U.S. patent application number 11/598262 was filed with the patent office on 2007-03-15 for buckling restrained braces and damping steel structures.
This patent application is currently assigned to Nippon Steel Corporation. Invention is credited to Hisami Hasegawa, Isao Kimura, Hiroshi Nakamura, Eiichiro Saeki, Toru Takeuchi, Atsushi Watanabe.
Application Number | 20070056225 11/598262 |
Document ID | / |
Family ID | 27475278 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070056225 |
Kind Code |
A1 |
Takeuchi; Toru ; et
al. |
March 15, 2007 |
Buckling restrained braces and damping steel structures
Abstract
The present invention relates to a buckling restrained brace
capable of absorbing vibration energy produced by an earthquake,
wind power and the like, in a building and a steel structure. The
buckling restrained brace of the present invention is accomplished
by a buckling restrained brace 1 wherein a steel-made center axial
member 3 is passed through a buckling-constraining concrete member
2 reinforced with a steel member 6, and an adhesion-preventive film
4 is provided to the interface between the steel-made center axial
member and buckling-constraining concrete 5, the
adhesion-preventive film showing a secant modulus in the thickness
direction of at least 0.1 N/mm.sup.2 between a point which shows a
compressive strain of 0% and a point which shows a compressive
strain of 50%, and up to 21,000 N/mm.sup.2 between a point which
shows a compressive strain of 50% and a point which shows a
compressive strain of 75%, and having a thickness d.sub.t in the
plate thickness direction of the steel-made center axial member and
a thickness d.sub.w in the plate width direction thereof from at
least 0.5 to 10% of the plate thickness t and from at least 0.5 to
10% of the plate width w, respectively, and by the application of
the buckling restrained brace to a damping steel structure.
Inventors: |
Takeuchi; Toru; (Tokyo,
JP) ; Nakamura; Hiroshi; (Tokyo, JP) ; Kimura;
Isao; (Tokyo, JP) ; Hasegawa; Hisami; (Tokyo,
JP) ; Saeki; Eiichiro; (Tokyo, JP) ; Watanabe;
Atsushi; (Tokyo, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Assignee: |
Nippon Steel Corporation
Tokyo
JP
|
Family ID: |
27475278 |
Appl. No.: |
11/598262 |
Filed: |
November 8, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10961007 |
Oct 7, 2004 |
|
|
|
11598262 |
Nov 8, 2006 |
|
|
|
09735252 |
Dec 12, 2000 |
6826874 |
|
|
10961007 |
Oct 7, 2004 |
|
|
|
09511207 |
Feb 23, 2000 |
|
|
|
09735252 |
Dec 12, 2000 |
|
|
|
Current U.S.
Class: |
52/167.1 |
Current CPC
Class: |
E04H 9/0237 20200501;
E04H 9/028 20130101; E04H 9/02 20130101 |
Class at
Publication: |
052/167.1 |
International
Class: |
E04H 9/02 20060101
E04H009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 1999 |
JP |
11-186384 |
Dec 8, 1999 |
JP |
11-349175 |
Jun 26, 2000 |
JP |
2000-191718 |
Claims
1. A buckling restrained brace (1) wherein a steel-made center
axial member (3) is passed through a buckling-constraining concrete
member (2) reinforced with a steel member (6), and an
adhesion-preventive film (4) is provided to the interface between
the steel-made center axial member (3) and buckling-constraining
concrete (5), the adhesion-preventive film (4) showing a secant
modulus in the thickness direction of at least 0.1 N/mm.sup.2
between a point which shows a compressive strain of 0% and a point
which shows a compressive strain of 50%, and up to 21,000
N/mm.sup.2 between a point which shows a compressive strain of 50%
and a point which shows a compressive strain of 75%, and having a
thickness (d.sub.t) in the plate thickness direction of the
steel-made center axial member (3) and a thickness (d.sub.w) in the
plate width direction thereof from at least 0.5 to 10% of the plate
thickness (t) and from at least 0.5 to 10% of the plate width (w),
respectively.
2. A buckling restrained brace according to claim 1, wherein the
steel-made center axial member (3) is a steel material showing a
0.2% proof stress or a yield point stress of up to 130
N/mm.sup.2.
3. A buckling restrained brace according to claim 1, wherein the
steel-made center axial member (3) is a steel material showing a
0.2% proof stress or a yield point stress of 130 to 245
N/mm.sup.2.
4. A buckling restrained brace according to claim 1, wherein the
steel-made center axial member (3) has a minimum cross-sectional
area in a central portion (21) in the longitudinal direction having
a restricted length ratio which is the ratio of the length of the
central portion (21) to the whole length, and the steel-made center
axial member has a cross-sectional area larger than the minimum
cross-sectional area of the central portion (21) in the
longitudinal direction, at both ends (22, 23) in the longitudinal
direction connectively provided to the central portion (21) in the
longitudinal direction.
5. A buckling restrained brace according to claim 4, wherein the
steel-made center axial member (3) shows an axial equivalent
stiffness of at least 1.5 times that of the steel-made center axial
member (3) in any one of claims 1 to 3 which have same-sectional
area from one end to the other end, passing through the central
portion (21) in the length direction of said member (3).
6. A buckling restrained brace according to claim 1, wherein each
of the cross-sectional areas (22-1, 23-1) at both ends (22, 23) in
the longitudinal direction of the steel-made center axial member
(3) which is obtained by subtracting a through hole-formed
deficient area of the corresponding through holes (26) for bolt
insertion passing is at least 1.2 times the cross-sectional area
(21-1) of the central portion (21) in the longitudinal direction of
the steel-made center axial member (3).
7. A buckling restrained brace according to claim 1, wherein the
steel member (6) is a reinforcing bar (6-1).
8. A buckling restrained brace according to claim 1, wherein a lid
(24) is fixed to at least one end of the buckling-constraining
concrete member (2).
9. A buckling restrained brace according to claim 1, wherein a slip
stopper (25) is provided to the center of the steel-made center
axial member (3).
10. A buckling restrained brace according to claim 1, wherein the
buckling restrained brace (1) having the steel-made center axial
member (3) which is provided with through holes ( 26) for bolt
insertion passing at both ends (22, 23), and steel-made connecting
plates (27) are friction jointed with high tension bolts by
clamping, while the friction face sides at both ends (22, 23) of
the steel-made center axial member (3) which are contacted with the
respective friction face sides of the steel-made connecting plates
(27) or the friction face sides of the steel-made connecting plates
(27) which are contacted with the respective friction face sides at
both ends (22, 23) of the steel-made center axial member are made
to have a higher surface hardness and a higher surface roughness
than the counterpart friction face sides.
