U.S. patent application number 11/734310 was filed with the patent office on 2007-12-13 for seismic control bearing device and seismic control system including the same.
Invention is credited to In-Ho Hwang, Jong-Seh Lee, Jong-Hyuk Lim.
Application Number | 20070283635 11/734310 |
Document ID | / |
Family ID | 38820467 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070283635 |
Kind Code |
A1 |
Lee; Jong-Seh ; et
al. |
December 13, 2007 |
SEISMIC CONTROL BEARING DEVICE AND SEISMIC CONTROL SYSTEM INCLUDING
THE SAME
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.
Inventors: |
Lee; Jong-Seh; (Seoul,
KR) ; Hwang; In-Ho; (Incheon, KR) ; Lim;
Jong-Hyuk; (Incheon, KR) |
Correspondence
Address: |
LADAS & PARRY LLP
224 SOUTH MICHIGAN AVENUE, SUITE 1600
CHICAGO
IL
60604
US
|
Family ID: |
38820467 |
Appl. No.: |
11/734310 |
Filed: |
April 12, 2007 |
Current U.S.
Class: |
52/167.7 ;
52/167.1; 52/167.2; 52/167.4; 52/167.8 |
Current CPC
Class: |
E04H 9/022 20130101 |
Class at
Publication: |
52/167.7 ;
52/167.1; 52/167.2; 52/167.4; 52/167.8 |
International
Class: |
E04H 9/02 20060101
E04H009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2006 |
KR |
10-2006-0052880 |
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.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] 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
[0002] 1. Field of the Invention
[0003] 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.
[0004] 2. Description of the Related Art
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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
[0009] 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.
[0010] 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.
[0011] 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
[0012] 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.
[0013] FIG. 1 is a schematic cross-sectional view of a conventional
seismic isolation bearing device installed in a structure.
[0014] 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.
[0015] 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.
[0016] FIG. 4 is a schematic cross-sectional view of a magnetic
field formed in the seismic control bearing device shown in FIG.
3.
[0017] FIG. 5 is an enlarged view of portion "A" of FIG. 4.
[0018] 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.
[0019] FIG. 7 is a schematic cross-sectional view of a seismic
control bearing device in accordance with another exemplary
embodiment of the present invention.
[0020] FIG. 8 is a view showing a dynamic model of a base isolation
device.
[0021] FIG. 9 is a schematic view of a five-floor building having
six degrees of freedom.
[0022] FIG. 10 is a graph showing ground acceleration and Fast
Fourier Transform of the El Centro Earthquake.
[0023] FIG. 11 is a graph showing ground acceleration and Fast
Fourier Transform of the Kobe Earthquake.
[0024] FIG. 12 is a graph showing ground acceleration and Fast
Fourier Transform of the Northridge Earthquake.
[0025] FIG. 13 is a graph showing dynamic behavior of the El Centro
Earthquake.
[0026] FIG. 14 shows a displacement-force curve of the El Centro
Earthquake.
[0027] FIG. 15 is a graph showing dynamic behavior of the Kobe
Earthquake.
[0028] FIG. 16 shows a displacement-force curve of the Kobe
Earthquake.
[0029] FIG. 17 is a graph showing dynamic behavior of the
Northridge Earthquake.
[0030] FIG. 18 shows a displacement-force curve of the Northridge
Earthquake.
DETAILED DESCRIPTION OF THE INVENTION
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.degree. C., filling the mixture into a mold, and curing the
mixture under an electro-magnetic field of 0.7 T for thirty
minutes.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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=.LAMBDA.f-M{umlaut over
(x)}.sub.g
[0049] Here, f and .LAMBDA.=[1 0].sup.T represent an additional
force by the base isolation device and a position vector. x.sub. g
represents a seismic load, and x=[x.sub.bx.sub.s].sup.T represents
displacement of the ground base and the structure. In addition,
matrix of mass M, damping C and stiffness K is as follows.
M = [ m b 0 0 m s ] , C = [ c b + c s - c s - c s c s ] , K = [ k b
+ k s - k s - k s k s ] ##EQU00001##
[0050] Here, m.sub.b and m.sub.s represent masses of the ground
base and the structure, c.sub.b and k.sub.b represent an damping
coefficient and a stiffness coefficient of the ground base, and
c.sub.s and k.sub.s represent an damping coefficient and a
stiffness coefficient of the structure.
[0051] A state parameter q is defined as q=[x.sup.T{dot over
(x)}.sup.T].sup.T to represent the base isolation device as the
following state spatial equation
{dot over (q)}=Aq+Bf+E{umlaut over (x)}.sub.g
[0052] Here, A, B and E represent a system matrix, a control
matrix, and a disturbance matrix, which are as follows.
A = [ 0 I - M - 1 K - M - 1 C ] , B = [ 0 - M - 1 A ] , E = [ 0 - 1
] . ##EQU00002##
[0053] 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-US-00001 TABLE 1 Mass of each floor Stiffness of each Damping
of each Position [kg] floor [kN/m] floor [kNs/m] Ground base
m.sub.b = 6800 k.sub.b = 231.5 c.sub.b = 3.74 First floor m.sub.1 =
5897 k.sub.1 = 33732 c.sub.1 = 67 Second floor m.sub.2 = 5897
k.sub.2 = 29093 c.sub.2 = 58 Third floor m.sub.3 = 5897 k.sub.3 =
28621 c.sub.3 = 57 Fourth floor m.sub.4 = 5897 k.sub.4 = 24954
c.sub.4 = 50 Fifth floor m.sub.5 = 5897 k.sub.5 = 19059 c.sub.5 =
38
[0054] In addition, the lead rubber bearing was designed to have a
yield force of 14.38 kN. A hysteresis restoring force f.sub.LRB and
a non-dimensional hysteresis parameter z to be used in the
numerical analysis are obtained by the following formulae.
f.sub.LRB=Q.sub.pb+k.sub.bx.sub.b+c.sub.b{dot over (x)}.sub.b
=-.gamma.|{dot over (u)}.sub.b|z|z|.sup.n-1-.beta.{dot over
(u)}.sub.b|z|.sup.n+A{dot over (u)}.sub.b
[0055] Here, Q.sub.pb is a yield load of lead, and is obtained by
Q.sub.pb=(1-K.sub.yield/K.sub.initial)Q.sub.y. Q.sub.y is 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 .beta., .gamma., 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-US-00002 TABLE 2 Parameter Value Parameter Value Qpb
14.48(kN) .gamma. 38.37 Qy 18.14(kN) A 76.74
K.sub.yield/K.sub.initial 6 n 1 .beta. -38.37
[0056] 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 = .intg. 0 .infin. ( z T Qz + F T RF ) t ##EQU00003##
[0057] The Q value and the R value were obtained through a trial
and error method and used as follows.
R = 1 ( 22 kN ) 2 = 1 ( 22000 ) 2 , ##EQU00004## Q = diag ( q
drifts ' I 0 0 q accels ' I ) ##EQU00004.2## Here , q drifts ' =
33.1 , q accels ' = 99.3 ##EQU00004.3##
[0058] 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.
[0059] 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.
[0060] 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-US-00003 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
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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-US-00004 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-US-00005 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.
[0069] 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 10a may be configured as shown in FIG. 7. That is,
the seismic control bearing device 10a 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
* * * * *