The computer modeling of Pall Friction Dampers is very easy. Since the hysteretic loop of the friction dampers is perfectly rectangular, similar to perfectly elastoplastic material, the friction dampers can be modeled as fictitious plasticity element having yield force equal to slip load.
ETABS / SAP2000, v8 Nonlinear
The single diagonal tension/compression brace with friction damper (Figure A) can be modeled as a damped brace using the following link properties:
Name = PFD1
Type = Plastic1
M = Mass of damped brace
W = Weight of damped brace
Rotational inertia 1 = Rotational inertia 2 = Rotational inertia 3 = 0
Direction = U1 (nonlinear  put check mark in nonlinear box next to U1)
Ke = Effective Stiffness = AE/L (properties of brace)
Ce = Effective Damping = 0
K = Stiffness = Ke
Yield Strength = Slip load of friction damper
Post Yield Stiffness Ratio = 0.0001
Yielding exponent = 10
In this case, the brace plus friction damper (damped brace) is modeled as link
element.
A = Area of Brace, L = Length of Damper + Brace
Figure A: Single Diagonal TensionCompression Brace with Pall Friction Damper
The chevron friction damper (Figure B) can be modeled using the following link properties:
Name = PFD1
Type = Plastic1
M = Mass of damper = 0.0013 (units: kip–inch)
=0.225 (units: kNm)
W = Weight of damper = 0.5 (units: kip–inch)
=2.22 (units: kNm)
Rotational inertia 1 = Rotational inertia 2 = Rotational inertia 3 = 0
Direction = U1 (nonlinear  put check mark in nonlinear box next to U1)
Ke = Effective Stiffness = 25 x damper slip load (units: kipinch)
= 1000 x damper slip load (units: kNm)
Ce = Effective Damping = 0
K = Stiffness = Ke
Yield Strength = Slip load of friction damper
Post Yield Stiffness Ratio = 0.0001
Yielding exponent = 10
The brace is modeled as frame element. Braces are from joints A
and E and joints B and E. The beams at top are from joints C and
D and joints D and F. The friction damper is modeled as a nonlinear axial link element between joints D and E. Joint E can be, say, 0.01” lower and 6” away from joint D. Make sure that joint E is disconnected from the diaphragm otherwise the damper will not work or move.
Figure B: Chevron Brace with Pall Friction Damper
Tension Only Cross Brace with Pall Friction Damper (Figure C)
Pall Cross brace friction damper is a unique device which is suitable for long tensiononly cross bracing. When tension in one of the brace forces the damper to slip, the mechanism shortens the other brace thus preventing buckling. Therefore, in the next half cycle, the other brace is ready to force the damper to slip in tension.
The analysis require that each brace be modeled to slip (yield) in tension and slip in compression at almost zero load without buckling. Computer programs like DRAIN3DX have the capability of modeling nonlinear link element with different yield values for tension and compression.
Since ETABS and SAP2000 have only one value for yielding in tension and compression, the following equivalent approach is followed.
The hysteretic loop of each tension brace is equal to hysteretic loop of one single diagonal tensioncompression brace having half the slip load. However, the brace and the connections should be designed considering the full slip load.
Figure C: Tension Only Cross Brace with Pall Friction Damper
