AN ABSTRACT OF THE THESIS OF
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AN ABSTRACT OF THE THESIS OF
James D. Newell for the degree of Master of Science in Civil Engineering
presented on April 22, 2003.
Title: Steel Confined Yielding Damper for Earthguake Resistant Design
Abstract Approved:
Redacted for Privacy
Christ'pher C. Higgins
An experimental study of a passive energy dissipation tensioncompression yielding brace or buckling restrained brace has been
conducted. The Confined Yielding Damper (CYD) consists of a steel
yielding core confined within a tube filled with non-cohesive media. The
external tube and confined non-cohesive media provide lateral stability
to the core enabling the device to yield in compression as well as
tension.
This device is similar to the Unbonded Brace developed by
Nippon Steel of Japan.
Fourteen full-scale CYDs were tested to
determine the effect of varied confining media, perforation blocking
configuration, and a random displacement history. Based on the
Confined Yielding Dampers tested relatively stable and symmetric
hysteretic damping can be achieved with the CYD device.
©Copyright by James D. Newell
April 22, 2003
All rights reserved
Steel Confined Yielding Damper for Earthquake Resistant Design
by
James D. Newell
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Presented April 22, 2003
Commencement June 2003
Master of Science thesis of James D. Newell presented on April 22, 2003.
APPROVED:
Redacted for Privacy
Major Professor, representing Civil Engineering
Redacted for Privacy
Head of the Department of Civil, Construction, and Environmental
Engineering
Redacted for Privacy
Dean of the Graduate School
I understand that my thesis will become part of the permanent collection of
Oregon State University libraries. My signature below authorizes release
of my thesis to any reader upon request.
Redacted for Privacy
James D. Newell, Author
ACKNOWLEDGEMENTS
The author would like to express sincere appreciation to Major
Professor Dr. Christopher Higgins. Without his guidance, support, and
hard work this thesis would not have been possible. Additionally the
author would like to thank committee members Dr. Thomas Miller, Dr.
David Rosowsky, and Dr. David Gobeli.
This research was funded by the National Science Foundation
(NSF) under Grant No. CMS-0099701 as part of the US-Japan
Cooperative Research in Urban Earthquake Disaster Mitigation Program.
Professor K. Kasai of the Tokyo Institute of Technology was the Japanese
counterpart and Dr. Peter Chang was the program manager. Additional
funding from the 2002 AISC/Klingelhofer Fellowship supported this
research. Their support is gratefully acknowledged. The opinions, findings,
and conclusions are those of the author and do not necessarily reflect the
views of NSF, AISC, or the individuals acknowledged above.
TABLE OF CONTENTS
Page
INTRODUCTION and BACKGROUND
1
EXPERIMENTAL PROGRAM
5
Test Specimens
5
Structural Testing Matrix
15
Specimen Fabrication
17
Structural Testing Setup
21
Increasing Amplitude Displacement Protocol
28
Random Displacement History Development
30
EXPERIMENTAL RESULTS
40
Parameters Used for Comparison
40
Test Observations
40
Confining Media Effects
43
Perforation Blocking Effects
49
Decreasing Amplitude Displacement History
53
Random Displacement History
55
CONCLUSIONS
65
BIBLIOGRAPHY
68
APPENDIX
70
LIST OF FIGURES
Figure
Page
1.
CYD configurations.
6
2.
CYD cross-sections.
7
3.
Prototype frame with CYDs.
9
4.
Yielding core geometries.
11
5.
CYD blocking configurations used with 125 kip perforated
specimens.
18
CYD blocking configuration used with 50 kip perforated
specimens.
19
7.
Experimental setup.
22
8.
Yielding core strain gage configuration used on 125 kip
specimens.
24
9.
Yielding core strain gage configuration used on 50 kip
specimens.
25
10.
Confining tube strain gage configurations.
26
11.
Instrumentation plan.
27
12.
Increasing amplitude displacement protocol imposed on
most test specimens.
29
Three-story building plan (Sabelli, 2000) used for
time history analysis.
