US20070283635A1

US20070283635A1 - Seismic control bearing device and seismic control system including the same

Info

Publication number: US20070283635A1
Application number: US11/734,310
Authority: US
Inventors: Jong-Seh Lee; In-Ho Hwang; Jong-Hyuk Lim
Original assignee: Individual
Current assignee: Industry University Cooperation Foundation IUCF HYU
Priority date: 2006-06-13
Filing date: 2007-04-12
Publication date: 2007-12-13
Also published as: KR20070118758A

Abstract

Provided are a seismic control bearing device capable of absorbing and/or blocking vibration energy transmitted to structures due to earthquakes, and so on, as well as actively controlling various dynamic behaviors generated from the structures with low power and without additional equipment, and a seismic control system including the same. The seismic control bearing device is installed between a ground base and a structure constructed on the ground base to reduce vibration energy applied to the structure, and includes a plurality of deposition members spaced apart from each other; and a plurality of magneto-sensitive members disposed between the deposition members and formed of a magneto-sensitive material. The properties including a stiffness coefficient and an damping coefficient of the magneto-sensitive material are varied depending on a variation of a magnetic field formed around the magneto-sensitive member.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2006-0052880, filed on Jun. 13, 2006, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a seismic control bearing device and a seismic control system including the same, and more particularly, to a seismic control bearing device installed in structures such as buildings, bridges, and so on, and capable of reducing vibration energy transmitted to the structures by seismic load, and a seismic control system including the same.
2. Description of the Related Art
In recent times, research on seismic isolation devices has been widely attempted to protect structures such as buildings, bridges, and so on, by absorbing and/or blocking vibration energy applied to the structures using additional equipment. A base isolation device such as an elastomer bearing, a lead rubber bearing, a sliding bearing, and so on has been developed as a representative seismic isolation device. FIG. 1 illustrates a lead rubber bearing 1 installed between a ground base 50 and a structure 60.
However, a seismic-resistant design using the seismic isolation device increases a natural frequency of a structure system, constituted of a base isolation device and a structure to increase relative displacement response of the structure, thereby causing disadvantages in usability and design of the base isolation device. In addition, it is known that the above seismic-resistance design is inappropriate for broad input earth movement due to dynamic characteristics having strong non-linearity. For example, a base isolation device designed for the El Centro Earthquake may not show seismic isolation performance when a predominant frequency of seismic load is varied, a seismic center is near, a wave velocity is fast, and a seismic cycle is large, like the Mexico City earthquake.
Recently, a hybrid controller combining a base isolation device with an active device has been developed. The hybrid controller can effectively reduce vibration energy of various input loads in comparison with a manual controller. In addition, the hybrid controller can also control a multi-vibration mode of the structure. However, addition of the active controller can increase costs because of high-capacity external power, and it is difficult to obtain reliability of equipment for a long time.
On the other hand, since a semi-active controller using a control fluid provides performance similar to the active controller and requires small electric power, vibration control devices using an electro-rheological (ER) fluid and a magneto-rheological (MR) fluid have been developed since 1992, and functionality of the semi-active controller has been confirmed through small-scale model experiments. Especially, an MR fluid damper that can operate with a lower power than an ER fluid damper has been continuously researched since 1994. Recently, equipment of about 20-ton size has been developed. However, as shown in FIG. 2, since the semi-active controller, for example, the MR fluid damper 2, should be installed with the base isolation device such as the lead rubber bearing 1, it is difficult to adapt the MR fluid damper to an actual structure for economic reasons.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a seismic control bearing device capable of absorbing and/or blocking vibration energy transmitted to structures due to earthquakes, and so on, as well as actively controlling various dynamic behaviors generated from the structures with low power and without additional equipment, and a seismic control system including the same.
In one aspect, the invention is directed to a seismic control bearing device installed between a ground base and a structure constructed on the ground base to reduce vibration energy applied to the structure. The seismic control bearing device includes a plurality of deposition members spaced apart from each other; and a plurality of magneto-sensitive members disposed between the deposition members and formed of a magneto-sensitive material. The properties including a stiffness coefficient and an damping coefficient of the magneto-sensitive material are varied depending on a variation of a magnetic field formed around the magneto-sensitive material.
In another aspect, the invention is directed to a seismic control system including: a sensing unit for sensing dynamic behavior of a structure and outputting a sensing signal corresponding to dynamic vibration of the structure; a seismic control bearing device installed between the structure and a ground base, on which the structure is constructed, to reduce vibration energy applied to the structure, wherein the seismic control bearing device includes a plurality of deposition members spaced apart from each other; and a plurality of magneto-sensitive members disposed between the deposition members and formed of a magneto-sensitive material; a magnetic field forming unit for generating a variation of a magnetic field in the seismic control bearing device such that the properties including a stiffness coefficient and an damping coefficient of the magneto-sensitive material are varied depending on the variation of the magnetic field; and a control unit for receiving a sensing signal from the sensing unit to control the magnetic field forming unit such that the seismic control bearing device generates a seismiccontrol force for reducing vibration energy of the structure on the basis of the sensing signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will become more apparent from the following more particular description of exemplary embodiments of the invention and the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a schematic cross-sectional view of a conventional seismic isolation bearing device installed in a structure.

