I I

Eurocode 8 Preliminary SDOF Analysis of Seismic Isolation

Description:
Preliminary analysis of seismic isolation system with the equivalent linear single-degree-of-freedom (SDOF) method. Applicable for seismic isolation system with FPS, LRB, HDRB isolators and viscous dampers.
According to:
EN 1998-1:2004 Section 10.9.2, EN 1998-2:2005+A2:2011 Section 7.5.4
All Calculations
Input
g
In accordance with EN1998-1 §3.2.1(2), 3.2.1(3) and the National Annex
s
In accordance with EN1998-1 §3.2.2.2(2)P and the National Annex
s
In accordance with EN1998-1 §3.2.2.2(2)P and the National Annex. It is noted that for seismic isolation systems with long periods the displacement demands are directly proportional to TD. For bridges a larger value of TD = 2.5 s is recommended in EN1998-2 §7.4.1(1)P
kN
Typically the weight corresponding to the mass of the superstructure above the isolation interface that oscillates practically as a rigid body. For bridges it corresponds to the weight of the deck including the effect of quasi-permanent masses due to variable traffic actions, in accordance with EN1998-2 §4.1.2. The mass of the superstructure is assumed as m = Wd / g and the force of the sliding elements is assumed proportional to Wd
kN
Corresponds to the total effect of all hysteretic devices
kN/m
Corresponds to the total effect of all hysteretic devices and spring devices
m
Representative value for the total isolation system so that the dissipated energy (area of hysteretic loops) is equivalent
kN
Corresponds to the total effect of all preloaded spring devices
Corresponds to the total effect of all friction devices
m
Corresponds to the equivalent value for all friction devices so that the corresponding post yield stiffness is Kp=W/R. For R=0 the effect of the radius of curvature is ignored i.e. it is assumed that R=∞
kN⋅(s/m)αb
Corresponds to the total effect of all viscous devices
For linear viscous elements where force is proportional to velocity αb = 1. For nonlinear viscous elements αb < 1
kN/m
Corresponds to the total representative stiffness of the substructure below the seismic isolation system, e.g. the pier stiffness for an isolated bridge. For Ks=0 the effect of substructure stiffness is ignored i.e. it is assumed that Ks=∞