The influence of the vertical inertia forces on the behavior of friction pendulum bearings (FPB)

A procedure for deriving the complete equations of motion to compute an isolator’s displacement due to strong ground motion is applied to structures isolated with friction pendulum systems. The resulting equations, which contain the vertical inertia forces, were studied to estimate the influence of these forces on the isolator’s behavior. The nonlinear equation is solved employing the technique of successive approximations. The results obtained showed that the influence of the vertical inertia forces on structural response is negligible for the case of a long-distance ground motion, while becoming significant for a near-source ground motion. On the other hand, very small values of the isolator’s radius R cause an increase of the aforementioned influence.