31
14.
Three-story BRBF model.
32
15.
First story BRB axial displacement time history for LA2O.
38
16.
Simplified random displacement history imposed on
specimen 5ODB-2.
39
6.
13.
LIST OF FIGURES (Continued)
Page
Figure
17.
Specimen 125DB-2 hysteresis.
44
18.
Specimen 50DB-i hysteresis.
45
19.
Specimen 125DB-3 hysteresis.
47
20.
Specimen 125P-i hysteresis.
50
21.
Specimen 125P-5 hysteresis.
52
22.
Specimen 50P-1 hysteresis.
54
23.
Specimen 50P-2 hysteresis.
56
24.
Specimen 50P-2 hysteresis for each iteration of imposed
random displacement history.
57
25.
Experimental and analytical force-deformation response for
specimen 50P-2 during second iteration of imposed random
displacement history.
60
Analytically predicted BRB axial displacement in the first
story time history using theoretical CYD response and
modified based on experimental results.
62
Analytically predicted roof displacement time history using
theoretical CYD response and modified based on
experimental results.
63
26.
27.
LIST OF TABLES
Table
Page
1.
Yielding Core Properties
12
2.
Test Matrix
16
3.
Confining Media Properties
20
4.
Three-Story BRBF Model Member Properties
33
5.
Three-Story Building Design Loads
35
6.
Three-Story BRBF Model Loads
35
7.
CYD Performance Summary
41
8.
Random Displacement History Iteration Comparison
58
9.
Nonlinear Dynamic Time History Results
64
LIST OF APPENDIX FIGURES
Figure
Page
Al.
Specimen 125DB-i Buckled Shape
71
A2.
Specimen 125DB-i Hysteresis
71
A3.
Specimen 125DB-i Displacement
72
A4.
Specimen 125DB-i String Pot Displacement
72
A5.
Specimen 125DB-i Yielding Core/Confining Tube
Relative Displacement
73
A6.
Specimen 125DB-i Threaded Rod Load
73
A7.
Specimen 125DB-2 Buckled Shape
74
A8.
Specimen 125DB-2 Hysteresis
74
A9.
Specimen 125DB-2 Displacement
75
AlO. Specimen 125DB-2 String Pot Displacement
Al 1.
Specimen 1 25DB-2 Yielding Core/Confining Tube
Relative Displacement
75
76
Al2. Specimen 125DB-2 Confining Tube Axial Load
76
A13.
Specimen 125DB-3 Buckled Shape
77
A14.
Specimen 125DB-3 Hysteresis
77
A15.
Specimen 125DB-3 Displacement
78
A16.
Specimen 125DB-3 String Pot Displacement
78
Al 7. Specimen 1 25DB-3 Yielding Core/Confining Tube
Relative Displacement
79
Ai8. Specimen 125DB-3 Yielding Core Strain Gages D-G3, 4
79
LIST OF APPENDIX FIGURES (Continued)
Page
Figure
A19.
Specimen 125DB-4 Buckled Shape
80
A20.
Specimen 125DB-4 Hysteresis
80
A21.
Specimen 125DB-4 Displacement
81
A22. Specimen 125DB-4 String Pot Displacement
A23.
81
Specimen I 25DB-4 Yielding Core/Confining Tube
Relative Displacement
82
A24.
Specimen 125DB-4 Confining Tube Strain Gages N-I, B
82
A25.
Specimen 125DB-5 Buckled Shape
83
A26.
Specimen I 25DB-5 Hysteresis
83
A27. Specimen 125DB-5 Displacement
84
A28.
Specimen 125DB-5 String Pot Displacement
84
A29.
Specimen 125DB-5 Yielding Core/Confining Tube
Relative Displacement
85
A30. Specimen 125DB-5 Confining Tube Strain Gages S-E, W
85
A31.
Specimen 125P-1 Buckled Shape
86
A32.
Specimen 125P-1 Hysteresis
86
A33.
Specimen 125P-1 Displacement
87
A34.