11. A buckling restrained brace according to claim 1, wherein at
least one set comprising three layers which are formed from a
C-shaped cross-sectional inside steel plate (29), a visco-elastic
sheet (30) and a C-shaped cross-sectional outside steel plate (31)
is fastened to each of the sides of the buckling-constraining
concrete member (2) of the buckling restrained brace (1), one end
(32) of the C-shaped cross-sectional inside steel plate (29) is
fastened to one end (34) of the buckling restrained brace (1), and
the other end (33) of the C-shaped cross-sectional outside steel
plate (31) is fastened to the other end (35) of the buckling
restrained brace (1) in the direction opposite to the one end (32)
of the C-shaped cross-sectional outside steel plate (29).
12. A damping steel structure (38) wherein the buckling restrained
braces (1) according to claim 1 or 4 are placed in the damping
steel structure (38) which is formed with columns (36) and beams
(37) prepared from a steel material showing a yield point stress
higher than that of the steel-made center axial members (3) of the
buckling restrained braces (1), the buckling restrained braces (1)
showing both elastic and plastic behavior when the damping steel
structure (38) vibrates under vibration action, and the damping
steel structure (38) which is formed with the columns and the
beams, showing elastic behavior.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part application of
Ser. No. 09/511,207 filed on Feb. 23, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to buckling restrained braces
used in buildings and steel structures and capable of absorbing
vibration energy generated by an earthquake, wind power, etc.
[0004] 2. Description of the Related Art
[0005] Japanese Examined Utility Model (Kokoku) No. 4-19121
discloses a buckling-constraining brace member in which an
adhesion-preventive film is provided between a center axial member
and a concrete member. Japanese Unexamined Utility Model (Kokai)
No. 5-3402 discloses a buckling-constraining brace member wherein a
steel-made center axial member is passed through a steel-made
buckling-constraining member, and an adhesion-preventive film is
placed between the surface of the center axial member and the
buckling-constraining member. Japanese Unexamined Utility Model
(Kokai) No. 5-57110 discloses a damping brace member wherein both
ends of an intermediate member having a small cross section are
each connectively and integrally jointed to one end of a side
member having a large cross section, in series to form a steel-made
center axial member, and the axial member is fitted in a
constituent hollow buckling-constraining member. Japanese
Unexamined Utility Model (Kokai) No. 5-57111 discloses a damping
brace member having the same constitution as in Japanese Unexamined
Utility Model (Kokai) No. 5-57110 and excellent in damping
properties, durability and weatherability. Japanese Unexamined
Patent Publication (Kokai) No. 7-229204 discloses that the
stiffness and yield stress of a buckling-constraining brace member
can be arbitrarily determined, and that the stress flow of the
steel-made center axial member is improved. R. Tremblay et al.
reported experimental result relate to buckling-constraining
members in the 8th Canadian conference on Earthquake Engineering
(cf. Seismic Rehabilitation of a Four-stored Building with a
Stiffened Bracing System, published on, Jan. 19, 1999).
SUMMARY OF THE INVENTION
[0006] An adhesion-preventive film is provided between a
buckling-constraining concrete member reinforced with a steel
material and a steel-made center axial member for the purpose of
preventing the steel-made center axial member from adhering to the
concrete of the buckling-constraining concrete member. The
following problems, about the adhesion-preventive film, arise. When
the adhesion-preventive film is too thin, the film does not
tolerate the expansion in the plate thickness direction of the
steel-made center axial member caused by its axial deformation; on
the other hand, when the adhesion-preventive film is too thick, it
is incapable of constraining local buckling of the steel-made
center axial member. Moreover the adhesion-preventive film has
still other problems as mentioned below. When the stiffness in the
thickness direction of the adhesion-preventive film is too low, it
is incapable of maintaining a predetermined thickness due to the
concrete pressure during pouring concrete; moreover, when the
stiffness in the thickness direction thereof is too high, it cannot
absorb the expansion in the plate thickness direction of the
steel-made center axial member caused by the influence of Poisson's
ratio at the time of plasticization, namely, plastic deformation of
the steel-made center axial member.
[0007] When a plain steel (yield stress .sigma..sub.y=235
N/mm.sup.2) is used for the steel-made center axial member of a
buckling restrained brace, there arises a problem that the buckling
restrained brace cannot be made to function as a hysteresis damper
against an earthquake of a small magnitude because the steel-made
center axial member does not yield at the early stage against a
ground motion acceleration (80 to 100 gal) of the earthquake.
[0008] A steel-made center axial member of a buckling restrained
brace having the same cross-sectional area from one end of the
member, through the central portion, to the other end has the
following problem. When the steel-made center axial member is made
to function as a hysteresis damper, both ends as well as the
central portion of the member are plasticized (plastically
deformed) due to yielding, and consequently fracture at joints
between the buckling restrained brace and a steel structure
including a column and a beam takes place.
[0009] In the process of producing a buckling-constraining concrete
member of a buckling restrained brace reinforced with a steel
material, when the ends of the reinforcing steel material of a
buckling-constraining concrete member are open, there arise
problems as mentioned below. During pouring the concrete, the
concrete flows out before its solidification, and pouring concrete
becomes difficult; cracked concrete falls during the use of the
buckling restrained brace. Furthermore, an adhesion-preventive film
is placed between the buckling-constraining concrete member of the
buckling restrained brace reinforced with the steel material and
the steel-made center axial member for the purpose of preventing
mutual adhesion between the axial member and the concrete member.
Accordingly, the following problem arises. When the steel-made
center axial member is axially deformed due to vibration generated
by an earthquake or wind power, it is not definite in which of two
directions, a direction towards one end of the steel-made center
axial member and a direction towards the other end thereof, the
buckling-constraining concrete member is moved, and the concrete
member is deflected to one of the two ends when the concrete member
starts to be moved.
[0010] When the buckling restrained brace is to be mounted on a
damping steel structure, the buckling restrained brace is generally
jointed with high tensile bolts. In jointing the buckling
restrained brace, the following problem arises. When the axial
tension of the steel-made center axial member increases, the number
of bolts used significantly increases, and the buckling restrained
brace cannot be fixing jointed unless both of its ends are
extremely expanded. Moreover, the width of both ends of the
buckling restrained brace cannot be increased much because the
width is restricted by the widths of columns and beams of the
damping steel structure on which the buckling restrained brace is
to be mounted.
