Page 11 - Advanced Design Examples of Seismic Retrofit of Structures

Introduction Chapter 1 3

characterization of a nonlinear response is mandatory for existing buildings,
most of which suffer from limited deformation capacity. Due to the nonlinear
behavior and the complex nature of lateral force resisting systems in existing
buildings, the retrofit of a building is essentially a different process compared
to the design of new buildings, in which a demand is simply estimated and a
resisting element is selected so that its capacity may overcome the predefined
imposed demand. Generally, a specific verification analysis is required to
ensure that all important structural components pass their corresponding accept-
able limits after applying a retrofit solution. In the terminology of performance-
based earthquake engineering, the evaluation process determines the perfor-
mance level of the building for the design ground motion. Similarly, after a ret-
rofit, it must be ensured that the structure meets the target performance level for
the specified seismic hazard level. A convenient way to discuss the engineering
issues of evaluation and retrofit is to break down the process into steps, as shown
in Fig. 1.1. For any given building, the sequence of highlighted steps may differ,
but generally engineers must deal with all issues listed in each of the steps.

Develop knowledge
of as-built conditions

Determine local response
characteristics

Create mathematical
model

Perform global analysis

YES
Determine acceptability Finished

NO NO

Select retrofit Classify per evaluation
procedures procedure or policy

FIG. 1.1 The engineering process of risk assessment or retrofit [6].