Bracing
systems can be broadly categorised in to concentrically braced frames (CBF),
eccentrically braced frames (EBF) and knee-brace frames (KBF) (Sarno & Alnashai, 2009). Concentric
bracing is characterised by the fact that it is connected concentrically to the
beam-column joints; it includes diagonal bracing, X-bracing chevron bracing and
V-bracing patterns (Nassani, et al., 2017). Eccentric
braced frames were introduced later on in 1978, and their design combined the
stiffness of CBFs with safe energy dissipation characteristics by connecting
the bracing members eccentrically from the beam-column joints on the beams. This
latter ability was given for the purpose of avoiding collapse in case of
extreme seismic events through the use of shear links connecting bracing to
beams that would absorb the seismic energy (Roeder &
Popov, 1978).
However, in case of an extreme earthquake, replacing these damaged shear links
would be impractical and expensive. Hence, the knee braced frame was introduced
in 1986 which allowed absorption of energy by the knee members of the bracing
system unit through flexural yielding (Ochoa, 1986). Many
researchers have worked on producing energy dissipating devices that are
implemented in the bracing connections of knee braced frames in order to
improve the system (examples in Balendra 2001). Slotted
bolt connections were introduced by Grigorian
& Popov (1994) as an energy
dissipating mechanism that was easier to implement because it required little
modification to existing construction practice, and was less expensive in that
it did not require the use of expensive materials and technologies. Balendra,
et al. (Balendra, et al., 2001) was successful in demonstrating combined slotted bolt
connections with knee-braced framing pattern that allowed increased energy
dissipation capacity under large wind and earthquake load, resulting in
economic gains from the reduced strength needed to meet serviceability