[0011] The buckling restrained brace has a problem that the
steel-made center axial member cannot be made to function as a
hysteresis damper for absorbing vibration energy of the
micro-vibration of an earthquake of very small magnitude, wind
power, etc., to which the steel-made center axial member does not
yield.
[0012] When the steel structure is shaken by an earthquake of a
large magnitude, part of the columns, beams and braces of the steel
structure are plasticized. Even when they are plasticized, the
steel structure does not collapse so long as they have a sufficient
capacity of plastic deformation and sufficient resistant to
fatigue. However, jointed portions and welded portions prepared by
field fabrication tend to decline in quality compared with those
prepared by factory production, and are sometimes fractured before
performing a sufficient plastic deformation function. When these
columns, beams and braces are plasticized, the steel structure is
deformed, and there arises a problem that the steel structure must
be repaired on a large scale if it is to be used after the
earthquake.
[0013] The problems mentioned above are solved by a buckling
restrained brace 1 according to the present invention wherein a
steel-made center axial member 3 is passed through a
buckling-constraining concrete member 2 reinforced with a steel
member 6, and an adhesion-preventive film 4 is provided to the
interface between the steel-made center axial member and
buckling-constraining concrete 5, the adhesion-preventive film
showing a secant modulus in the thickness direction of at least 0.1
N/mm.sup.2 between a point which shows a compressive strain of 0%
and a point which shows a compressive strain of 50%, and up to
21,000 N/mm.sup.2 between a point which shows a compressive strain
of 50% and a point which shows a compressive strain of 75%, and
having a thickness d.sub.t in the plate thickness direction of the
steel-made center axial member 3 and a thickness d.sub.w in the
plate width direction thereof from at least 0.5 to 10% of the plate
thickness t and from at least 0.5 to 10% of the plate width w,
respectively.
[0014] When considering pressure for placing concrete 5 in
manufacturing a buckling-restraining brace 1, a desirable minimum
thickness ratio of the adhesion-preventive film 4 and a steel-made
center axial member 3 is preferably in the range from not less than
1.2% to up to 10%.
[0015] Moreover, in the buckling restrained brace according to the
present invention, the steel-made center axial member 3 is a steel
material showing a 0.2% proof stress or a yield point stress of up
to 130 N/mm.sup.2.
[0016] Furthermore, in the buckling restrained brace according to
the present invention, the steel-made center axial member 3 is a
steel material showing a 0.2% proof stress or a yield point stress
of 130 to 245 N/mm.sup.2.
[0017] Still furthermore, in the buckling restrained brace
according to the present invention, the steel-made center axial
member 3 has a minimum cross-sectional area in a central portion 21
in the longitudinal direction having a restricted length ratio
which is the ratio of the length of the central portion to the
whole length, and the steel-made center axial member has a
cross-sectional area larger than the minimum cross-sectional area
of the central portion 21 in the longitudinal direction, at both
ends 22, 23 in the longitudinal direction connectively provided to
the central portion in the longitudinal direction.
[0018] Moreover, in the buckling restrained brace 1 having a
cross-sectional area of the central portion (21) as described in
the above, the steel-made center axial member (3) shows an axial
equivalent stiffness of at least 1.5 times that of the steel-made
center axial member (3) which has same-sectional area from one end
to the other end, passing through the central portion (21) in the
length direction of said member (3).
[0019] Furthermore, in the buckling restrained brace according to
the present invention, each of the cross-sectional areas 22-1, 23-1
at both ends 22, 23 in the longitudinal direction of the steel-made
center axial member 3 which is obtained by subtracting a through
hole-formed deficient area of the corresponding through holes for
bolt insertion passing is at least 1.2 times the cross-sectional
area 21-1 of the central portion 21 in the longitudinal direction
of the steel-made center axial member.
[0020] Moreover, in the buckling restrained brace 1 according to
the present invention, the steel member 6 is a reinforcing bar
6-1.
[0021] Still furthermore, in the buckling restrained brace 1
according to the present invention, a lid 24 is fixed to at least
one end of the buckling-constraining concrete member 2.
[0022] Moreover, in the buckling restrained brace according to the
present invention, a slip stopper 25 is provided to the center of
the steel-made center axial member 3.
[0023] Furthermore, in the buckling restrained brace 1 according to
the present invention, the buckling restrained brace 1 having the
steel-made center axial member 3 which is provided with through
holes 26 for bolt insertion at both ends 22, 23, and steel-made
connecting plates 27 are friction jointed with high tension bolts
by clamping, while the friction face sides at both ends 22, 23 of
the steel-made center axial member which are contacted with the
respective friction face sides of the steel-made connecting plates
27 or the friction face sides of the steel-made connecting plates
27 which are contacted with the respective friction face sides at
both ends 22, 23 of the steel-made center axial member are made to
have a higher surface hardness and a higher surface roughness than
the counterpart friction face sides.
[0024] Still furthermore, in the buckling restrained brace
according to the present invention, at least one set, comprising
three layers which are formed from a C-shaped cross-sectional
inside steel plate 29, a visco-elastic sheet 30 and a C-shaped
cross-sectional outside steel plate 31, is fastened to each of the
sides of the buckling-constraining concrete member 2 of the
buckling restrained brace 1; one end 32 of the C-shaped
cross-sectional inside steel plate 29 is fastened to one end 34 of
the buckling restrained brace 1; and the other end 33 of the
C-shaped cross-sectional outside steel plate 31 is fastened to the
other end 35 of the buckling restrained brace 1 in the direction
opposite to the one end 32 of the C-shaped cross-sectional outside
steel plate 29.
[0025] Still furthermore, the problems mentioned above are solved
by a damping steel structure 38 according to the present invention
wherein the above-mentioned buckling restrained braces 1 according
to the present invention are placed in the damping steel structure
38 which is formed with columns 36 and beams 37 prepared from a
steel material showing a yield point stress higher than that of the
steel-made center axial members 3 of the buckling restrained braces
1, the buckling restrained braces 1 showing both elastic and
plastic behavior when the damping steel structure 38 vibrates under
vibration action, and the steel structure 38 which is formed with
the columns and the beams, showing elastic behavior.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 (a) is a plane view of the buckling restrained brace
of the present invention.
[0027] FIG. 1 (b) is a cross section taken along the line X-X in
FIG. 1 (a).