Specimen 125P-1 String Pot Displacement
87
A35.
Specimen 125P-1 Yielding Core/Confining Tube
Relative Displacement
88
Specimen 125P-1 Yielding Core Load, Location A-Leg 1,2
88
A36.
LIST OF APPENDIX FIGURES (Continued)
Figure
Page
A37.
Specimen 125P-2 Buckled Shape
89
A38.
Specimen 125P-2 Hysteresis
89
A39.
Specimen 125P-2 Displacement
90
A40.
Specimen 125P-2 String Pot Displacement
90
A41.
Specimen 125P-2 Yielding Core/Confining Tube
Relative Displacement
91
A42.
Specimen 125P-2 Yielding Core Load, Location A-Leg 1,2
91
A43.
Specimen 125P-3 Buckled Shape
92
A44.
Specimen 125P-3 Hysteresis
92
A45. Specimen 125P-3 Displacement
93
A46.
Specimen 125P-3 String Pot Displacement
93
A47.
Specimen 125P-3 Yielding Core/Confining Tube
Relative Displacement
94
A48.
Specimen 125P-3 Confining Tube Strain Gages N-F, W
94
A49. Specimen 125P-4 Buckled Shape
A50.
Specimen 125P-4 Hysteresis
A51. Specimen 125P-4 Displacement
95
95
96
A52.
Specimen 125P-4 String Pot Displacement
96
A53.
Specimen 125P-4 Yielding Core/Confining Tube
Relative Displacement
97
Specimen 125P-4 Load Cell, Yielding Core Strain Gages
Location D + Confining Tube Strain Gages Location S
97
A54.
LIST OF APPENDIX FIGURES (Continued)
Figure
Page
A55. Specimen 125P-5 Buckled Shape
98
A56. Specimen 125P-5 Hysteresis
98
A57. Specimen 125P-5 Displacement
99
A58. Specimen 125P-5 String Pot Displacement
99
A59. Specimen 125P-5 Yielding Core/Confining Tube
Relative Displacement
100
A60. Specimen 125P-5 Load Cell, Yielding Core Strain Gages
Location D + Confining Tube Strain Gages Location S
100
A61. Specimen 50DB-i Buckled Shape
101
A62. Specimen 50DB-i Hysteresis
101
A63. Specimen 50DB-I Displacement
102
A64. Specimen 50DB-i String Pot Displacement
102
A65. Specimen 50DB-i Yielding Core/Confining Tube
Relative Displacement
103
A66. Specimen 50DB-i Yielding Core Strain Gages A-Gi, 2
103
A67. Specimen 5ODB-2 Buckled Shape
104
A68. Specimen 5ODB-2 Hysteresis
104
A69. Specimen SODB-2 Displacement
105
A70. Specimen 5ODB-2 String Pot Displacement
105
A7i. Specimen 5ODB-2 Yielding Core/Confining Tube
Relative Displacement
106
A72. Specimen 5ODB-2 Threaded Rod Load
106
LIST OF APPENDIX FIGURES (Continued)
Figure
Page
A73.
Specimen 50P-1 Buckled Shape
107
A74.
Specimen 50P-1 Hysteresis
107
A75.
Specimen 50P-1 Displacement
108
A76. Specimen 50P-1 String Pot Displacement
A77.
A78.
108
Specimen 50P-1 Yielding Core/Confining Tube
Relative Displacement
109
Specimen 50P-1 Yielding Core Strain Gages A-G3, 4
109
A79. Specimen 50P-2 Buckled Shape
110
A80. Specimen 50P-2 Hysteresis
110
A81. Specimen 50P-2 Displacement
111
A82.
111
Specimen 50P-2 String Pot Displacement
A83. Specimen 50P-2 Yielding Core/Confining Tube
Relative Displacement
112
A84.
112
Specimen 50P-2 Confining Tube Axial Load
Steel Confined Yielding Damper for
Earthquake Resistant Design
INTRODUCTION and BACKGROUND
In the United States there is a shift toward performance based
design of structures and an increased demand for higher performance
levels for structures during earthquakes. Building owners are increasingly
interested in immediate occupancy following large earthquakes and want to
mitigate economic losses due to structural damage during a seismic event.