FIG. 2 is a schematic cross-sectional view of a conventional magneto-rheological (MR) damper installed in a structure with a seismic isolation bearing device.

FIG. 3 is a schematic cross-sectional view of a seismic control bearing device installed in a structure in accordance with an exemplary embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a magnetic field formed in the seismic control bearing device shown in FIG. 3.

FIG. 5 is an enlarged view of portion “A” of FIG. 4.

FIG. 6 is a schematic block diagram of a seismic control system including the seismic control bearing device in accordance with an exemplary embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of a seismic control bearing device in accordance with another exemplary embodiment of the present invention.

FIG. 8 is a view showing a dynamic model of a base isolation device.

FIG. 9 is a schematic view of a five-floor building having six degrees of freedom.

FIG. 10 is a graph showing ground acceleration and Fast Fourier Transform of the El Centro Earthquake.

FIG. 11 is a graph showing ground acceleration and Fast Fourier Transform of the Kobe Earthquake.

FIG. 12 is a graph showing ground acceleration and Fast Fourier Transform of the Northridge Earthquake.

FIG. 13 is a graph showing dynamic behavior of the El Centro Earthquake.

FIG. 14 shows a displacement-force curve of the El Centro Earthquake.

FIG. 15 is a graph showing dynamic behavior of the Kobe Earthquake.

FIG. 16 shows a displacement-force curve of the Kobe Earthquake.

FIG. 17 is a graph showing dynamic behavior of the Northridge Earthquake.