[0028] FIG. 2 (a) is a fatigue curve of the buckling restrained
brace of the present invention.
[0029] FIG. 2 (b) is a schematic view of a strain
(.epsilon.)-stress (.sigma.) hysteresis loop in a fatigue cyclic
test.
[0030] FIG. 3 (a) shows the-relationship between a natural period T
and a story drift angle (rad) at a maximum response of a building
to which the buckling restrained brace of the present invention is
attached.
[0031] FIG. 3 (b) shows horizontal deformation and story drift
angles of the building.
[0032] FIG. 4 (a) is a plan view of a buckling restrained brace of
the present invention in which the cross-sectional area in the
central portion of the steel-made center axial member is
reduced.
[0033] FIG. 4 (b) is a cross section taken along the line X-X in
FIG. 4 (a).
[0034] FIG. 4 (c) is a cross section taken along the. line Y-Y in
FIG. 4 (a).
[0035] FIG. 5 (a) is a plan view of a buckling restrained brace of
the present invention in which the cross-sectional area in the
central-portion of the steel-made center axial member is
reduced.
[0036] FIG. 5 (b) is a cross section taken along the line X-X in
FIG. 5 (a).
[0037] FIG. 5 (c) is a cross section taken along the line Y-Y in
FIG. 5 (a).
[0038] FIG. 6 (a) is a schematic view of a damping steel structure
in which buckling restrained braces are placed in a steel structure
having columns and beams.
[0039] FIG. 6 (b) is an enlarged view of the portion indicated by Y
in FIG. 6 (a).
[0040] FIG. 6 (c) is a plan view of a buckling restrained brace of
the present invention in which the cross-sectional area of the
center portion of the steel-made center axial member is
reduced.
[0041] FIG. 7 (a) is a plan view of a buckling restrained brace of
the present invention in which the cross-sectional area in the
central portion of the steel-made center axial member is
reduced.
[0042] FIG. 7 (b) is a cross section taken along the line X-X in
FIG. 7 (a).
[0043] FIG. 7 (c) is a cross section taken along the line Y-Y in
FIG. 7 (a).
[0044] FIG. 8 (a) is a plan view of a buckling restrained brace of
the present invention in which the cross-sectional area in the
central portion of the steel-made center axial member is
reduced.
[0045] FIG. 8 (b) is a cross section taken along the line X-X in
FIG. 8 (a).
[0046] FIG. 8 (c) is a cross section taken along the line Y-Y in
FIG. 8 (a).
[0047] FIG. 9 shows a stress-strain curve of a steel used as a
steel material of the steel-made center axial member of a buckling
restrained brace of the present invention.
[0048] FIG. 10 (a) is a plain view of a buckling restrained brace
which is used as a reinforcing bar for a steel member of a
buckling-constraining concrete member.
[0049] FIG. 10 (b) is cross section taken along the x-x in FIG. 10
(a).
[0050] FIG. 11 (a) is a plain view of a buckling restrained brace
which is used as a reinforcing bar for a steel member of a
buckling-constraining concrete member.
[0051] FIG. 11 (b) is cross section taken along the x-x in FIG. 11
(a).
[0052] FIG. 12 (a) is a plan view of a buckling restrained brace of
the present invention in which a lid is provided to one end of the
buckling-constraining concrete member.
[0053] FIG. 12 (b) is a cross section taken along the line X-X in
FIG. 12 (a).
[0054] FIG. 13 (a) is a plan view of a buckling restrained brace of
the present invention in which a lid is provided to one end of the
buckling-constraining concrete member.
[0055] FIG. 13 (b) is a cross section taken along the line X-X in
FIG. 13 (a).
[0056] FIG. 14 (a) is a plan view of a buckling restrained brace of
the present invention in which a slip stopper is provided to the
central portion of the steel-made center axial member.
[0057] FIG. 14 (b) is a cross section taken along the line X-X in
FIG. 14 (a).
[0058] FIG. 15 (a) is a plan view of a buckling restrained brace of
the present invention in which a slip stopper is provided to the
central portion of the steel-made center axial member.
[0059] FIG. 15 (b) is a cross section taken along the line X-X in
FIG. 15 (a).
[0060] FIG. 16 (a) is a plan view of a buckling restrained brace of
the present invention in which through holes for bolt insertion are
provided at both ends of the steel-made center axial member.
[0061] FIG. 16 (b) is a cross section taken along the line X-X in
FIG. 16 (a).
[0062] FIG. 17 (a) is a plan view of a buckling restrained brace of
the present invention in which through holes for bolt insertion are
provided at both ends of the steel-made center axial member.
[0063] FIG. 17 (b) is a cross section taken along the line X-X in
FIG. 17 (a).
[0064] FIG. 18 (a) is a plan view of a buckling restrained brace of
the present invention capable of coping with micro-vibration.
[0065] FIG. 18 (b) is a cross section taken along the line X-X in
FIG. 18 (a).
[0066] FIG. 19 (a) is a schematic view of a damping steel structure
in which buckling restrained braces are placed in a steel structure
having columns and beams.
[0067] FIG. 19 (b) is an enlarged view of the portion indicated by
Y in FIG. 19 (a).
[0068] FIGS. 20 (a) shows an analytical model for nonlinear
analyzing a buckling restrained brace.
[0069] FIG. 20 (b) shows an analytical model for nonlinear
analyzing a buckling restrained brace.
[0070] FIG. 20 (c) is a schematic view of a steel center axial
member.
[0071] FIG. 21 (a) shows the relationship between an axial force
and a displacement in the axial direction of a buckling restrained
brace and shows the relationship when the adhesion-preventive film
ratio d.sub.t/t is 1.4%.
[0072] FIG. 21 (b) shows the relationship when the
adhesion-preventive film ratio d.sub.t/t is 11.1%.
[0073] FIG. 22 (a) shows the shape of protrusions on a friction
joint face.
[0074] FIG. 22 (b) shows an enlarged view of a protrusion.
[0075] FIG. 23 (a) shows the shape of protrusions on a friction
joint face.
[0076] FIG. 23 (b) shows an enlarged view of a protrusion.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0077] The present inventors have elucidated that, when a building
shaken by an earthquake of a large magnitude shows, for example,
story drift angle of 1/100 (refer to FIGS. 2 (a) and 2 (b)) and the
estimated maximum axial strain of the steel-made center axial
member is .epsilon..sub.1=1%
(.epsilon..sub.1=.DELTA..epsilon..sub.a/2), the steel-made center
axial member is permitted to show axial plastic deformation and is
prevented from being locally buckled by determining the ratio of a
thickness of the adhesion-preventive film to a plate thickness of
the steel-made center axial member, namely, the adhesion-preventive
film ratio to be at least 0.5%, and have further determined that
the adhesion-preventive film ratio must be up to 10% for the
purpose of constraining local buckling thereof.
