Ground Motions and Structures - Earthquake Engineering for Structural Design - page 349

Ground Motions and Structures 349

(a) (b)

Figure 8.46 Buckling restrained braces: (a) Restrain system; (b) Hysteretic behavior
(D'Aniello et al, 2006)

8.5.4EccentricallyBracedFrames

The eccentric braced frames (Fig. 8.47) are a hybrid lateral force-resisting system. In
fact, it can be considered as the superposition of two different framing systems: the
moment-resisting frame and the concentrically braced frame. They can combine the
main advantages of each conventional framing system and minimize their respective
disadvantages, as well. In general, eccentrically braced frames possess high elastic
stiffness, stable inelastic response under cyclic lateral loading, and excellent ductility
and energy dissipation capacity.
The key distinguishing feature of an eccentrically braced frame system is that at
least one end of each brace is connected so as to isolate a segment of beam called
“link”. In each framing scheme (Fig. 8.47), the links are identified by a bold segment.
The three arrangements here presented are usually named as split K-braced frame, D-
braced frame, and finally inverted-Y-braced frame. Some details of these links are
presented in Figure 8.48. An innovative solution for replacing the damaged links after a
moderate to strong earthquake is proposed by Stratan and Dubina, (2004) (Fig. 8. 49a)
for split K-braced frames, in order to reduce repair costs. The connection of the link to
the beam is provided by a flush end plate and high strength bolts. Bolted connection
allows the link to be fabricated by using a lower yield steel grade for assuring a good
ductility. The same dismountable solution for inverted Y-braced frames is proposed by