FIG. 18 shows a displacement-force curve of the Northridge Earthquake.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.
FIG. 3 is a schematic cross-sectional view of a seismic control bearing device installed in a structure in accordance with an exemplary embodiment of the present invention, FIG. 4 is a schematic cross-sectional view of a magnetic field formed in the seismic control bearing device shown in FIG. 3, FIG. 5 is an enlarged view of portion “A” of FIG. 4, and FIG. 6 is a schematic block diagram of a seismic control system including the seismic control bearing device in accordance with an exemplary embodiment of the present invention.
Referring to FIGS. 3 to 6, a seismic control system 100 in accordance with an exemplary embodiment of the present invention includes a pair of seismic control bearing devices 10, a magnetic field forming unit 20, a sensing unit 30, and a control unit 40.
As shown in FIG. 3, each bearing device 10 is installed between a ground base 50 and a structure 60. The structure 60, for example, a building, a bridge, and so on, is constructed on the ground base 50. The ground base 50 is generally installed on the ground 51 using concrete, etc. The seismic control bearing device 10 functions to block direct transmission of an earthquake occurring from the seismic center to the structure 60 and to absorb vibrations generated from the earthquake. The seismic control bearing device 10 includes a plurality of deposition members 11 and a plurality of magneto-sensitive members 12.
The deposition members 11 are disposed apart from each other. Each of the deposition members 11 is formed of a plate-shaped metal member, for example, a steel plate.
The magneto-sensitive members 12 are disposed between the deposition members 11. Each of the magneto-sensitive members 12 has a plate shape, similar to the deposition member 11. Each magneto-sensitive member 12 is formed of a magneto-sensitive material, in which the properties such as a stiffness coefficient and an damping coefficient are varied depending on a variation of the magnetic field. The magneto-sensitive material includes a rubber matrix 121 and metal particles 122. The rubber matrix 121 may be formed of rubber, for example, natural rubber, polyurethane, and so on. The metal particles 122 are formed of a metal material such as iron particles, and dispersed in the rubber matrix 121. In the embodiment the magneto-sensitive material is manufactured by evenly mixing natural rubber with iron particles at about 120° C., filling the mixture into a mold, and curing the mixture under an electro-magnetic field of 0.7 T for thirty minutes.
The properties of the magneto-sensitive material vary depending on a variation of a magnetic field formed around the magneto-sensitive member 12. That is, as shown by an arrow in FIG. 4, when the magnetic field is formed around the magneto-sensitive member 12, the metal particles 122 dispersed in the rubber matrix are re-aligned to a direction of the magnetic field to vary the properties of the magneto-sensitive material such as a stiffness coefficient, an damping coefficient, and so on. For example, when the strength and/or direction of the magnetic field are varied, the stiffness coefficient and the damping coefficient of the magneto-sensitive member 12 are also varied. As described above, the variation of the properties of the magneto-sensitive material was introduced by Jacob Rainbow in 1948. In addition, the above variation is disclosed in the papers of Kordonsky, W. (1993), “Magneto-rheological effects as a base of new devices and technologies”, J. Mag. & Mag. Mat, Vol. 122, pp. 395-398; Jolly, M. R., Carlson, J. D. and Munoz, B. C. (1996), “A model of the behavior of magneto-rheological materials”, Smart Material Structures, Vol. 2, pp. 607-614; Carlson J. D. and Jolly M. R. (2000), “MR fluid, form and elastomer devices”, Mechatronics, Vol. 10, pp. 55-69, and so on.
The magnetic field forming unit 20 generates a variation of the magnetic field in the seismic control bearing device 10. The magnetic field forming unit 20 includes a coil member 21 and a current supply part 22. The coil member 21 has an annular shape to surround the seismic control bearing device 10. The current supply part 22 supplies current to the coil member 21. When current is applied to the coil member 21, a magnetic field is formed around the coil member 21, as shown in FIG. 4.
The sensing unit 30 is attached to the structure 60 to sense dynamic vibrations of the structure 60. In addition, the sensing unit 30 outputs a sensing signal corresponding to dynamic behavior of the structure 60 as an electrical signal. The sensing signal includes displacement, acceleration, ground acceleration, and a vibration cycle of the structure. More specifically, the sensing signal includes horizontal displacement, horizontal acceleration, horizontal ground acceleration, and a horizontal vibration cycle of the structure. In addition, the sensing unit 30 continuously outputs sensing signals corresponding to the dynamic behavior of the structure until the earthquake is disappeared after the earthquake occurs.
The control unit 40 controls the magnetic field forming unit 20 to control a magnetic field formed around the seismic control bearing device 10. First, the control unit 40 receives a sensing signal from the sensing unit 30. Next, the control unit 40 calculates a seismic control force for reducing vibration energy generated from the structure 60 on the basis of the sensing signal. Preferably, the control unit 40 calculates a control force that can minimize the vibration energy generated from the structure. More specifically, the control force is calculated by minimizing a performance index J, which will be described in the following description of numerical analysis. In the embodiment, the control unit 40 is configured to include a linear quadratic (LQ) regulator, which is well known. As described above, after calculating and setting the control force, the control unit 40 controls the magnetic field forming unit 20 to drive the seismic control bearing device 10 to generate the control force. Here, since the properties of the seismic control bearing device 10, especially, a stiffness coefficient and an damping coefficient of the magneto-sensitive member 12 are varied depending on a variation of the magnetic field formed around the seismic control bearing device 10, the control unit 40 controls the seismic control bearing device 10 to perform the calculated control force by forming an appropriate magnetic field in the seismic control bearing device 10. That is, the control unit 40 controls an amount of current supplied from the current supply part 22 to control the strength of a magnetic field formed around the coil member 21, thereby adjusting the control force of the seismic control bearing device 10.
For example, the control unit 40 controls the current supply part 22 not to supply current during normal times when there is no seismic wave transmitted to the structure 60. In addition, when a seismic wave is transmitted to the structure 60, the control unit 40 calculates a control force for minimizing vibration energy of the structure 60 on the basis of the sensing signal, and appropriately controls an amount of current supplied to the coil member 21 from the current supply part 22 to vary the strength of a magnetic field formed around the seismic control bearing device 10, thereby controlling the seismic control bearing device 10 to perform the control force. Therefore, it is possible to actively control dynamic behavior of the structure due to the earthquake. In addition, the control unit 40 controls supply of current of the current supply part 22 corresponding to the sensing signal continuously input until the earthquake is disappeared after the earthquake occurs, thereby controlling the dynamic behavior of the structure 60 until the earthquake is disappeared after the earthquake occurs.