[0078] The adhesion-preventive film ratio can be obtained by the
following procedure. The minimum value of the adhesion-preventive
film ratio is obtained from the condition under which the
steel-made center axial member is not contacted with the
buckling-constraining concrete member surrounding the periphery
thereof when the steel-made center axial member shows Poisson's
ratio-based deformation in the plate thickness direction caused by
its deformation in the axial direction. For a buckling restrained
brace 1 shown in FIG. 1 (a) and FIG. 1(b), when the axial strain
.epsilon..sub.1 of a steel-made center axial member 3 is 1.0% and
the Poisson's ratio is 0.5 during plastic deformation, the strain
.epsilon..sub.z in the plate thickness direction in the plastic
deformation portion of the steel-made center axial member 3 can be
obtained by the formula
.epsilon..sub.z=.nu..epsilon..sub.1=0.5.times.1.0%=0.5% (1)
[0079] Accordingly, an approximate minimum ratio of a film
thickness d.sub.t of an adhesion-preventive film 4 to a plate
thickness t of the steel-made center axial member should be given
by the formula d.sub.t/t=s.epsilon..sub.z/2=2.times.0.5%/2=0.5%
wherein s is a safety factor which is assumed to be 2.
[0080] When placing the concrete 5 of a buckling-constraining
member 2, it is considered that the pressure on the concrete 5 is
applied to an adhesion-preventive film 4 and this film is pressed
by the pressure in the thickness direction of the film. Therefore,
before placing the concrete 5, a preferable minimum thickness ratio
d.sub.t(min)/t of the adhesion-preventive film 4 and a steel-made
center axial member 3 must be at least about 1.2% of a plate
thickness t (or width w) of the steel-made center axial member.
This preferable minimum thickness ratio d.sub.t(min)/t before
placing the concrete 5 can be obtained from following equation (A).
The following equation (A) is based on the condition that, during
placing the concrete, compressive strain .epsilon..sub.z in the
thickness direction of the adhesion-preventive film is estimated to
be about 50%, and that, after placed the concrete, the
adhesion-preventive film is maintained at the thickness after it is
compressed by the strain .epsilon..sub.z. When, after placed the
concrete, the preferable thickness ratio d.sub.t( min)/t is defined
to be not less than 0.5%, this preferable minimum thickness ratio
d.sub.t(min)/t is d.sub.t/t={[d.sub.t(min)-(.mu.V)]/t}100=0.5%
(2)
[0081] Wherein d.sub.t(min) is the preferable minimum thickness of
adhesion-preventive film, t is the plate thickness of the
steel-made center axial member, V is a compressive deformed value
of the film after the concrete 5 is placed in the reinforcing steel
member 6, and .mu. is an additional safety factor for
deformation.
[0082] When at least V=0.5 d.sub.t(min) and .mu.=1.2, therefore,
{[d.sub.t(min)-(1.2.times.0.5d.sub.t(min))]/t}100=0.5%
(0.4d.sub.t(min)/t).times.100=0.5%
(d.sub.t(min)/t).times.100=1.25%
[0083] Thus, before placing the concrete 5, the minimum thickness
ratio d.sub.t(min)/t of the adhesion-preventive film 4 and a
steel-made center axial member 3 is preferably at least about 1.2%
of a plate thickness t (or width w) of the steel center axial
member.
[0084] On the other hand, the maximum value of the
adhesion-preventive film ratio can be obtained from the conditions
under which the local buckling of the steel-made center axial
member does not exert adverse effects on the relationship between a
load and a deformation and the resistance to fatigue of the
buckling restrained brace. Nonlinear analysis carried out on an
analysis model shown in FIGS. 20 (a), 20 (b) and 20 (c), and FIGS.
21 (a) and 21 (b) shows the results of analyzing the relationship
between a load and a deformation when the adhesion-preventive film
ratio d.sub.t/t is 1.4% or 11.1%. The buckling restrained brace
shows stabilized behavior in FIG. 21 (a), whereas it shows, in FIG.
21 (b), phenomena of a rapid decrease in the load in the course of
increasing the displacement, that is, it shows unstabilized
behavior. The unstabilized behavior is caused by local buckling of
the steel-made center axial member within the buckling-constraining
concrete member due to an excessive thickness of the
adhesion-preventive film. In order to prevent local buckling of the
steel-made center axial member 3, the adhesion-preventive film
ratio should be up to 10%.
[0085] That is, the film thickness in the adhesion-preventive film
ratio should be from at least 0.5 to 10% of the plate thickness of
the steel-made center axial member.
[0086] Next, the secant modulus of the adhesion-preventive film 4
is defined for two reasons. A first reason will be explained
below.
[0087] (1) The secant modulus is defined because the thickness
required of the adhesion-preventive film can be sufficiently
ensured after the buckling-constraining concrete member of a
buckling restrained brace is prepared by pouring concrete.
[0088] During pouring concrete, the adhesion-preventive film is
required to have such a rigidity, at the lowest point of the
buckling restrained brace where the concrete pressure is highest,
that the strain .epsilon..sub.z in the thickness direction is up to
50%. Consequently, the thickness of the adhesion-preventive film
becomes half of the initial thickness at the lowest point of
pouring concrete. However, the decrease is taken into consideration
by setting the safety factor s at 2 in the calculation of a minimum
value of the film, and a sufficient thickness of the
adhesion-preventive film as a whole can be ensured. The rigidity
(secant modulus) of the adhesion-preventive film is obtained by the
following procedure. The pouring pressure p of the concrete of the
buckling-constraining concrete member of the buckling restrained
brace is obtained by the formula p=wh=2.4.times.2=0.48
tf/m.sup.2=0.48 kgf/cm.sup.2 (3) wherein w is a unit volume weight
of the concrete (which is assumed to be 2.4 tf/m.sup.3), and h is a
pouring height of the concrete (which is assumed to be 2 m). The
rigidity of the film at the time when the strain .epsilon..sub.z in
the thickness direction is 50% is obtained by the formula
E.sub.min=p/.epsilon..sub.z=0.48/0.5.apprxeq.1.0 kgf/cm.sup.2 (4)
Therefore, the secant modulus in the thickness direction of the
adhesion-preventive film between the highest concrete pouring point
where the compressive strain (strain .epsilon..sub.z in the
thickness direction) is 0% and the lowest concrete pouring point
where the compressive strain is 50% is required to be at least 1.0
kgf/cm.sup.2 (0.1 N/mm.sup.2) .
