High damping structure

A high damping device combined with the frame of a building to protect the building from seismic shock. For seismic vibration up to a predetermined level corresponding to the permissible strength of the high damping device, a damping coefficient c of the high damping device is set so as to be c.sub.3 =c=c.sub.1 with respect to a damping coefficient c.sub.3 for giving the maximum value of a damping factor h.sub.3 corresponding to a tertiary mode of vibration of the structure and a damping coefficient c.sub.1 for giving the maximum value of a damping factor h.sub.1 corresponding to a primary mode of vibration. The maximum load on the high damping device is predetermined and means are provided to prevent the high damping device from being damaged in the event that the predetermined maximum load is exceeded. The inventive combination permits the stiffness factor of the building to be reduced from a factor of 1.0 down to a factor as low as 0.3, with a proportionate reduction in steel frame mass.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The field of invention comprises devices for damping vibrations of 
structures caused by seismic shock or the like. 
2. Description of Related Art 
A variety of active and passive seismic response control systems are known, 
including variable stiffness devices, to provide for the safety of 
structures. For instance, a variable stiffness earthquake-resisting 
mechanism may be integrated in a column-and-beam type frame structure in 
the form of an adjustable brace in which the rigidity of the variable 
stiffness mechanism, or the means of connection between the frame and the 
variable stiffness mechanism, functions to analyze seismic vibrational 
forces and to provide damping to offset these forces. 
Prior art active seismic response control systems attempt to deal with 
seismic vibrations by actively shifting the natural frequency of the 
structure against the predominant period of a seismic vibration. However, 
seismic motion is an irregular vibration which does not have a clear 
predominant period, and in some instances, the predominant period is 
plural. Furthermore, in the case of prior art active seismic response 
control systems, various sensors as well as a controlling computer are 
used. To safeguard against the possibility of unforeseen events, a variety 
of safety maintenance mechanisms are necessary, the control of which 
becomes complicated. These safety mechanisms are not only costly, but 
require valuable start-up time to become effective. During this start-up 
period, the structure is either unprotected or not fully protected. 
For instance, Kobori et al. U.S. Pat. No. 4,890,430 discloses an active 
damper which is computer controlled to vary the natural resonance of an 
entire building by actively varying the rigidity of selected structural 
members. Kobori. et al. U.S. Pat. No. 5,022,201 is an active seismic 
damper comprising a mass damper mounted on the top of a building. The 
damper is actively vibrated by an actuator connecting the mass to the 
building. Ishii et al. U.S. Pat. No. 5,025,599 discloses a combination 
active and passive damping device wherein a mass damper is rendered 
actively vibratable by a hydraulic actuator. In the event of a power 
failure, the device is converted to a passive damper wherein the mass is 
passively vibratable by coiled springs between the mass and the building 
which are excited solely by the energy of seismic vibration. 
SUMMARY OF THE INVENTION 
As used in this specification, the following definitions shall apply: 
1. Active damper shall mean a seismic vibration damping device which, in 
order to function, requires an actuator energized by means other than the 
energy of seismic vibration. 
2. Passive damper shall mean a seismic damping device which functions 
without an actuator and is energized solely by the energy of seismic 
vibration. 
3. Actuator shall mean a mechanical, electro-mechanical, electrical, and/or 
electronic means for energizing an active damper. 
4. Control force shall mean the force applied by a seismic vibration 
damping device to a structure to damp seismic vibrations in the structure. 
5. Fail safe means shall mean a device to automatically deactivate a 
seismic vibration damper to protect the damper from damage due to overload 
or malfunction. 
6. Column and beam shall mean state of the art construction materials used 
to form the vertical and horizontal frame portions of a structure. 
