1. STUDY ON A SEISMIC ENERGY DISSIPATION HYDRAULIC DEVICE
F. Nedelcuț1,a) , C.-S. Simionescu1, F.-D. Șcheaua1
Engineering and Agronomy Faculty of Brăila, „Dunărea de Jos” University of Galaţi, Romania
Research Center of Mechanical Machines and Technological Equipment (MECMET)
SEISMIC MOVEMENTS. METHODS USED TO LIMIT THEIR EFFECTS
THE PROPOSED DISSIPATION ARRANGEMENT
CONCLUSIONS 1
Fig. 4 Seismic fluid viscous dampers of
1.3 and 2 Million pounds
Fig. 5 A seismic energy dissipation hydraulic device
This hybrid system can accomplish a partial disconnection of the superstructure from the movements of the foundation as the friction bearings can also offer to the foundation a certain amount of displacement; in the same time, the hydraulic system starts playing the role of an anchor point, at the end of the stroke of the friction system device.
Since the proposed system is a hybrid one and has a composite structure, therefore, it is much more complex than a friction pendulum bearings device (FPB), or than a friction viscous device (FVD) used separately, but is also capable of isolating more efficient a wider range of frequencies than the constituent devices.
Never less, the proposed system is also capable of limiting the reactions of both coupled devices simultaneously for a wide variety of seismic ground motions, corresponding to wave patterns for both near‑field and far-field regions of a significant earthquake[3].
Hydraulic devices provide an amount of seismic energy dissipation, but also can be successfully used to limit the superstructure displacements during an earthquake. The composed system is therefore capable of simultaneously limiting the superstructure response, but also when it is necessary to limit the loads, for a large variety of seismic ground motions [3]. This means that such a system can also offer a certain isolation for the movements caused by the everyday heavy‑duty traffic [6].
Șcheaua, F.-D., „Analiza sistemelor de disipare cu frecare uscată la acțiuni dinamice / Behavioral analysis for dry friction dissipation systems at dynamic actions”, Doctoral thesis, Universitatea "Dunărea de Jos" Galați, 2013
Şcheaua, F., Nedelcuț, F., „Energy Dissipation Device Using Fluid Dampers”, The Annals of „Dunărea de Jos” University of Galaţi, Fascicle XIV Mechanical Engineering, ISSN , XX:99-102, 2012
Nedelcuț, F., Şcheaua, F., Axinti, G., „Hydraulic Actuation Used for Bridge Seismic Isolation” Proceedings of the International Conference of Hydraulics and Pneumatics – HERVEX 2014, Section I: Industrial Hydraulics and Mechatronics, ISSN , pp. 29 – 32, 2014
Web site:
Şcheaua, F., Nedelcuț, F., „Hybrid system device for seismic isolation of structures”, Proceedings of the Annual Symposium of the Institute of Solid Mechanics „SISOM 2012” and Session of the Comission of Acoustics, Romanian Academy, Bucharest, mai, 2012
Şcheaua, F., Nedelcuț, F., „Study on a Seismic Isolation Method Suitable for an Architectural Monument”, The Annals of „Dunărea de Jos” University of Galaţi, Fascicle XIV Mechanical Engineering, ISSN , XIX:81‑86, 201
Seismic actions are of great interest, especially in very dense populated areas, because an earthquake can have strong effects on building structures (Fig.2), including viaducts or bridges.
When estimating these effects on building structures one may find that the main characteristic of these actions is that they present significant inertial forces.
That’s why, when discussing about large structures with large openings, such as bridges, it is advisable that the superstructure should be disconnected from the groundwork.
Fig. 2 The Basarab Viaduct (Romania) is located in an area of a high seismic risk.
Adaptive hybrid isolation systems
The seismic isolation system proposed by the authors is suitable for the seismic isolation of large constructed structures as viaducts or bridges, isolated with friction pendulum systems.
They are composed of two kinds of passive isolation devices, one based on mechanical friction force and the other based on viscous fluid friction.
This isolating purpose system combines two actions:
one - accomplished by the friction bearings - of sliding over a concave surface, when the own weight of the structure, acting vertically creates a horizontal resistance force, and
a second - created by the viscous fluid dampers - of adding a drag force along the structural elements which are attached to, Fig. 1 [2], Fig.4 and Fig. 5.
Hybrid system. Construction details
Through the piston head were drilled a number of outlets in order to allow fluid to flow between the cylinder chambers.
The pressure difference between the two chambers will cause silicone-oil to flow through the orifices made in the piston head and therefore the seismic energy is transformed into heat, which dissipates.
When used paired with a hydraulic motion damper, PF adapts to the earthquake motions and displacements.
The smaller the displacement, the higher frequency ground motions are absorbed by the pendulum, while the movement period of the building is shortened [5].
Fig. 1 A hybrid base-isolated viaduct structure, including friction pendulum bearing systems, elastomeric systems and hydraulic fluid dampers
Current methods used to limit the effects of the seismic forces
Therefore, in order to protect bridges from earthquake damages, seismic isolation technology has to be applied. One frequently used method is to use friction bearing systems.
A newer variant uses a specific hybrid seismic isolation system, composed of a friction system based on a friction pendulum bearing (FPB) and a hydraulic fluid damper of a friction viscous device (FVD) type [1], in order to provide supplementary energy dissipation (Fig. 1).
In order to use such hybrid seismic isolation system, the bridges must be constructed with supports with slip, as with dissipative systems, of both friction and hydraulic types.
Fig. 6 The pressure diagram for a 12-holes piston head arrangement
Fig. 3 The 3D model of the fluid damper of a friction viscous device (FVD) type
REFERENCES
CFD analysis
CFD analysis was conducted in Ansys Flowizard software. The analysis evaluated the pressures, velocities and forces inside the fluid viscous damper device during a 5Hz seismic oscillation, typical for ground movements.
Then, with Fluent Flowizard, as a CFD solver program, were solved the pressures and forces developed into this model. Using the 3D model presented in Fig. 3, the calculation converged to a stable solution (Fig. 6 and Fig. 7)
Simplified hydraulic device model
In order to have higher viscous resistant forces, the hydraulic system is a plunger-cylinder type filled with fluid having high viscosity and low compressibility factor (usually a mineral- or silicone-type oil).
In this study case, the stainless steel piston moves in a chamber filled with a high viscosity silicone oil.
For a higher damping effect, we selected a high‑viscosity silicone-oil type fluid is a, having a density of kg/m3 and a dynamic viscosity of 29.1 kg·m-1s-1. Such fluid viscous dampers (FVD) may operate in temperature fluctuations ranging from ‑40˚ C to +70˚ C.
The chosen silicone-oil is nontoxic, nonflammable, inert and stable for extremely long periods of time [4].
A HYBRID SEISMIC ISOLATION SYSTEM
These hydraulic fluid damper systems act as a special safety devices acting mainly at the end of the stroke and play the role of anchoring points for the structure.
Researches presented by the authors concentrate on the analysis and implementation of such adaptive hybrid isolation system.
Fig. 3 presents the 3D model of the above mentioned hydraulic dissipation device, mounted as a bridge or viaduct seismic isolation.
Fig. 7 The axial speed diagram for a 12-holes piston head arrangement