Hereinafter, in the seismic control system 100 in accordance with an exemplary embodiment of the present invention, when a dynamic load due to the earthquake is applied to the structure 60, an example of a process of reducing vibration energy of the structure 60 and controlling dynamic behavior of the structure will be described with reference to FIG. 6. Dotted arrows shown in FIG. 6 represent a moving path of vibration energy due to the earthquake, sensing of dynamic behavior of the structure, and a control force of the seismic control bearing device 10.
During normal times when there is no earthquake, since the control unit 40 controls the current supply part 22 not to supply current to the coil member 21, there is no magnetic field generated around the seismic control bearing device 10. When an earthquake occurs in this state, current is applied to the coil member 21 at substantially the same time the earthquake occurs to form a magnetic field around the coil member 21. The magnetic field provides a control force such that the seismic control bearing device 10 can minimize vibration energy of the structure 60, thereby optimally controlling dynamic behavior of the structure 60, which will be described in detail.
When an earthquake occurs, the sensing unit 30 attached to the structure 60 senses horizontal displacement, horizontal acceleration, horizontal ground acceleration, and a horizontal vibration cycle of the structure 60, and outputs a sensing signal including the displacement, acceleration, ground acceleration and vibration cycle to the control unit 40 as an electrical signal. The control unit 40 calculates a control force that can minimize vibration energy of the structure 60 on the basis of the sensing signal, and then determines the strength of a magnetic field to be formed around the seismic control bearing device 10 to perform the control force. Next, the control unit 40 controls an amount of current supplied to the coil member 21 from the current supply part 22 to form the magnetic field. As described above, when the current is supplied to the coil member 21, as shown in FIG. 4, a magnetic field is formed around the seismic control bearing device 10 to re-align the metal particles dispersed in the magneto-sensitive material in a direction of the magnetic field. As a result of the realignment of the metal particles, the properties of the magneto-sensitive material, i.e., a stiffness coefficient and an damping coefficient are varied to vary seismic control performance of the seismic control bearing device 10. As described above, when the properties of the magneto-sensitive material vary depending on a variation of the magnetic field, it is possible to actively control various types of vibrations applied to the structure 60. Especially, there is no need to use a large amount of power, unlike the conventional active control system. In addition, it is possible to accomplish the same semi-active control and base isolation performance as the conventional art through a single seismic control bearing device 10, unlike the conventional system including the semi-active controller and the base isolation device.
Meanwhile, the control unit 40 controls current supply of the current supply part 22 corresponding to the sensing signal continuously input until the earthquake is disappeared after the earthquake occurs, to vary the seismic control performance of the seismic control bearing device 10 to correspond to the sensing signal, thereby continuously controlling dynamic behavior of the structure 60 until the earthquake is disappeared after the earthquake occurs.
As described above, the seismic control bearing device 10 in accordance with an exemplary embodiment of the present invention absorbs and/or blocks vibration energy transmitted to the structure due to shear deformation, similar to the conventional base isolation device, for example, the lead rubber bearing. In addition, adjustment of the strength of the magnetic field varies properties of the seismic control bearing device 10, for example, a stiffness coefficient and an damping coefficient, thereby enabling semi-active control of dynamic behavior of the structure.
Meanwhile, numerical analysis for checking seismic control performance of the seismic control system including the seismic control bearing device in accordance with an exemplary embodiment of the present invention was performed. The numerical analysis was performed for a five-floor building having six degrees of freedom used by Kelly et al. in 1987. In addition, evaluation of performance and semi-active control of the seismic control system as a base isolation device was performed by obtaining responses of the seismic control system to the El Centro Earthquake, the Kobe Earthquake, and the Northridge Earthquake, each having different characteristics. Further, in order to analyze effectiveness of the base isolation device, the numerical analysis was performed with respect to the following three cases, 1) a structure which is uncontrolled and base-supported, 2) a structure in which a lead rubber bearing is installed, and 3) a structure in which a seismic control bearing device is installed.
First, an equation of motion of the base isolation device such as the seismic control bearing device and the conventional lead rubber bearing is obtained. As shown in FIG. 8, an equation of motion of a model, from which the ground base and the structure are separated, is calculated as follows.
M{umlaut over (x)}+C{dot over (x)}+Kx=Λf−M{umlaut over (x)} _g
Here, f and Λ=[1 0]^Trepresent an additional force by the base isolation device and a position vector. x _g represents a seismic load, and x=[x_bx_s]^Trepresents displacement of the ground base and the structure. In addition, matrix of mass M, damping C and stiffness K is as follows.
$M = [\begin{matrix} m_{b} & 0 \\ 0 & m_{s} \end{matrix}], C = [\begin{matrix} c_{b} + c_{s} & - c_{s} \\ - c_{s} & c_{s} \end{matrix}], K = [\begin{matrix} k_{b} + k_{s} & - k_{s} \\ - k_{s} & k_{s} \end{matrix}]$
Here, m_band m_srepresent masses of the ground base and the structure, c_band k_brepresent an damping coefficient and a stiffness coefficient of the ground base, and c_sand k_srepresent an damping coefficient and a stiffness coefficient of the structure.
A state parameter q is defined as q=[x^T{dot over (x)}^T]^Tto represent the base isolation device as the following state spatial equation
{dot over (q)}=Aq+Bf+E{umlaut over (x)} _g
Here, A, B and E represent a system matrix, a control matrix, and a disturbance matrix, which are as follows.
$A = [\begin{matrix} 0 & I \\ - M^{- 1} K & - M^{- 1} C \end{matrix}], B = [\begin{matrix} 0 \\ - M^{- 1} A \end{matrix}], E = [\begin{matrix} 0 \\ - 1 \end{matrix}] .$
Next, as shown in FIG. 9, the structure, in which the seismic control bearing device in accordance with the present invention is installed, was modeled as a five-floor building. Mass, a stiffness coefficient, and an damping coefficient of the five-floor building are as described in Table 1. The uncontrolled and base fixed structure has an damping of 2% and a natural frequency of 0.3 seconds in a first mode. While dynamic non-linearity of the structure was ignored, excessive structural movement was substantially considered.