The basic concept of the invention is to use a rigid frame structure with a 
stiffness factor of approximately one-half of the stiffness and strength 
factor of a frame required in a normal design. To compensate for the 
reduced rigidity of the frame structure, the damping devices, in 
combination with earthquake-resisting elements, such as braces, are 
secured to the column-and-beam frame of the structure. Maximum damping 
capacity is obtained for the structure, and the response of the structure 
is minimized by preliminarily setting the damping coefficient of the 
inventive high damping device at a proper value. Although a structure 
having one-half of the frame stiffness of a prior art structure is an 
example of a structure suitable for protection by the inventive high 
damping device, the invention provides effective protection for 
column-and-beam frames having a stiffness and strength factor 
substantially within a range of 0.3 through 1.0 of the stiffness of a 
prior art structure designed and equipped with prior art 
earthquake-resisting devices. In the case where the structure stiffness 
factor exceeds 1.0, seismic response reduction becomes progressively less 
effective. On the other hand, where the strength of the structure is less 
than 0.3, effective damping becomes substantially impossible because of 
the shearing forces to which the column-and-beam frame is subjected. 
According to the present invention, earthquake-resisting braces are 
provided within a predetermined column-and-beam type frame of a structure. 
Either the column-and-beam frame and the braces are interconnected with 
the inventive high damping devices, or only the braces are interconnected 
by the inventive high damping devices, which are capable of giving a 
damping coefficient c within a predetermined range, including a damping 
coefficient for minimizing the response of the structure to an earthquake. 
With reference to the damping coefficient c of the high damping device, a 
damping factor of each vibration mode of the structure is obtained by the 
following formula (1): 
EQU H.sub.1 =-Re (.lambda.i)/.vertline..lambda.i.vertline. (1) 
wherein 
.lambda.i:an i-th complex natural value 
hi:an i-th damping factor, and 
Re(.lambda.i):a real number part of the i-th complex natural value. 
The damping coefficient c of the high damping device is taken as being set 
in the neighborhood of such damping coefficients c.sub.1, c.sub.2 and 
c.sub.3 which give the maximum values of damping factors h.sub.1, h.sub.2 
and h.sub.3 corresponding to the primary through tertiary vibration modes, 
respectively. 
With reference to the damping capacity of the structure, a most 
advantageous condition can be obtained by setting the coefficient c within 
the range: 
EQU c.sub.3 .ltoreq.c.ltoreq.c.sub.1 
The damping coefficient c of the high damping device is preliminarily set 
in the neighborhood of the damping coefficients c.sub.1, c.sub.2 or 
c.sub.3 (e.g., 25 cm/sec) which provide the maximum values of the damping 
factors h.sub.1, h.sub.2 and h.sub.3 corresponding to the primary through 
tertiary vibration modes as described above, and the damping coefficient 
of the high damping device is preset for the seismic motion at a 
predetermined vibration level. 
Seismic response control can also be accomplished by defining the damping 
coefficient c as c.sub.a =F.sub.a /V.sub.L' wherein F.sub.a is the 
permissible strength of the high damping device and V.sub.L is a response 
velocity of the high damping device due to an earthquake at a 
predetermined vibration level. The damping coefficient c of the high 
damping device may also be expressed as c.sub.x =F.sub.a /V.sub.x wherein 
F.sub.a is the permissible strength of the high damping device and V.sub.x 
is a response velocity of the high damping device due to an earthquake) 
for an earthquake at the preceding predetermined vibrational level. 
Assuming that the permissible strength F.sub.a of a single high damping 
device is 100 tons, maximum damping is provided for the structure while 
keeping the damping coefficient c at a predetermined constant value of 25 
tons per cm/sec responsive to seismic vibration up to a level of 25 
cm/sec, for an earthquake having the maximum speed standardized to 25 
cm/sec. The load is kept at approximately 100 tons of the permissible 
strength by gradually decreasing the preset damping coefficient from 25 
cm/sec. Within these parameters, damping can be provided for the structure 
within the capacity of the device while at the same time protecting the 
device from damage should the seismic vibrations exceed the capacity of 
the device. It is desirable that the damping coefficient c.sub.a within a 
predetermined vibrational level be within the range of c.sub.3 through 
c.sub.1. When the damping coefficient c.sub.a falls below this range, the 
damping effectiveness decreases. Also, when the damping coefficient 
c.sub.a exceeds this range, it becomes difficult to design a high damping 
device having the capacity to damp such high energy vibration loads. 
