S I Frames with eccentric bracings

6.1 I. I. General features of the design of frames with eccentric bracings

The geometry of frames with eccentric bracings is close to that of frames with concentric bracings; some intentional eccentricities in the layout of bars generate bending moments and shear. These structures resist horizontal forces essentially by axially loaded members, but they are designed to yield first in shear or bending in 'seismic links'. The latter are zones created by the shift of bars of the reference concentric brace away from the usual intersection with other bars (Fig. 6.15).

The analysis of frames with eccentric bracings does not require all the approximations made in the case of concentric bracings, because such frames are not designed so that diagonals will buckle under seismic conditions. Diagonals are part of the non-dissipative zones; they are capacity designed to the strength of the links, in order to remain elastic and to avoid buckling.

There are several reasons for selecting a frame with eccentric bracings for an earthquake-resistant structure:

8 eccentric bracings combine stiffness with a high q factor (between 4 and 8) 0 connections are between three bars, not four as in frames with concentric bracings - this results in less complicated connection details, which may also simplify the erection of the structure

• diagonals are parts of the structural system taking gravity loads, and are considered to provide strength and stiffness against these loads.

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