One method for protecting structures and achieving higher performance
levels
is
the
application
of passive
energy dissipaters.
Viscous,
viscoelastic, and metallic dampers are types of passive dampers currently
being used to increase the performance level of structures during seismic
events. While viscous and viscoelastic dampers are becoming more
common, application of metallic dampers has recently begun to increase in
the U.S.
Metallic dampers rely on the hysteretic damping capacity of the
metal component of the device and the post-yield properties of the metallic
elements to provide the design level of ductility and energy dissipation. The
1997 Uniform Building Code (UBC) permits inelastic deformation of
structural members during the design level earthquake. If this were not
allowed member sizes required to ensure elastic performance during the
2
design earthquake would be much larger and prohibitively costly. The
metallic damper system utilizes the inelastic deformation allowance of the
UBC by providing elements designed to dissipate the input seismic energy
through controlled cyclic inelastic deformations.
One such metallic damper, a tension-compression yielding brace or
buckling-restrained brace (BRB) termed the Unbonded BraceTM (UBB) has
been developed by Nippon Steel of Japan (Aiken, et al. 2000; B'ack, et al.
2002; Wantanabe, 1992; Wantanabe, et al. 1998). The damper relies upon
a structural tube filled with mortar that confines a steel yielding core. This
steel core is similar to diagonal bracing in a typical braced frame. A
debonding agent is applied between the concrete and steel allowing space
for Poisson's effect and reduces shear stress transfer between the steel
yielding core, mortar, and confining tube. The thickness of this debonding
agent is critical to the performance of the damper system and must be
carefully designed and fabricated. The mortar provides buckling resistance
that allows the steel core to yield in compression as well as the typical
yielding in tension, thereby permitting stable and symmetric hysteretic
energy dissipation capacity under fully reversed cyclic loading. To ensure
that the damper does not buckle in the first mode as an ordinary brace
would, the UBB must satisfy the following condition:
L2
aP
(1)
3
where: E = Young's Modulus; I = moment of inertia of the outer confining
tube; L = brace length, taken as work point to work point; a = global
buckling factor of safety; P = design axial load including the effects of strain
hardening (Wantanabe, 1992). Any contribution of the mortar to the
moment of inertia is neglected due to the assumption that the mortar is
cracked during cyclic loading (Wantanabe, 1992; Wantanabe, et al. 1988).
When the conditions of this equation are met, the external structural tube
will provide the necessary global buckling resistance and enable the steel
core to yield in compression instead of global brace buckling in first mode.
Tests conducted both in Japan and the United States to assess the
performance of UBBs indicated the device provides stable, reasonably
symmetric hysteretic energy dissipation of the input cyclic loading (Aiken,
et al. 2000; Black, et al. 2002; Wantanabe, 1992; Wantanabe, et al. 1998).
Buckling-restrained braced frames (BRBF) with UBBs have seen
over 200 Japanese applications since 1987 (Black, et al. 2002) and are
gaining increased acceptance as a seismic force resisting system (SFRS)
by the U.S. structural engineering community. BRBFs have been used in
13 U.S. projects to date, including both new and retrofit construction
(Black, et al. 2002). All applications have used imported Nippon Steel
UBBs from Japan. Currently no adopted U.S. code provisions exist for
BRBF design. A draft document is under development by a joint American
Institute of Steel Construction I Structural Engineers Association of
California (AISC/SEOC) committee and it is anticipated this work will be
incorporated into the 2007 A/SC Seismic Provisions for Structural Steel
Buildings.