OBJECTS OF THE INVENTION 
It is among the objects of this invention to provide a passive seismic 
response control mechanism which does not need as part of the control 
system a computer program or the like; to permit a structure to have a 
high damping capacity by properly connecting an earthquake vibration 
resisting element, such as a brace, to a high damping device, which are 
then interconnected within a column-and-beam type frame structure; to 
reduce the vibrations of a structure due to external disturbances such as 
earthquake, wind, or the like; and to provide safe living space within the 
structure during a seismic disturbance.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
Referring first to FIG. 1, therein is shown a structure 1 employing the 
inventive high damping device 10, having a column-and-beam type frame 
which requires approximately only one-half of the columns 2 required of a 
conventional prior art structure, such as shown in FIG. 2, having the same 
number of stories. Inverted V-type braces 4, functioning as 
earthquake-resisting elements, and high damping devices 10 are locally 
installed at each floor level 3 to absorb vibrational energy impacting the 
structure. 
FIG. 3 schematically shows a single story model of the inventive high 
damping device, in which c is the damping coefficient of the device, 
K.sub.F is the stiffness of the column-and-beam frame, and K.sub.V is the 
stiffness of the brace. With this model, the natural value of a 
multi-story building can be obtained, and a damping factor for each mode 
of the structure can be calculated by formula (1), set forth above. 
The graph of FIG. 4 shows the relation between the damping factor h(%) of 
the frame's natural period and the damping coefficient c (tons/cm/sec) of 
the inventive high damping device 10 for each floor level of the structure 
with respect to primary through tertiary coefficient modes and their 
corresponding damping factors. If the damping coefficient c of the 
inventive high damping device 10 is set within the range a where each 
damping factor h.sub.1, h.sub.2 or h.sub.3 falls within the range of 10 
through 40%, a sufficient response reduction effect to seismic vibration 
can be obtained. Within this range a, the difference between the peak of 
the tertiary damping factor h.sub.3 and the peak of the primary damping 
factor h.sub.1 is significant, since it is advantageous to obtain both a 
damping coefficient c.sub.3 which obtains the maximum value of the damping 
factor h.sub.3 for the tertiary mode and a damping coefficient c.sub.1 
which obtains the maximum value of the damping factor h.sub.1 for the 
primary mode, and to set the damping coefficient c of the high damping 
device as c.sub.3 .ltoreq.c.ltoreq.c.sub.1. 
If the damping coefficient c is less than c.sub.3, the deformation of the 
frame rapidly increases. On the other hand, if the damping coefficient c 
is more than c.sub.1, there is not much difference in the vibration 
control effect, although the strength required for the high damping device 
increases. 
The graph of FIG. 5 illustrates the response reduction effect observed on 
the basis of a seismic response spectrum. By approximately halving the 
column-and-beam frame natural period (T.sub.1) of a prior art structure, 
the natural period (T.sub.2) is extended and the spectrum itself is 
lowered. At the same time, since the damping effect increases by 
approximately 2% up to 10 through 40%, the response spectrum is further 
lowered and the natural period is slightly shortened, as shown at T.sub.3. 
At this time, the increase of the structural deformation, which normally 
becomes a problem, can be controlled because the damping effect increases. 
With reference to the foregoing discussion of FIGS. 4 and 5, the 
permissible strength of the high damping device should be taken into 
consideration as well. Thus, since the load applied on the inventive high 
damping device is roughly proportional to the scale and velocity of the 
seismic vibrations when the damping coefficient c is constant, when the 
damping coefficient c is decreased responsive to an earthquake exceeding a 
predetermined level (e.g., 25 cm/sec), the applied load will decrease to a 
level commensurate with the designed strength of the inventive high 
damping device. 
FIGS. 6 and 7 are graphs showing effects of load on an inventive high 
damping device. FIG. 6 shows the relationship between load and 
displacement against a sine wave expressed as F=c.sub.V, wherein F is a 
load applied on the inventive device, c is the damping coefficient 
(tons/cm/sec) of the device, and V is the velocity (cm/sec) of the device 
in response to an earthquake. Displacement of the inventive device in 
response to a level 25 cm/sec earthquake is indicated by the 
.delta..sub.25 arrow. Displacement of the inventive device in response to 
a level 50 kine earthquake is indicated by the .delta..sub.50 arrow. FIG. 
