Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 392

392 Earthquake Engineering for Structural Design

- Life safe . Significant structural and non-structural damage occurred. The lateral
strength has still a margin against collapse. Non-structural components are secure,
but cannot operate. The building may not be safe for occupancy until repaired. The
risk of life threatening injury during the earthquake is low. The service interruption
is less than 3 months.
- Near collapse. Substantial damage occurred. The building has lost most of its
original stiffness and strength, having a very little margin against collapse. Non-
structural components may become dislodged and present a falling hazard. In case
the experts decide that the building can be repaired, the service interruption is
longer than 3 months. But in many cases the repair is not practical.
The proposed levels of damage for structure and non-structural elements
corresponding to these standard behavior states are shown in Figure 9.1. These states
represent (Gioncu and Mazzolani, 2002):
- No damage for both structural and non-structural elements for fully operational .
- No damage in structural elements, minor damage in non-structural elements for
functional.
- Repairable damage of structural elements, important damage of non-structural
elements for life safe.
- Not-repairable damage of structural elements, complete failure of non-structural
elements for nearcollapse.
The relation between the four limit states and the four probabilities of earthquake
occurrence is presented in Figure 9.2, as a performance objective matrix. The basic
objectives of the earthquake design are illustrated in this matrix as the diagonal line
which represents the minimum objectives required by the codes. The unacceptable
performances are located under these minimum objectives. At the same time, there are
enhanced objectives, if the owner consents to a supplementary payment for providing
better performance or lower risk than the one corresponding to minimum objectives.

9.3DEVELOPMENTOFMULTI-LEVELBASESEISMICDESIGN

9.3.1DifferentMulti-LevelApproaches

Performance-based seismic design is a desirable concept, whose implementation has a
long way to go. It appears to promise engineered structures, whose performance can be
quantified and conforms to the owner's desires. But this methodology will be a lost
cause, if rigorously held to this promise, as it is well known that it is not possible to
predict all important seismic demands and capacities with perfect confidence
(Krawinkler, 1999). Unfortunately, while the above parameters are quite meaningful to
the owners and users and, therefore, can serve as a basis for selecting among the given
building performance alternatives, they are not particularly useful as a basis for design.