This paper addresses an alternative form of BRB in which the
mortar used to fill the confining tube of the UBB is replaced with confined
non-cohesive media. This non-cohesive media is placed under a normal
confining force to provide buckling resistance of the core enabling the
device to yield in compression. Confined Yielding Dampers (CYDs) provide
benefits including economical use of standard materials, for example, A36
steel bar stock for the yielding core and A53A steel pipe for the confining
tube. Further, this new device offers simplified connection design and
detailing, opens the market for U.S. fabrication of CYDs using no patented
technologies, reduces costs associated with importing BRBs from Japan
(most current U.S. projects use UBBs imported though Nippon Steel),
applicability to a wider range of building structures as the brace yield force
levels under investigation are lower than are currently available, post event
inspection, and simplified design of the damper device because the
debonding layer required in UBBs is not necessary.
EXPERIMENTAL PROGRAM
Test Specimens
Small scale experimental CYD tests were carried out at Clarkson
University (Higgins and Newell, 2001; Higgins and Newell, 2002). Test
results indicated relatively stable and symmetric hysteretic damping with a
reduced scale device. The current testing
program was therefore
undertaken to characterize full-scale CYD performance and establish
design guidelines for future application of CYDs as a SFRS in structures.
Four yielding core configurations were investigated: 125 kip (556
kN) yield force in a dog bone configuration, 125 kip (556 kN) yield force in
a perforated configuration, 50 kip (222 kN) yield force in a dog bone
configuration, and 50 kip (222 kN) yield force in a perforated configuration.
The CYD configurations, illustrated in Fig. 1, consist of a steel yielding core
element within a steel pipe filled with a confined non-cohesive media. The
non-cohesive media takes the place of the mortar used in the UBB in
providing lateral stability to the yielding core, enabling yielding of the core
in compression cycles. A constant confining media volume was maintained
with steel end caps and 1/2 in. (12.70 mm) diameter A193 B-7 high
strength threaded rod. Specimen cross-sections are shown in Fig. 2.
To develop a realistic sized brace for testing, a prototype structure
was used. A full-scale specimen yielding core length of 16 ft. (4.88 m) was
125DB
6-1" Dia.
Bolts
1/2 in. Dia. High Strength Threaded Rod
'-8 in. Extra Heavy Steel Pipe
I 25P
00
00
0 01
5-" Dia. A490 Bolts
50DB
in. Extra Heavy Steel Pipe
'S.
16ft.
Figure 1: CYD configurations.
125 kip CYD
Cross-Section
Non-cohesive Confining Media
A193 B-7 1/2 in. Dia.
High Strength Threaded Rod
A36 Steel Yielding Core
125 kip CYD Unreduced Section
(1-114 in. x 6 in.)
8 in. Extra Strong
A53A Steel Pipe
A36 Steel Yielding Core
Dog Bone Reduced Section
(1-1/4 in. x 1-15/16 in.)
Non-cohesive Confining
A193 B-7 1/2 in. Dia.
High Strength Threaded Rod
A36 Steel Yielding Core
50 kip CYD Unreduced Section
(3/4 in. x 4-1/2 in.)
6 in. Extra Strong
A53A Steel Pipe
Figure 2: CYD cross-sections.
A36 Steel Yielding Core
Dog Bone Reduced Section
(3/4 in. x 1-11/16 in.)
selected for a single diagonal brace in a typical bay with column-to-column
centerline spacing of 15 ft. (4.57 m), beam-to-beam centerline spacing of
13 ft. (3.96 m) and considering the gusset plate beam to column to brace
connection, as illustrated in Fig. 3.
In this research two different yield force levels were investigated:
125 kip (556 kN) and a 50 kip (222 kN) yield force levels. A dog bone and
perforated yielding core configuration were tested at each force level. The
yielding core reduced cross-sectional area was calculated based on the
desired yield force and material properties determined from tension coupon
testing. The dog bone configuration is typical of current BRBs. The
perforated configuration has the potential for greater variation in the yield
force and stiffness of the device by varying geometric properties and was
therefore investigated. The legs of different perforations could be fabricated
to different lengths, cross-sectional areas or tapered allowing for tailoring of
device performance.
Specimens were named by yield force level, yielding core
configuration, and specimen identification number. 125DB-i was a 125 kip
(556 kN) yield force, dog bone configuration, and specimen identification
number I.