TABLE 1

	Mass of each floor	Stiffness of each	Damping of each
Position	[kg]	floor [kN/m]	floor [kNs/m]

Ground base	m_b= 6800	k_b= 231.5	c_b= 3.74
First floor	m₁= 5897	k₁= 33732	c₁= 67
Second floor	m₂= 5897	k₂= 29093	c₂= 58
Third floor	m₃= 5897	k₃= 28621	c₃= 57
Fourth floor	m₄= 5897	k₄= 24954	c₄= 50
Fifth floor	m₅= 5897	k₅= 19059	c₅= 38

In addition, the lead rubber bearing was designed to have a yield force of 14.38 kN. A hysteresis restoring force f_LRBand a non-dimensional hysteresis parameter z to be used in the numerical analysis are obtained by the following formulae.
f _LRB =Q _pb +k _b x _b +c _b {dot over (x)} _b
ż=−γ|{dot over (u)} _b |z|z| ⁿ⁻¹ −β{dot over (u)} _b |z| ⁿ +A{dot over (u)} _b
Here, Q_pbis a yield load of lead, and is obtained by Q_pb=(1−K_yield/K_initial)·Q_y. Q_yis assumed as 5% of the total weight of the structure, and parameter values used in the lead rubber bearing, for example, a stiffness ratio of before/after yield of lead β, γ, a non-dimensional parameter A, an integer coefficient n is used for design parameters described in Table 2, as disclosed in Ramallo (2002), “Smart” Base Isolation Systems (2002) Journal of Engineering Mechanics Vol. 128. No. 10 pp. 1088-1099.

