Page 14 - Advanced Design Examples of Seismic Retrofit of Structures

6 Advanced Design Examples of Seismic Retrofit of Structures

1.4 BASIC TERMINOLOGY IN SEISMIC RETROFIT STANDARDS
1.4.1 Design Basis

Provisions of standards for seismic rehabilitation are mostly founded on a
performance-based design methodology that differs from seismic design proce-
dures for the design of new buildings currently specified in most building codes.
The framework in which these requirements are specified is purposefully broad
so that rehabilitation objectives can accommodate buildings of different types
that satisfy a variety of performance levels for different seismic levels.

1.4.2 Rehabilitation Objective
Building performance can be described qualitatively in terms of: the safety
afforded to building occupants during and after the event; the cost and feasibil-
ity of restoring the building to its pre-earthquake condition; the length of time
for which the building is removed from service for effective repairs; and eco-
nomic, architectural, or historic impacts on the larger community. These perfor-
mance characteristics are directly related to the extent of damage that would be
sustained by the building. In this scope, the extent of damage to a building is
categorized as a building performance level. A broad range of target building
performance levels may be selected when determining rehabilitation objectives.
Probabilistic earthquake hazard levels are frequently used in standards or their
corresponding mean return periods (the average number of years between
events of similar severity). The rehabilitation objective selected as a basis
for design will determine, to a great extent, the cost and feasibility of any reha-
bilitation project, as well as the benefit to be obtained in terms of improved
safety, reduction in property damage, and interruption of use in the event of
future earthquakes. Readers are referred to [8] for more details on the efficient
selection of rehabilitation objectives.

1.4.3 Target Building Performance Levels

A target building performance level consists of a combination of a structural
performance level and a nonstructural performance level. Table 1.1 presents
a sample of such performance levels derived from FEMA 356 [6].

1.5 REVIEW OF COMMON RETROFIT OPTIONS

There are many specific methods of intervention available to retrofit designers,
both to improve the behavior of individual building components and to improve
overall behavior [5]. A complete listing of all techniques becomes a treatise on
structural engineering because all materials and systems used in new construc-
tion can also be used in a retrofit. The selection of the specific type of element or
prefabricated hardware depends on local cost, availability, and suitability for