7 shows the relationship between load and velocity, and both figures 
indicate an upper load limit of 100 tons. It is found that the damping 
coefficient c of the inventive device decreases from a velocity of 
V.sub.25 or a displacement of .delta..sub.25 in response to an earthquake 
at a level of 25 cm/sec. 
By way of example, assume a twenty-four story building, having a rigid 
steel frame structure 98.1 m in height, 3.90 m in typical floor height, 
and 1269 m.sup.2 in typical floor area, and assume that the maximum 
velocity amplitude of the input seismic motion is at a level of 50 cm/sec. 
Also assume that four inventive high damping devices are required on every 
floor of the building in order to have the required strength in the event 
of seismic loads in the order of 200 tons. The damping coefficient c is 
set at 25 tons/cm/sec in order to limit the maximum load to under 100 tons 
applied to each inventive high damping device, and the damping coefficient 
c is decreased against earthquakes exceeding the 25 cm/sec level so as to 
avoid harmful increase of the load on each of the inventive devices per 
se. Thus, in the inventive high damping device the relationship between a 
load F and a velocity V produced on the high damping device approaches 
linearity. 
As an embodiment of the inventive high damping device 10, FIG. 8 shows its 
basic structure, wherein a piston 12, with piston rods 12a and 12b, is 
incorporated within a cylinder 11. Pressure regulating valves 17a and 17b 
provide two-way flow paths through the piston 12 to enable oil to flow 
freely between hydraulic chambers 14a and 14b, depending on which 
hydraulic chamber is under the greater positive pressure. 
In order to protect the inventive device against overload (e.g., in excess 
of the predetermined level), relief valves 27a and 27b are provided in 
piston 12. When a pressure in excess of the designed load is applied, 
either relief valve 27a or 27b opens to release the pressure. In 
installations in which overload cannot occur, the relief valves 27a and 
27b may be eliminated. 
FIG. 9 shows the arrangement of pressure regulating valves 17a and 17b and 
relief valves 27a and 27b, which are uniformly circumferentially arrayed 
to form passageways through piston 12. 
FIG. 10 diagrammatically shows an embodiment of the damping device 10 in 
which the piston rod 12a projects from the cylinder 11 only in one 
direction, and fastening rings 15 and 16 are provided for connecting the 
inventive high damping device to portions of a frame, such as shown in 
FIGS. 15 through 22. The high damping device of FIG. 10 includes an oil 
accumulator 18 in combination with check valves 20a and 20b so that the 
damper will have an adequate supply of oil at all times. 
The embodiment of FIG. 11 shows in section pressure regulating valves 17a 
and 17b which are provided within the piston 12 for the purpose of 
preventing oil from leaking to the exterior of the damper. The pressure 
regulating valves 17a and 17b are provided with conical poppet valves to 
provide damping independent of temperature. See also FIG. 12. For 
durability and reliability, multi-stage metal seals 29a are used to seal 
the piston 12 for sliding contact with cylinder 11. Two-stage metal seals 
29b are also used as fixed seals. In addition, seals 29c, made of a 
fluorocarbon resin, are provided in two stages for the rod portion, and 
the seal 29c on the external side is replaceable as a cartridge. With this 
combination of sliding and fixed seals, a high damping coefficient becomes 
possible by minimizing the potential for high pressure oil leaks in the 
system. A three-directional rotatable clevis may be used for connecting 
the fitting ring 15 to a frame member. 
Referring to FIG. 13, therein is shown, in an open-pressure setting, spring 
28 in relief valve 27. When the seismic vibration of an earthquake exceeds 
a predetermined level of energy, resulting in pressure at an inflow 
portion of the total surface of a valve reaching a pressure higher than a 
designed pressure, the relief valve 27 has a pressure pad 27a for opening 
the valve against the resistance of the spring 28 to release the pressure. 
FIG. 14 shows by-pass line 19 and the accumulator 18 which are mounted on 
the surface of the casing 11 of the high damping device 10. A check valve 
20a, for preventing an oil flow toward the side of the hydraulic chamber 
14a, is provided between the hydraulic chamber 14a and the accumulator 18, 
and a check valve 20b for preventing an oil flow toward the side of the 
hydraulic chamber 14b is provided between a hydraulic chamber 14b and the 
accumulator. Moreover, check valves 20a and 20b are attached to orifices 
21a and 21b, respectively, passing through each of the check valves (in 
parallel with each other as shown in FIG. 10) to linearize the damping 
characteristics of the high damping device 10 and to relieve a pressure 
build-up within either hydraulic chamber 14a or 14b. 
FIGS. 15 through 22 show installation embodiments of the high damping 
device 10 within a column-and-beam type frame. 
In the embodiment of FIG. 15, the high damping device 10 is interposed 
between a column-and-beam frame 31 and an inverted V-type brace 35, which 
functions as the earthquake-resisting element. 
The embodiment shown in FIG. 16 employs U-shaped braces 41 which act as 
earthquake-resisting elements. The high damping device 10 is secured 
between the U-shaped braces 41, which are secured to beams 34 and extend 
vertically therefrom. 
In the embodiment of FIG. 17, the high damping device 10 is interposed 
between the upper beam 34 and an earthquake-resisting wall brace 42. 
In the embodiment shown in FIG. 18, the high damping device 10 is secured 
between the lower beam 34 and the base B of a structure mounted on base 
isolation pads 43. The earthquake-resisting element is an inverted V-type 
brace 35, similar to the brace shown in FIG. 15. 
In the embodiment of FIG. 19, an earthquake-resisting X-type brace 44 is 
installed within the column-and-beam frame 31. The high damping device 10 
is horizontally secured at the center of the brace. 
In an embodiment similar to that of FIG. 19, the embodiment shown in FIG. 
20 comprises the high damping device 10 vertically secured to an X-type 
brace 45. 
In an embodiment similar to that shown in FIG. 17, the embodiment shown in 
FIG. 21 discloses the high damping device 10 interposed between the beam 
34 and an earthquake-resisting wall brace 46, wherein the high damping 
device 10 is secured to the vertical edge of the wall brace 46 and over a 
doorway 47. 
In the embodiment shown in FIG. 22, the high damping device 10 is 
horizontally interposed at the center of an X-type brace 48 which extends 
over three stories of a structure, from floor 49A to floor 49D, with the 
extremities of the X-type brace secured only to floors 49A and 49D. 
POSSIBILITY OF INDUSTRIAL UTILIZATION 
The following advantages will be obtained by applying a high damping device 
of the present invention to buildings which are at risk to the ravages of 
earthquakes and high winds. 
1. Since the number of columns of a column-and-beam structure can be 
reduced by approximately 50%, not only is the saving in structural steel 
considerable, but the additional unobstructed floor space between columns 
considerably increases the floor planning possibilities. 
2. Since the response of the structure to earthquake shock and high winds 
is reduced, the safety of the occupants and of the structure is increased. 
3. Since the invention is a passive type damper mechanism, only fine tuning 
adjustments to the particular characteristics of the structure are 
required when installed. 
4. Since complicated active seismic control systems and attached facilities 
are not required, installation costs are low in comparison to the costs of 
active seismic response control mechanisms. 
5. The effective load applied to the inventive high damping device may be 
decreased by reducing the damping coefficient for seismic vibration to a 
predetermined safe level. 
6. The number of inventive damping devices to be installed on each floor of 
a building can be predetermined. 
7. Since the designed load limit of the inventive device cannot be 
exceeded, the cost of material and labor for related support structure can 
be reduced and a compact installation can be obtained. 
It will occur to those skilled in the art, upon reading the foregoing 
description of the preferred embodiments of the invention, taken in 
conjunction with a study of the drawings, that certain modifications may 
be made to the invention without departing from the intent or scope of the 
invention. It is intended, therefore, that the invention be construed and 
limited only by the appended claims.