Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 421

Advances in Seismic Design Methodologies 421

characteristics of seismic response. The non-linear static procedure, often called push-
over analysis, uses simplified non-linear techniques to estimate seismic structural
deformations. The non-linear dynamic procedure, commonly known as time-history
analysis, due to the dynamic nature of seismic excitation, is the most available method
to determine the structural behavior during an earthquake. But the cost of such analysis
is generally high, while the results correspond to a particular excitation only, which
does not offer a reliable basis for design.

9.5.3 Equivalent Static Analysis

The more simple procedure is the so-called equivalent static force analysis, sometimes
also called the simplified dynamic analysis. This method may be available when one
particular mode of vibration is predominant as compared to others and the system is
accurately modeled by a single degree of freedom system. In this case the design
spectrum method is reduced to one mode of vibration to express the dynamic behavior
of the system. Usually, the first mode shape is considered as a primary mode of
vibration, which can be simplified further into a simple line. The equivalent static
forces are computed as shown in Figure 9.23 for the fundamental period of vibration.
Then, a classical static analysis can be performed under the action of these equivalent
static forces. This method is an approximate method, which is adequate for certain
types of structures (regular buildings) and ground motions (having natural periods

Figure 9. 23 Equivalent static analysis