Response Evaluation - Fundamentals of Earthquake Engineering - page 186

P ERFORMANCE L EVELS

I NPUT

L OADS

S TATIC

S TRUCTURE

M ODEL M ETHOD

D YNAMIC

S OIL

O UTPUT

A CTIONS D EFORMATIONS

Figure 4.1 Conceptual framework for seismic analysis of structures

• Performance levels;
• Output for assessment.

The above components are discussed in subsequent sections, while noting that soil and foundation
models are beyond the scope of this topic. For the latter features, the reader may refer to the literature,
(e.g. Wolf, 1994) for fundamentals, and to numerous applications (e.g. Monti et al ., 1996 ; Stewart
et al ., 1999 ; Mylonakis et al ., 2001; Zhang and Makris, 2002 ; Sextos et al ., 2003a ; Kwon and Elnashai,
2006; Elnashai and Kwon, 2007). As mentioned above, the topics discussed in this chapter are illustrated
by an example application consisting of a three-storey irregular RC frame shown in Figure 4.2 . This
structure was comprehensively assessed within the European network on Seismic Performance Assess-
ment and Rehabilitation (SPEAR). It features irregularities both in plan and elevation. It has heavily
imbalanced stiffness in two orthogonal directions ( x and y in Figure 4.2) as well as large eccentricity
in plan and irregularity in elevation. The RC frame was designed according to modern design codes
and with no seismic design provisions. It was constructed from weak concrete and smooth bars. Further
details are given in Negro et al . (2004) and Jeong and Elnashai (2005) .

4.3 Ground Motion and Load Modelling
Modelling of input quantities, such as ground motions and gravity loads, is a critical step in the earth-
quake response analysis of structures. Approaches used to model ground motions in structural assess-
ment are visually summarized in Figure 3.1 and the various input motion forms are described in detail
in Chapter 3. To perform dynamic analysis either response spectra or time histories of earthquake
ground motion may be employed. For equivalent static analysis, as depicted in seismic codes, design
spectra are utilized to estimate lateral forces as discussed in Section 4.6.2.1. Spectral representations
are also used for advanced inelastic static analyses, e.g. adaptive pushover analysis presented in Section
4.6.2.2 . Table 4.1 summarizes commonly used methods of analysis alongside the appropriate input
representations and range of structural applications.
A number of time histories are specifi ed in seismic design standards for dynamic analysis, usually
three to seven records in each principal direction of structural response (e.g. Bazzurro and Cornell,
1994 ; Dymiotis et al ., 1999 ). For long -span structures, such as major bridges, it may be necessary to
employ asynchronous earthquake ground motions at the base supports to account for the spatial and
temporal variability of the input (e.g. Burdette and Elnashai, 2008; Burdette et al ., 2008 ). Asynchronous