Friction Pendulum System > Stiffness Parameters

Friction Pendulum System (FPS) isolator is used for dynamic time history analysis when Non-linear dampers option is selected under recalc pad. Damper has linear stiffness in static calculation and dynamic properties for time history calculation. FPS element is active for all translations degrees of freedom. Element does not consider p-delta effect of sliding surface.

Setting	Description
From/To/Step	Element series, for which the section properties are input/modified.
Element type	Friction Pendulum System (FPS): Type name of the isolator.
Aero class / EccType	Irrelevant in this context
Lin-Kx, Lin-Ky, Lin-Kz	Linear stiffness in local x, y & z direction of the isolator element. This stiffness is only used in linear and eigen analysis. The local x direction is always considered perpendicular to the plane of the isolator.
Dyn-Kx, Dyn -Ky, Dyn -Kz	Nonlinear dynamic stiffness is defined in local x, y & z direction of the isolator element and is working only in nonlinear time history calculation. The local x direction is always considered perpendicular to the plane of the isolator. The stiffness in the x direction is compression only stiffness.
Radius_y, Radius_z	Radii of the friction pendulum isolator in the local y and z directions respectively. Use of higher number or zero makes the isolator flat in respective direction.
FMin_y, FMin_z	Friction coefficients at zero velocity in local y and z directions respectively.
FMax_y, FMax_z	Friction coefficients at fast velocities in local y and z directions respectively.
FAlpha_y, FAlpha_z	Friction constants which are inversely related to velocities in local y and z directions. These are also referred to as characteristic sliding velocities. Velocity depended friction in one direction is defined as: μ = FMin – ( FMax – FMin) · exp[abs(v)· FAlpha]
A, Gamma & Beta	Dimensionless evolutionary equation parameters which control the shape of the hysteresis loop. The following constant values are recommended for these variables. Default: A = 1; Gamma = 0.5; Beta = 0.5 Note: When yielding commences the following relationship between controlling constants is suggested by Constantinou et. al. (1990) and more detail can be found in Park, Wen and Ang (1986).
Summation Load case	The FPS element relies on vertical compressive force in the system to dissipate energy via friction, which is summed from static dead load normal force and dynamic force as result of each time step. Therefore, in case of Recalc option "Accumulate stiffness" selected, the summation load case containing all previously applied permanent loads must be properly specified in the Recalc pad. In LC by LC analysis the load case must contain all permanent loads acting on the structure.