Practical method of obtaining different levels of seismic energy dissipation using viscous fluid protective system on bridges

Abstract

In order to achieve an optimal stability performance during transient vibratory actions the damping method is used for the bridge structures. Conventional approach would dictate that a structure must inherently attenuate or dissipate the effects of transient inputs through a combination of strength, flexibility and deformity. The damping level is being at low values at a conventional elastic structure and hence the amount of dissipated energy during transient vibratory actions is also in very low value. In the event of an earthquake, conventional structures usually perform high deformations which when situated beyond their elastic limits can cause the collapse. In such cases most of the dissipated energy amount is absorbed by the structure through localized damage as it fails. The concept of supplemental dampers added to a structure assumes that most of the energy amount input to the structure from a transient vibratory action will be absorbed, not by the structure itself, but rather by supplemental damping elements. Properly implemented, an energy dissipation system can be able to simultaneously reduce both stress and deflection within the structure elements. The fluid viscous protective system concept is presented as an optimum energy dissipation solution for bridge structure types. The operation of these devices is on the hydro-static principle of fluid flow through orifices of a special diameter value. In this paper it is presented an innovative functional and constructive model of fluid viscous device based on a practical design method which allows the controlled operation regime regarding the viscous fluid flow inside the device cylinder being able to provide considerable resistant force levels to relative motions between a bridge structural frames where is mounted and achieving considerable amounts of seismic energy dissipation when an earthquake occurs. For the constructive method of fluid viscous system model is adopted a practical constructive method aiming the direct control on the circulated fluid flow rate so that the device response force should be considerably larger, acting for limiting the relative movement of the structural frames and without introducing additional stiffness to the structural system to which it is attached, due to the elasticity of the working fluid type used. It represents an innovative method because of the special design orifices for fluid flow rate control used which, depending on the specific diameter values, can provide device different response force values and implicitly different dissipated energy amount levels based on the characteristic represented by the resistant force variation law according to the piston stroke.