earthquake Engineering for Structural Design

and duration. So, it is possible to generate an earthquake scenario in the form
of a time-history representation, different for interplate earthquakes (with
differences in pulse velocity types resulted from subduction, collision or
strike-slip), intraplate earthquakes (produced by ancient or rift faults) or
intraslab earthquakes.
Between these two ways, in the perspective of introducing the influence of
earthquake types in design practice, the use of the artificial time-history representation
seems to be very promising for structural design.
Hysteretic models for components behavior , which must include the strength and
stiffness deterioration. Results of seismic evaluation of various frames demonstrate that
the strength deterioration becomes a dominant factor, when the response of the
structure approaches the limit state of collapse. Therefore, the implementation of the
non-linear dynamic earthquake analysis is not complete without models capable of
tracking the history of beams, columns and connections damage until or at least close
to collapse, and incorporate, in an explicit manner, the effects of deterioration in the
seismic response. The main hysteretic models for steel, reinforced concrete and
plywood are presented by Ibarra et al (2005).
Time-history analysis . The method is based on the direct numerical integration of
the motion differential equations. In this aim, different algorithms can be adopted,
where the elasto-plastic deformation of the structure must be considered. The analysis
of the structure (Fig. 9.32a) may be performed by using, as base excitation, an actual or
artificially generated ground motion, in the form of acceleration time-history (Fig.
9.32b). The variation of displacements (or forces) at different levels (or points) in the
structure are presented in Figure 9.32c, also in the time-history form.
.One can see that an amplification due to resonance effects, an increasing of motion
duration and the tendency of regularization of movements result as far as the level
increases from the bottom to the top.
Incremental dynamic analysis . The time-history analysis determines the dynamic
behavior of a structure for a given level of lateral loads. By analogy, by passing from a
single static analysis to the incremental static push-over, one obtains the extension of a
single time-history analysis into an incremental one, where the seismic loading is
scaled. So, the structure is submitted to a succession of dynamique analyses under an
increased load intensity (Fig. 9.33) with the objective to obtain more realistic
information about the structural behavior under seismic actions (Pinho, 2007). This
involves successive scaling and application of each accelerogram followed by
assessment of the maximum response, up to the achievement of the structural collapse.
Incremental dynamic analysis (IDA) (Vamvatsikos and Cornell, 2002) is a
parametric analysis method which allows obtaining the capacity curve from a dynamic
analysis. This procedure offers to investigate, by scaling the induced base acceleration,
a continuous picture of the structural behavior from elastic to yield range and
eventually to collapse. The method allows tracing also the sequence of yielding and