Seismic Upgrading of Existing Structures

Abstract

This chapter presents important considerations for engineers upgrading the seismic resistance of existing structures including investigation of existing structural characteristics, identification of significant deficiencies, and selection of appropriate upgrade criteria and retrofit systems. In addition to all of the tasks required in design of a new structure, successful seismic upgrade of an existing structure requires development of a thorough understanding of the existing construction, research into its limiting strength and deformation characteristics, quantification of the owner’s economic and performance objectives, and selection of an appropriate design criteria to meet these objectives, which is also acceptable to the building official. It also includes selection of retrofit systems and detailing which can be installed within the existing structure (which may have to remain open during the upgrade) at a practical cost and with minimum impact on building appearance, function and historic features. This chapter is organized into six sections. The differences between the seismic design philosophy for a new building and that for the upgrade for an existing building are discussed first followed by discussions on seismic deficiencies commonly found in buildings, the importance of establishing a rational seismic upgrade criteria, upgrade methods to mitigate common seismic deficiencies, and two example seismic upgrade projects. Since performance based design techniques are presented in a separate chapter of this handbook, we limit ourselves here to coverage of more traditional approaches to seismic rehabilitation.