TABLE 2

Parameter	Value	Parameter	Value

Qpb	14.48(kN)	γ	38.37
Qy	18.14(kN)	A	76.74
K_yield/K_initial	6	n	1
		β	−38.37

Next, in order to enable semi-active control of the seismic control bearing device, an active controller was first designed. In order to design the active controller, Q and R values were obtained to minimize a performance index J.
$J = \int_{0}^{\infty} (z^{T} Qz + F^{T} RF) \partial t$
The Q value and the R value were obtained through a trial and error method and used as follows.
$\begin{matrix} R = \frac{1}{{(22 kN)}^{2}} \\ = \frac{1}{{(22000)}^{2}}, \end{matrix}$ $Q = diag (\begin{matrix} q_{drifts}^{'} I & 0 \\ 0 & q_{accels}^{'} I \end{matrix})$ $Here, q_{drifts}^{'} = 33.1, q_{accels}^{'} = 99.3$
In addition, in order to convert the active controller into the semi-active controller, when the magnetic field is not applied, a basic damping force of the seismic control bearing device was set as 1 kN, and when the magnetic field is applied, a maximum damping force of seismic control bearing device was set as 200 kN, using a clipped-optimal control algorithm.
Finally, a seismic load to be input into the structure was set as three types, i.e., the El Centro Earthquake, the Kobe Earthquake, and the Northridge Earthquake. The El Centro Earthquake is a first severe earthquake recorded by an accelerometer and has been considered as a reference earthquake for research and designs of a seismic-resistant design standard or a base isolation device. The Kobe Earthquake is an earthquake in a sedimentary ground similar to the Mexico City, a shallow earthquake generated from underground of about 20 km, and a typical severe earthquake occurring just below the city and having a maximum ground acceleration of 0.83 g. The Northridge Earthquake was a severe earthquake with a magnitude of 6.8 which generated by reverse fault movement. The Northridge Earthquake became a direct cause for currently performed worldwide seismic design development.
As described above, after preparing the numerical analysis, performance of the conventional lead rubber bearing and the seismic control bearing device was evaluated. In the numerical analysis, accelerogram and Fast Fourier Transform (FFT) of the respective earthquakes used in an input seismic load are described in FIGS. 10 to 12, and properties of the respective earthquakes are described in Table 3.

TABLE 3

		Recording	Predominant
	Date of	Time	Frequency		PGA
Earthquake	Occurrence	(sec)	(Hz)	Magnitude	(g)

El Centro	1940.5.18	50	1.5	7.1	0.35
Kobe	1995.1.17	50	1.3	7.2	0.833
Northridge	1994.1.17	40	0.63	6.8	0.843

