The behavior of a lead rubber bearing
is modeled as a bilinear hysteretic element,
with an initial stiffness (Ke), yield
force (Fy) and secondary stiffness (K2
or Kd).
For response spectrum analysis the effective
stiffness (Keff), and the equivalent viscous
damping which is derived from the isolator's
EDC (Energy Dissipated per Cycle) are
required.
For nonlinear time-history analysis,
the bilinear properties of the isolator
(initial stiffness Ke, yield force Fy
and the secondary stiffness K2) are used.
The vertical stiffness of the isolators
is also required as part of the element
description. An interesting characteristic
of elastomeric isolators is that the compression
stiffness is about 100 times the tensile
stiffness. Care must be taken in modeling
the vertical stiffness to ensure the accuracy
of the analytical results.
Typical values of these parameters for
a wide range of DIS isolators are shown
in the Isolator
Properties Tables.
DIS can provide specific modeling parameters
and assist with the fine tuning of the
isolation system throughout the design
process.