50P-2 was a 50 kip (222 kN) yield
force, perforated
configuration, and specimen identification number 2.
The 125 kip yield force dampers consisted of 1-1/4 in. (31.75 mm)
by 6 in. (152.40 mm) A36 steel bar stock with a yield stress of 51.8 ksi
- Structural Steel Frame
A992
Mild Steel (A36) Yielding Damper
Yield Force = 125 kips
I
13ft
Steel
I
pe
High-Strength Structural Bolts
A490
I
151t
I
Figure 3: Prototype frame with CYDs.
15ft
:
10
(357.2 MPa) and an ultimate stress of 72.1 ksi (497.1 MPa), based on
tension coupon testing. The reduced cross-sectional area of the 125DB
specimen was 2.422
in2
(1562.6 mm2) and the reduced cross-sectional
area of each leg of the 125P specimen was 1.211
in2
(781.3 mm2) resulting
in an area for both legs equivalent to that of the dog bone specimen.
Length of individual perforation legs was 11 in. (279.40 mm) with a 2.3
factor of safety against buckling assuming pinned ends. Yielding core
geometry for all specimens is shown in Fig. 4. Elastic stiffness and yield
displacement of the 125DB specimens were 451 kip/in (79.0 kN/mm) and
0.278 in. (7.06 mm), respectively, and for the 125P specimens were 581
kip/in (101.7 kN/mm) and 0.216 in. (5.49 mm). These stiffness and yield
displacement values are summarized in Table 1 and take into account the
unreduced sections of the yielding core that remain elastic after the
reduced sections have yielded up to the first line of bolts. Connections for
both 125 kip (556 kN) yield force configurations were detailed as slip-
critical bolted connections with class A slip surfaces and six (6) fully
tensioned 1 in. (25.40 mm) diameter A490 high strength structural bolts at
each end of the brace designed per 1993 Load and Resistance Factor
Design Specification for Structural Steel Buildings (AISC, 1993). Slip
critical connections were designed for the ultimate strength of the steel
yielding core taking into account the compressive overstrength factor of 1.1
typical of previously tested BRBs (Aiken, et al. 2000). A490 high strength
192 in.H19y2
.7
14516 in.
in.
igj/2
)
L26 in.
Lft2l,6
6in.[
1
1-1/4 in. A36 Steel Bar
192 in.
ø46in.J
i ,125P
fl219%5 in.H
in.
1r1.
)
11 in.
6 in.
D
1-1/4 in. A36 Steel Bar Stock"
in.
-192 in.-
L
17 in.
L246
in.' ø21%6 n.
7 in.
52946 in.
16 in.
o1 50DB
3/4 in. A36 Steel Bar
Li%in
192 in.
in.T
4Y2
125DB
9in.
L216 in.
)CP
2%6in.
in.
C
)
24%6 in.H
c°°150P
3/4 in. A36 Steel Bar
Figure 4: Yielding core geometries.
-
Table 1: Yielding Core Properties
Specimen
Yield Stress
Area of
Reduced
Cross-Section
Yield
Force
F
(ksi)
(1)
125DB
125P
50DB
50P
51.8
51.8
39.5
39.5
Yield
Displacement
Local Brace
Stiffness
K
Py
(MPa)
(mm2)
(kip)
(2)
(3)
357.2 2.422 1562.6
357.2 2.422 1562.6
272.4 1.266 816.8
272.4 1.266 816.8
125
125
50
50
(in2)
(kN)
(4)
556
556
222
222
(in)
(mm) (kip/in) (kN/mm)
(5)
0.278 7.06
0.216 5.49
0.222 5.64
0.174 4.42
451
581
225
287
(6)
79.0
101.7
39.4
50.3
F\)
13
structural bolts were used because there fully tensioned slip-critical
capacity is greater than A325 high strength structural bolts and thus
connection geometry could be shortened. The calculated 202.8 kip (902.1
kN) slip capacity of the bolted connection was 1.06 times greater than the
192.1 kip (854.5 kN) ultimate compressive strength of the yielding core.