Performing the numerical analysis through the above processes and comparing performance of the seismic control bearing device and the lead rubber bearing, showing their ability in the El Centro Earthquake, the Kobe Earthquake, and the Northridge Earthquake, when strength of maximum ground acceleration is applied, with maximum base displacement, maximum acceleration of the uppermost floor, and relative displacement between first and second floors, the following result can be obtained. In FIGS. 13 to 18, LRB represents the result of the structure in which the lead rubber bearing is installed, Active represents the result of the active-controlled structure, Fixed represents the result of the structure to which the ground base is fixed, and MS rubber represents the result of the structure in which the seismic control bearing device in accordance with an exemplary embodiment of the present invention is installed.
First, reviewing dynamic behavior of the El Centro Earthquake, as shown in FIG. 13, the seismic control bearing device has a base displacement of 28 cm smaller than 30 cm of the lead rubber bearing by about 2 cm. The seismic control bearing device has an uppermost floor acceleration of 0.191 g, which is reduced by about 84% in comparison with the base fixed structure, and the lead rubber bearing has an uppermost floor acceleration of 0.542 g, which is reduced by about 55% in comparison with the base fixed structure. The seismic control bearing device has a relative displacement between first and second floors of 1.5 mm, which is reduced by 80% or more in comparison with the base fixed structure, and the lead rubber bearing has a relative displacement between first and second floors of 2.7 mm, which is reduced by about 68% or more in comparison with the base fixed structure. As described above, it will be appreciated that the seismic control bearing device has a better relative displacement between floors than the lead rubber bearing.
In addition, FIG. 14 illustrates the relationship between displacement and damping force of the lead rubber bearing and the seismic control bearing device in the El Centro Earthquake. The lead rubber bearing has an damping force of about 80.94 kN, and the seismic control bearing device has an damping force of about 119 kN.
Next, base displacement, uppermost floor acceleration, and relative displacement between first and second floors of the Kobe Earthquake as a near earthquake were compared. As shown in FIG. 15, the seismic control bearing device has a base displacement of 36.1 cm smaller than 43.3 cm of the lead rubber bearing by about 7 cm. The seismic control bearing device has an uppermost floor acceleration of 0.244 g, which is reduced by about 92% in comparison with the base fixed structure, and the lead rubber bearing has an uppermost floor acceleration of 0.372 g, which is reduced by about 88% in comparison with the base fixed structure. The seismic control bearing device has a relative displacement between first and second floors of 1.95 mm, which is reduced by 90% or more in comparison with the base fixed structure, and the lead rubber bearing has a relative displacement between first and second floors of 9.61 mm, which is reduced by about 50% or more in comparison with the base fixed structure. As described above, it will be appreciated that the seismic control bearing device has a better relative displacement between floors than the lead rubber bearing.
FIG. 16 illustrates the relationship between displacement and damping force of the lead rubber bearing and the seismic control bearing device in the Kobe Earthquake. The lead rubber bearing has a maximum damping force of about 98.98 kN, and the seismic control bearing device has a maximum damping force of about 190.57 kN.
Finally, base displacement, uppermost floor acceleration, and relative displacement between first and second floors of the Northridge Earthquake were compared. As shown in FIG. 17, the seismic control bearing device has a base displacement of 81 cm smaller than 97.9 cm of the lead rubber bearing by about 17 cm. The seismic control bearing device has an uppermost floor acceleration of 0.543 g, which is reduced by about 86% in comparison with the base fixed structure, and the lead rubber bearing has an uppermost floor acceleration of 0.815 g, which is reduced by about 80% in comparison with the base fixed structure. The seismic control bearing device has a relative displacement between first and second floors of 4.3 mm, which is reduced by 83% or more in comparison with the base fixed structure, and the lead rubber bearing has a relative displacement between first and second floors of 6.6 mm, which is reduced by about 74% or more in comparison with the base fixed structure.
FIG. 18 illustrates the relationship between displacement and damping force of the lead rubber bearing and the seismic control bearing device in the Northridge Earthquake. The lead rubber bearing has a maximum damping force of about 204.98 kN, and the seismic control bearing device has a maximum damping force of about 341.17 kN.
Entirely reviewing the above results, as shown in Tables 4 and 5, it will be appreciated that the seismic control bearing device in accordance with the present invention has a remarkably better performance in all kinds of earthquakes than the conventional lead rubber bearing.

TABLE 4

		Seismic control bearing
Base fixed	Lead rubber bearing	device

El			El			El
Centro	Kobe	Northridge	Centro	Kobe	Northridge	Centro	Kobe	Northridge

Maximum	—	—	—	0.305	0.433	0.979	0.282	0.361	0.811
base
displacement
Uppermost	1.197	2.986	4.008	0.542	0.372	0.815	0.191	0.244	0.543
floor
acceleration
(g)
Relative	0.00836	0.019	0.0251	0.00277	0.0096	0.0066	0.0015	0.002	0.0043
displacement
between
first and
second floors

TABLE 5

		Relative
Maximum	Uppermost	displacement
base	maximum	between first and
displacement	acceleration	second floors

		Seismic		Seismic		Seismic
		control		control		control
		bearing		bearing		bearing
Earthquake	LRB	device	LRB	device	LRB	device

El Centro	—	7%	(55%)	65%(84%)	(68%)	46%(80%)
(0.350 g)
Kobe	—	17%	(88%)	34%(92%)	(50%)	79%(90%)
(0.83 g)
Northridge	—	17%	(80%)	33%(86%)	(74%)	35%(83%)
(0.843 g)

*Numbers in ( ) represent response reduction effect of the base fixed structure.

