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the stiffness of the bracing and that of the structure is assigned to be two so that the stiffness of the
bracing is k b = 8000 kN/m.
Since the non-linear behavior of the friction damper is utilized to dissipate the structural energy
induced by external excitation, both the effective stiffness and damping may be increased after
implementation of friction damper. When the maximum friction force of the damper is very low, that
is ("nuxM) -» 0, it is very easy for the damper to slide. It is equivalent to the case of bared frame
where friction damper does not exist. When the maximum friction force is very high, that is,
( w mx/ m £) —»°°, the damper does not slide. It is equivalent to the case of braced frame. If the
excitation is known a priori, the maximum friction can be designed to maximize the damping of the
friction-damped structure. Under El Centra earthquake which is normalized to 1 g, the optimal ratio
between the maximum friction and the weight of the structure is 2. After friction damper is added to
the structure, the relative displacement, relative velocity and absolute acceleration are all reduced
dramatically (Figures 2 and 3). Comparing to the bared frame, the reduction in relative displacement,
relative velocity and absolute acceleration of the friction-damped frame are 64.4% * 54.6% and 48.5%,
respectively. The hysteresis loop is in rectangular shape which is consistent with the assumption of
Coulomb friction.
CONCLUSIONS
After theoretical derivation and numerical simulation, it is verified that friction damper is an efficient
device for energy dissipation. If the characteristics of the excitation are known a priori, optimal ratio
of the maximum friction force to the weight of the structure can be designed in order to achieve the
best damping effectiveness. In this paper, an innovative and systematic numerical procedure by which
a unified motion equation can be adapted for both the non-sliding and sliding phases of the system.
ACKNOWLEGEMENT
This research was supported in part by the National Science Council. This support is greatly
appreciated.
REFERENCE
Venuti, W. J. (1976). Energy absorption of high strength bolted connections, Test Report, Structural
Steel Education Council, California, USA.
Pall, A. S., and Marsh, C. (1979). 'Energy dissipation in panelized buildings using limited slip bolted
joints', Proceedings, AICAP-CED conference, 3, Rome, Italy.
Fitzgerald, T. F., Anagnos, T., Goodson, M., and Zsutti, T. (1989). 'Slotted bolted connections in
aseismic design of concentrically braced connections', Earthquake Spectra, 5.
Roik, K., Dorka, U., and Dechent, P. (1988). 'Vibration control of structures under earthquake loading
by three stage friction grip elements', Earthquake Engineering and Structural Dynamics, 16, 501-521.