A Design Method for the Seismic Upgrade of Existing R.C. Frames by Buckling Restrained Braces

Abstract eng:
A large part of existing buildings in the world has been designed without considering seismic provisions. These buildings are generally not adequate to resist seismic force and need to be upgraded. The insertion of buckling restrained braces (BRBs) is believed a promising and innovative technique for the seismic upgrading of existing r.c. frames. These elements provides the r.c. structure with both lateral stiffness, thus reducing damage in reinforced concrete members during medium intensity seismic events, and dissipating capability, thus preventing collapse during strong seismic events. Furthermore, stiffness and strength of a BRB may be defined, practically independently, by choosing appropriate values of cross-section area, length of the yielding segment and yield stress of the steel. This can make the use of BRBs a very powerful and flexible tool for the seismic rehabilitation of a structure, if proper design tools were available. In this paper a method is proposed for the design of BRBs. It aims at obtaining a widespread distribution of the plastic deformation along the height of the building. The parameters which rule the design are determined by the analysis of the seismic response of a six-story r.c. frame, representative of structures designed to resist only gravity loads according to the Italian code of the early seventies.

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