While the seismic control bearing device in accordance with the present invention includes a plurality of deposition members and a plurality of magneto-sensitive members, a seismic control bearing device 10 a may be configured as shown in FIG. 7. That is, the seismic control bearing device 10 a may further include a core member 13, different from FIG. 4. The core member 13 is configured to pass through the deposition members 11 and the magneto-sensitive members 12. In addition, the core member 13 is formed of a metal member such as lead. The core member 13 functions to absorb vibrations applied to the structure 60.
Exemplary embodiments of the present invention have been described, but are not limited thereto. In addition, various modifications may be made by those skilled in the art.
For example, in the embodiment, while the seismic control bearing device of the present invention is configured such that the strength of a magnetic field is varied depending on a variation of an amount of current and properties of the magneto-sensitive material are varied depending on the variation of the strength of the magnetic field, the properties of the magneto-sensitive material may be varied by changing a direction of the magnetic field formed around the seismic control bearing device.
In addition, in the embodiment, while a single core member is disposed, a plurality of coil members may be disposed around the seismic control bearing device to make directions of the magnetic fields generated from the coil members different from each other.
As can be seen from the foregoing, it is possible for a seismic control bearing device in accordance with the present invention to actively control various types of dynamic loads generated from the structure by varying properties of a magneto-sensitive material depending on a variation of a magnetic field. In addition, the seismic control bearing device in accordance with the present invention does not need to use a large amount of power, unlike the conventional active controller, and it is possible to perform the same semi-active control and base isolation performance as the conventional art through a single seismic control bearing device, without installing a semi-active controller and a base isolation device of the conventional art.
Exemplary embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.

Claims

1. A seismic control bearing device installed between a ground base and a structure constructed on the ground base to reduce vibration energy applied to the structure, comprising:

a plurality of deposition members spaced apart from each other; and

a plurality of magneto-sensitive members disposed between the deposition members and formed of a magneto-sensitive material,

wherein properties of including a stiffness coefficient and an damping coefficient of the magneto-sensitive material are varied depending on a variation of a magnetic field formed around the magneto-sensitive member.

2. The seismic control bearing device according to claim 1, wherein the magneto-sensitive material comprises a rubber matrix formed of rubber, and metal particles dispersed in the rubber matrix.

3. The seismic control bearing device according to claim 2, wherein the metal particles are iron particles.

4. The seismic control bearing device according to claim 3, wherein the deposition member is formed of a plate-shaped metal material, and the magneto-sensitive member has a plate shape.

5. The seismic control bearing device according to any one of claims 1 to 4, further comprising a core member passing through the deposition members and the magneto-sensitive members and formed of a metal material.

6. A seismic control system comprising:

a sensing unit for sensing dynamic behavior of a structure and outputting a sensing signal corresponding to dynamic vibration of the structure;

a seismic control bearing device installed between the structure and a ground base, on which the structure is constructed, to reduce vibration energy applied to the structure, wherein the seismic control bearing device comprises a plurality of deposition members spaced apart from each other, and a plurality of magneto-sensitive members disposed between the deposition members and formed of a magneto-sensitive material;

a magnetic field forming unit for generating a variation of a magnetic field in the seismic control bearing device such that properties including a stiffness coefficient and an damping coefficient of the magneto-sensitive material are varied depending on the variation of the magnetic field; and

a control unit for receiving a sensing signal from the sensing unit to control the magnetic field forming unit such that the seismic control bearing device generates a seismic control force for reducing vibration energy of the structure on the basis of the sensing signal.

7. The seismic control system according to claim 6, wherein the magneto-sensitive material comprises a rubber matrix formed of rubber, and metal particles dispersed in the rubber matrix.

8. The seismic control system according to claim 7, wherein the bearing device further comprises a core member passing through the deposition members and the magneto-sensitive members and formed of a metal material.

9. The seismic control system according to any one of claims 6 to 8, wherein the sensing signal comprises displacement, acceleration, and a vibration cycle of the structure.

10. The seismic control system according to any one of claims 6 to 8, wherein the magnetic field forming unit comprises an annular coil member disposed to surround the seismic control bearing device, and a current supply part for supplying current to the coil member to form a magnetic field around the coil member.

11. The seismic control system according to claim 10, wherein the control unit controls strength of the magnetic field formed by the magnetic field forming unit by controlling an amount of current supplied from the current supply part.