# 4.2.6.5. Triple Friction Pendulum Bearing Element¶

This command is used to construct a Triple Friction Pendulum Bearing element object, which is defined by two nodes. The element can have zero length or the appropriate bearing height. The bearing has unidirectional (2D) or coupled (3D) friction properties (with post-yield stiffening due to the concave sliding surface) for the shear deformations, and force-deformation behaviors defined by UniaxialMaterials in the remaining two (2D) or four (3D) directions. To capture the uplift behavior of the bearing, the user-specified UniaxialMaterial in the axial direction is modified for no-tension behavior. P-Delta moments are entirely transferred to the concave sliding surface (iNode). It is important to note that rotations of the concave sliding surface (rotations at the iNode) affect the shear behavior of the bearing. If the element has non-zero length, the local x-axis is determined from the nodal geometry unless the optional x-axis vector is specified in which case the nodal geometry is ignored and the user-defined orientation is utilized.

element('TFP', eleTag, *eleNodes, R1, R2, R3, R4, Db1, Db2, Db3, Db4, d1, d2, d3, d4, mu1, mu2, mu3, mu4, h1, h2, h3, h4, H0, colLoad, <K>)
 eleTag (int) unique element object tag eleNodes (list (int)) a list of two element nodes R1 (float) Radius of inner bottom sliding surface R2 (float) Radius of inner top sliding surface R3 (float) Radius of outer bottom sliding surface R4 (float) Radius of outer top sliding surface Db1 (float) Diameter of inner bottom sliding surface Db2 (float) Diameter of inner top sliding surface Db3 (float) Diameter of outer bottom sliding surface Db4 (float) Diameter of outer top sliding surface d1 (float) diameter of inner slider d2 (float) diameter of inner slider d3 (float) diameter of outer bottom slider d4 (float) diameter of outer top slider mu1 (float) friction coefficient of inner bottom sliding surface mu2 (float) friction coefficient of inner top sliding surface mu3 (float) friction coefficient of outer bottom sliding surface mu4 (float) friction coefficient of outer top sliding surface h1 (float) height from inner bottom sliding surface to center of bearing h2 (float) height from inner top sliding surface to center of bearing h3 (float) height from outer bottom sliding surface to center of bearing h4 (float) height from inner top sliding surface to center of bearing H0 (float) total height of bearing colLoad (float) initial axial load on bearing (only used for first time step then load come from model) K (float) optional, stiffness of spring in vertical dirn (dof 2 if ndm= 2, dof 3 if ndm = 3) (default=1.0e15)