[0089] A second reason for defining the secant modulus of the
adhesion-preventive film is explained below.
[0090] (2) The secant modulus is defined because the
adhesion-preventive film thus defined is capable of sufficiently
absorbing the-expansion of the steel-made center axial member of
the buckling restrained brace in the out-of-plane direction without
buckling when the steel-made center axial member is plastically
deformed.
[0091] The strain .epsilon..sub.z in the thickness direction of the
adhesion-preventive film at the lowest concrete pouring point is
50%, and the maximum strain .epsilon..sub.z in the thickness
direction thereof estimated from the decline of the building at the
time of an earthquake is defined to be 75%. Moreover, in general,
when the steel-made center axial member is plastically deformed by
vibration generated by an earthquake or the like, the axial member
is buckled if it is compression deformed, whereas the axial member
is not buckled if it is tensile deformed. Therefore, between a
point where the strain .epsilon..sub.z (compressive deformation
alone being considered) in the thickness direction is 50% and a
point where .epsilon..sub.z is 75%, the adhesion-preventive film is
required to have a rigidity of such a degree that the film can
absorb the expansion of the steel-made center axial member in the
out-of-plane direction to prevent the axial member from being
buckled when the axial member is plastically deformed. The
adhesion-preventive film is required to have a secant modulus of up
to the elastic coefficient of the buckling-constraining concrete
member. That is, the secant modulus E.sub.max of the
adhesion-preventive film is determined to be up to
2.1.times.10.sup.5 kgf/cm.sup.2 (21,000 N/mm.sup.2) between a point
where the strain .epsilon..sub.z in the thickness direction is 50%
and a point where .epsilon..sub.z is 75%.
[0092] Next, in order to make the steel-made center axial member of
a buckling restrained brace function as a hysteresis damper against
an earthquake of a small magnitude, a steel material having a 0.2%
proof stress or a yield point of up to 130 N/mm.sup.2 is used
therefore. As a result, even when a small earthquake showing a
ground motion acceleration of 80 to 100 gal happens, the steel-made
center axial member yields at an early stage, and the axial member
can be made to function as a hysteresis damper as shown in FIGS. 3
(a) and 3 (b) exhibiting the relationship between a natural period
T and a story drift angle rad at a maximum response. As shown in
FIG. 3 (b), a frame of a building including columns 36 and beams 37
shows horizontal deformation (.delta..sub.1, .delta..sub.2,
.delta..sub.3) when a horizontal force 39 acts on the building. The
story drift angle at the horizontal deformation is expressed by the
formulas
R.sub.1=.delta..sub.1/h.sub.1,R.sub.2=.delta..sub.2/h.sub.2,R.sub.3=.delt-
a..sub.3/h.sub.3 wherein R.sub.1, R.sub.2 and R.sub.3 are a story
drift angle of the first floor, a story drift angle of the second
floor and a story drift angle of the third floor, respectively.
[0093] Furthermore, as shown in FIGS. 4 (a), 4 (b) and 4 (c) and
FIGS. 5 (a), 5 (b) and 5 (c), the cross-sectional area of the
steel-made center axial member 3 of a buckling restrained brace 1
is made minimum in a central portion 21 in the longitudinal
direction having a ratio of its length to the whole length in a
restricted range, and made larger at both ends 22, 23 connectively
provided to the central portion 21 in the longitudinal direction
than that in the central portion. As a result, the central portion
21 can be made to function as a hysteresis damper. Both ends 22, 23
of the member 3 can maintain an elastic state, and fracture of a
jointed portion between the buckling restrained brace 1 and a steel
structure including a column and a beam can be prevented.
[0094] Furthermore, the present invention permits using a steel
material having a yield point as high as 245 N/mm.sup.2 for the
steel-made center axial member 3 in the buckling restrained brace
1. As shown in FIGS. 6 (a), 6 (b) and 6 (c), when the length
.alpha.L.sub.B of the central portion 21 in the longitudinal
direction which has the minimum cross-sectional area in the
steel-made center axial member 3 and a restricted ratio of its
length to the whole length, and the length (1-.alpha.)L.sub.B/2 of
both ends 22, 23 in the longitudinal direction which each have a
cross-sectional area larger than that of the central portion are
each varied to increase the axial equivalent stiffness of the
steel-made center axial member 3, the steel-made center axial
member 3 has same area from one end to the other end, passing
through the central portion in the length direction of the steel
center axial member 3, and can be made to show an axial equivalent
stiffness 1.5 times as much as that of a steel-made center axial
member having a uniform cross-sectional area and show an apparent
yield point of up to 130 N/mm.sup.2. For example, in buckling
restrained brace 1 having three portion as shown in FIG. 6 (c),
(the steel-made center axial member 3 of the buckling restrained
brace is provided with the cross-sectional area A in the length
.alpha.L.sub.B of the central portion 21 in the longitudinal
direction, and the cross-sectional area .beta.A in the length
(1-.alpha.)L.sub.B/2 and has the axial equivalent stiffness
k.sub.1. Further, the steel-made center axial member 3 is provided
with same area from one end to the other end, passing through the
central portion in the length direction of the member 3 and has the
axial equivalent stiffness k.sub.0.) a buckling restrained brace 1
having three portions as shown in FIG. 6 (c) is made to have, at
each of both ends 22, 23, a cross-sectional area 2.5 times that of
the central portion (thus; .beta.), the buckling restrained brace
shows an axial stiffness 1.8 times that of a buckling restrained
brace which is the same as the above-mentioned buckling restrained
brace except that it has a uniform cross-sectional area, and an
apparent yield point reduced by a factor of 1.8. That is, the axial
stiffness of the buckling restrained brace having a uniform
cross-sectional area is expressed by the formula k.sub.0=EA/L.sub.B
(5) For example, when .alpha.=0.25 and .beta.=2.5,
k.sub.1=k.sub.0/{.alpha.+(1-.alpha.)1/.beta.}=k.sub.0/{0.25+(1-0.25)1/2.5-
}=1.8k.sub.0 (6) Therefore, when the buckling restrained brace (1)
having 3 portions is made to have a cross-sectional area at both
ends 2.5 times that in the central portion, it shows an axial
stiffness 1.8 times that of the same buckling restrained brace
except that it has a uniform cross-sectional area. Accordingly, the
steel-made center axial member of the buckling restrained brace
yields at displacement smaller by a factor of 1.8. As a result,
even when a steel material having a yield point as high as 225
N/mm.sup.2 is used therefor, since the apparent yield point of the
buckling restrained brace is up to 130 N/mm.sup.2, the buckling
restrained brace satisfactorily functions as a hysteresis damper
against an earthquake showing a ground motion acceleration as small
as from 80 to 100 gal.