Connection net section was designed to remain elastic at a load equal to
yielding core ultimate tensile strength. Yielding core stress on the net
section at the first line of bolts was calculated to be 37.3 ksi (257.2 MPa)
for this case. Washers were used under both the head of the bolt and nut
per RCSC
Specification
for Structural Joints (RCSC, 1994) for steel with a
nominal yield stress less than 40 ksi (275.8 MPa). The two splice plates
per connection used to join yielding core and reaction system were 3/4 in.
(25.4 mm) by 6 in. (152.40 mm) A36 steel bar stock. The confining tube for
the 125 kip (556 kN) yield force specimens was an 8 in. (203.20 mm) extra
heavy steel pipe (A53A) with a factor of safety against global buckling of
2.7 assuming pin ended connections, work point to work point on the brace
length, and considering the ultimate compressive strength of the yielding
core.
The 50 kip (222 kN) yield force dampers consisted of 3/4 in. (19.05
mm) by 4-1/2 in. (114.30 mm) A36 steel bar stock with a yield stress of
39.5 ksi (272.4 MPa) and an ultimate stress of 63.6 ksi (438.5 MPa) based
on tension coupon testing. The reduced cross-sectional area of the 50DB
14
specimen was 1.266
in2
(816.7 mm2) and the reduced cross-sectional area
of each leg of the 50P specimen was 0.633
in2
(408.4 mm2) providing an
area of both legs equivalent to that of the dog bone specimen. Length of
individual perforation legs was 9 in. with a 2.4 factor of safety against
buckling assuming pinned ends. Yielding core geometry is shown in Fig. 4.
Elastic stiffness and yield displacement of the 50DB specimens were 225
kip/in (39.4 kN/mm) and 0.222 in. (5.64 mm), respectively, and for the 50P
specimens were 287 kip/in (50.3 kN/mm) and 0.174 in. (4.42 mm). These
values are summarized in Table I and take into account the unreduced
sections of the yielding core that remain elastic after the reduced sections
have yielded up to the first line of bolts. Connections for both of these 50
kip (222 kN) yield force configurations were detailed as slip-critical bolted
connections with class A slip surfaces and five (5) fully tensioned 314 in.
diameter A490 high strength structural bolts at each end of the brace
designed per 1993 Load and Resistance Factor Design Specification for
Structural Steel Buildings (AISC, 1993). Slip-critical connections were
designed for the ultimate strength of the steel yielding core taking into
account the compressive overstrength factor of 1.1 typical of previously
tested BRBs (Aiken, et al. 2000). The calculated 92.4 kip (411.0 kN) slip
capacity of the bolted connection was 1.04 times greater than the 88.5 kip
(393.6 kN) ultimate compressive strength of the yielding core. Connection
net section was designed to remain elastic at a load equal to yielding core
15
ultimate tensile strength. Yielding core stress on the net section at the first
single bolt was calculated to be 29.6 ksi (204.1 MPa) and at the first line of
two bolts the stress was 31.2 ksi (215.1 kN) for this case. Washers were
used under both the head of the bolt and nut per RCSC Specification for
Structural Joints (RCSC, 1994) for steel with a nominal yield stress less
than 40 ksi (275.8 MPa). The two splice plates per connection used to join
yielding core and reaction system were 1 in. (25.4 mm) by 6 in. (152.40
mm) A36 steel bar stock. The confining tube for the 50 kip (222 kN) yield
force specimens was a 6 in. (152.40 mm) extra heavy steel pipe (A53A)
with a factor of safety against buckling of 2.3 assuming pin ended
connections, work point to work point brace length, and considering the
ultimate compressive strength of the yielding core.
Structural Testing Matrix
Fourteen full-scale CYDs were tested to characterize device
performance and investigate the influence of various parameters on
behavior as shown in the testing matrix, Table 2. The effects of different
confining media were investigated using the 125 DB specimens. