Dynamic/earthquake analysis - Computational Analysis and Design of Bridge Structures - page 522

structures under any loading level. Nonlinear procedures can also help
demonstrate how structures really work by identifying modes of failure
and the potential for progressive collapse. Nonlinear procedures will help
engineers to understand how a structure will behave when it is subjected
to major earthquakes, assuming that the structure will respond beyond
the elastic limits, and this will resolve some of the uncertainties associated
with codes and elastic procedures. The performance approach, which was
shown in AASHTO guide specifications (2012), is considered, as shown
in Table 17.2.
Performance-based engineering, with their performance levels shown in
Figure 17.8, is set to select design structural criteria such that at specified
level ground motion, the structure will not be damaged beyond certain
limiting states.
In this section, conventional dynamic analysis (nonlinear dynamic in
Figure 17.7) and modal pushover analysis procedures (nonlinear static
in Figure 17.7) to determine seismic demands for inelastic structures are
presented.

Table 17.2 Performance approach

Performance level
Life safety

Probability of exceedance for design
earthquake ground motions Operational

Rare earthquake (MCE)
3 % in 75 years

Service
Damage

Significant disruption
Significant

Immediate
Minimal

Frequency of expected earthquake
50 % in 75 years

Service
Damage

Immediate
Minimal

Immediate
Minimal to none

IO (immediate occupancy)

LS (life safety)

P

CP (collapse prevention)

P S

P S

C

B

D E

A

Deformation or deformation ratio
Figure 17.8 Performance level of structures.