[0095] Furthermore, even when the cross section at both ends in the
longitudinal direction of the steel-made center axial member of the
buckling restrained brace is made larger than that in the central
portion, an elastic state at both ends thereof cannot be maintained
if the axial member is prepared from a steel material showing large
strain hardening. When the steel material shows a strain hardening
ratio (tensile strength/yield point) of at least 1.2 (shown in FIG.
9), the axial generated at the ends of the steel-made center axial
member is expressed by the formula axial
force.gtoreq..sigma..sub.y.times.1.2 A wherein .sigma..sub.y is the
yield stress of the steel-made axial member, and A is the
cross-sectional area in the central portion thereof as shown in
FIGS. 7 (a), 7 (b) and 7 (c), and FIGS. 8 (a), 8 (b) and 8 (c).
Therefore, plastic deformation at the ends of the steel-made center
axial member can be avoided by making the cross-sectional area at
the ends thereof at least 1.2 times that in the central
portion.
[0096] Furthermore, FIGS. 10 (a) and 10 (b), and FIGS. 11 (a) and
11 (b),show the examples in which a reinforcing bar 6-1 is used as
a steel member of a buckling-constraining concrete member. Main
reinforcements 6-2 are arranged along axial direction of a buckling
restrained brace 1 and hoop reinforcements 6-3 are arranged in the
radial direction of the brace 1. Thereby, bending stiffness and
buckling effect of the buckling-constraining concrete member can be
increased.
[0097] Furthermore, when the bending stiffness and the buckling
effect of the buckling-constraining concrete member can be
increased, a continuous or discontinuous shaped member such a
continuously integrated steel member, a steel member having
openings in its surface, a spiral steel member or the like can be
used as a steel member of a buckling-constraining concrete
member.
[0098] Moreover, the problem of properly pouring concrete for the
buckling-constraining concrete member of a buckling restrained
brace at a predetermined site can be solved by attaching a lid 24
at one end of the buckling-constraining concrete member 2 as shown
in FIGS. 12 (a) and 12 (b) and FIGS. 13 (a) and 13 (b); the lid can
prevent cracked concrete from falling. In order to prevent the
movement of the buckling-constraining concrete member when the
steel-made center axial member is axially deformed by vibration
generated by an earthquake, wind power or the like, a slip stopper
25 in a protruded shape is provided thereto as shown in FIGS. 14
(a) and 14 (b) and FIGS. 15 (a) and 15 (b), whereby the
buckling-constraining concrete member can be fixed to the central
portion thereof when the steel-made center axial member is axially
deformed.
[0099] When the buckling restrained brace is to be fixing jointed
to a damping steel structure with high tension bolts, as shown in
FIGS. 22 (a), and 22 (b) and FIGS. 21 (a) and 21 (b), the surface
hardness and surface roughness of the friction face sides of both
ends 22, 23 of the steel-made center axial member, or the surface
hardness and surface roughness of the corresponding steel-made
connecting plates 27 are made larger than those of the counterpart
friction face side. Since the friction joint proof strength of one
high tension bolt is at least twice that of one high tension bolt
in ordinary fixing jointing, the number of necessary bolts can be
made half or less compared with that in ordinary fixing jointing,
and the buckling restrained brace can be fixing jointed to the
damping steel structure with the high tension bolts without
extremely enlarging the width of both ends of the steel-made center
axial member.
[0100] In order for the buckling restrained brace to absorb
micro-vibration of a degree generated by an earthquake of a small
magnitude, wind power or the like, that the steel-made center axial
member of the buckling restrained brace does not yield, at least
one set comprising three layers which are formed from a C-shaped
cross-sectional inside steel plate 29, a visco-elastic sheet 30 and
a C-shaped cross-sectional outside steel plate 31 is fastened to
each of the two sides of the buckling-constraining concrete member
2 in the buckling restrained brace 1 as shown in FIGS. 18 (a) and
18 (b). As a result of making a combination of the buckling
restrained brace 1 and the visco-elastic sheets, the visco-elastic
sheets act against very micro-vibration of such a degree that the
steel-made center axial member of the buckling restrained brace
does not yield, and absorbs the vibration energy by their shear
deformation. However, when the vibration generated by an earthquake
of a relatively large magnitude and wind power act on the buckling
restrained brace, the steel-made center axial member yields and
functions as a hysteresis damper; the buckling restrained brace can
obtain a capacity of absorbing the energy of vibration generated by
the earthquake and wind power by the sum of an energy-absorbing
capacity effected by plasticization (plastic deformation) of the
steel-made center axial member and one effected by shear
deformation of the visco-elastic sheets.
[0101] A steel structure and its building (damping steel structure)
are designed as explained below. When an earthquake of a large
magnitude acts on a steel structure 38 and its building in which
buckling restrained braces 1 are used as braces as shown in FIGS.
19 (a) and 19 (b), the buckling restrained braces alone are
plasticized, and the main structure of columns 36 and beams 37 of
the steel structure and its building maintain an elastic state
(damping steel structure) by plasticizing the buckling restrained
braces 1 alone. Since the plastic deformation portions of the
buckling restrained braces having a capacity of plastic deformation
and resistance to fatigue which have been confirmed can thus be
specified, the structural performance of the steel structure and
its building become definite. Fracture of the buckling restrained
braces and collapse of the building can therefore be avoided.
Furthermore, the main structure is restored to the original
position after the earthquake because the main structure is always
in an elastic state, and exchange of the plasticized buckling
restrained braces alone permits continued use of the steel
structure and its building.
EXAMPLE 1
[0102] An adhesion-preventive film having a ratio
(adhesion-preventive film ratio) of the film thickness to the plate
thickness of a steel-made center axial member of at least 0.5 to
10% was provided between a buckling-constraining concrete member
and the steel-made center axial member. When considering the
pressure for placing concrete 5 in manufacturing a
buckling-restraining brace 1, a lower limitation of a minimum
thickness ratio d.sub.t(min)/t of the adhesion-preventive film 4
and a steel-made center axial member 3 is preferably about 1.2%.
