Performance-based Seismic Design Of Ebf Using Target Drift And Yield Mechanism As Performance Criteria







1.1 General


Introduction

While steel moment frames can exhibit stable inelastic and ductile behavior under cyclic

seismic excitation, the concentrically braced frames usually possess greater lateral stiffness

which can limit the damage due to drift. However, moment frames are relatively flexible and

their design is usually governed by the drift limitations in order to control the damage. On the

other hand, the ductility and energy dissipation capacity of concentrically braced frames can

significantly deteriorate if braces buckle under seismic loading. Eccentrically braced frames

(EBFs) successfully combine the advantages of the moment frames and concentrically braced

frames, namely high ductility and lateral stiffness, while eliminating the shortcomings of those

frames by limiting the inelastic activity to ductile shear links and keeping braces essentially

elastic without buckling, thus maintaining high lateral stiffness during earthquake events.



EBFs are characterized by an isolated segment of beam, which is referred to as link. The

diagonal brace, at least at one end, is connected to the end of the link rather than the

beam-column joint. All inelastic activity is intended to be confined to the properly detailed links.

Links act as structural fuses which can dissipate seismic input energy without degradation of

strength and stiffness, thereby limiting the forces transferred to the adjacent columns, braces, and

beam segments. Typical EBF configurations are illustrated in Figure 1.1; in which the link length

e of each type in EBF is highlighted.


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