The adhesion-preventive film had a secant modulus in the thickness
direction of at least 0.1 N/mm.sup.2 between a point having a
compressive strain of 0% and a point having a compressive strain of
50%, and up to 21,000 N/mm.sup.2 between a point having a
compressive strain of 50% and a point having a compressive strain
of 75%. In the present example, a maximum axial strain amplitude
.DELTA..epsilon..sub.a of 4% was applied to a buckling restrained
brace having an adhesive-preventive film ratio of 4% by a tension
and compression tester. The steel-made center axial member then
showed a tension and compression hysteresis loop as shown in FIG. 2
(b), and was deformed due to yielding without buckling even on the
compression stress side. It is quite natural that in most cases the
decline of a building caused by an earthquake or wind power,
namely, the axial strain amplitude .DELTA..epsilon..sub.a of the
steel-made center axial member is still lower. Accordingly, when
the axial strain amplitude .DELTA..epsilon..sub.a thereof is
estimated to be a still lower one, the adhesion-preventive film
ratio can be decreased. Although a butyl rubber was used as an
adhesion-preventive film in the present example, any material can
be used so long as the material is an elastic or visco-elastic one
and has a secant modulus as defined in the present invention.
[0103] Concrete examples of the adhesion-preventive film material
are plastics, natural rubber, polyisoprene, polybutadiene,
styrene-butadiene rubber, ethylene-propylene rubber,
polychloroprene, polyisobutylene, asphalt, paint and a mixture of
these substances.
EXAMPLE 2
[0104] Buckling restrained braces and a damping steel structure
were clamping jointed with high tensile bolts. As shown in FIGS. 16
(a) and 16 (b) and FIGS. 17 (a) and 17 (b), steel-made connecting
plates 27 having a surface hardness (Vickers hardness) and a
surface roughness (ten point average roughness) 1.3 times larger
than the surface hardness and surface roughness of both ends 22, 23
of the steel-made center axial members were used. Alternatively, in
the friction jointing with high tension bolts mentioned above, both
ends 22, 23 of the steel-made center axial member and the steel
made-connecting plates 27 forming one friction jointing face were
joined by the following procedure: the ratio of a hardness of the
frictional surface layer portion of one of the two steel materials
to a hardness of the frictional surface layer portion of the other
steel material is at least 2.5; the depth of the surface layer
portion having a higher hardness is at least 0.2 mm; a plurality of
triangular wave-shaped or pyramidal protrusions as shown in FIGS.
22 and 23 are provided on the surface of the steel material having
a higher surface hardness in the surface layer portion, and the
height of the protrusions is from 0.2 to 1.0 mm; and the maximum
surface roughness of the surface of the steel material having a
lower hardness in the surface layer portion is made sufficiently
smaller than the height of the protrusions. Although the number of
necessary high tension bolts was 12 when conventional friction
jointing was conducted, the number of the bolts could be reduced to
6 when the present friction jointing was employed because the
friction joint proof stress per bolt in the present friction
jointing was at least doubled compared with the conventional
friction jointing. Moreover, since the number of the bolts used was
decreased, the plate width of both ends of the steel-made center
axial member and that of the steel-made connecting plates could be
made substantially comparable to or less than the width of the
buckling-constraining concrete member 2. When the buckling
restrained brace and the damping steel structure are to be stacking
jointed without using the steel-made connecting plates, the
friction face sides of both ends of the steel-made center axial
member or those of the damping steel structure are favorably made
larger than the other counterpart friction face sides.
[0105] As a result of defining the secant modulus in the thickness
direction and the adhesion-preventive film ratio of the
adhesive-preventive film between the buckling-constraining concrete
member and the steel-made center axial member, the thickness of the
adhesion-preventive film is required to have can be sufficiently
ensured during pouring concrete. Moreover, when the steel-made
center axial member yields and is plastic deformed, the expansion
in the out-of-plane direction thereof can be sufficiently absorbed,
and the local buckling thereof can be prevented.
[0106] As a result of defining the plasticized portion of a steel
material used for the steel-made center axial member, the buckling
restrained brace can be made to function as a hysteresis damper
against an earthquake of a small magnitude. Plastic deformation of
the ends of the steel-made center axial member caused by strain
hardening can be avoided by making the cross-sectional area of each
end thereof at least 1.2 times larger than that of the central
portion.
[0107] The central portion in the longitudinal direction of the
steel-made center axial member can be made to function as a
hysteresis damper by making the cross-sectional area of the central
portion minimum; an elastic state can be maintained at both ends
thereof; therefore, fracture at joints between the buckling
restrained brace and a main column-beam steel structure can be
prevented.
[0108] When a reinforcing bar is used as a steel member of a
buckling-constraining concrete member, the bending stiffness and
the buckling effect of the buckling-constraining concrete member
can be increased.
[0109] When a lid is provided to the steel-made center axial
member, pouring concrete becomes easy, and cracked concrete can be
prevented from falling.
[0110] Providing a slip stopper to the steel-made center axial
member produces the following-results. The buckling-constraining
concrete member can be fixed to the central portion thereof; the
clearance between the buckling-constraining concrete member and
each expanded portion of both ends in the longitudinal direction
thereof becomes definite, and the design can be easily made; the
buckling-constraining concrete member can be prevented from
gravity-caused slipping down.
[0111] According to the present invention, the friction joint proof
stress can be made at least twice larger than that of the
conventional bolt joint. As a result, the number of necessary bolts
can be made half or less, and the buckling restrained brace and the
damping steel structure can be fixing jointed with high tensile
bolts without extremely expanding both ends of the steel-made
center axial member.
[0112] Making a combination of the buckling restrained brace and
the visco-elastic sheets in parallel for the purpose of absorbing
energy of earthquakes of large and small magnitudes permits always
absorbing vibration energy without depending on the magnitude of
excited vibration amplitudes. Moreover, the absorbing capacity can
be made larger than that of the buckling restrained brace
alone.
[0113] When an earthquake of a large magnitude acts on a steel
structure and its building in which buckling restrained braces are
used as braces, the main structure is restored to the original
position after the earthquake because the main structure is always
in an elastic state, and continued use of the steel structure and
its building is readily permitted by exchanging the plasticized
buckling restrained braces alone.
* * * * *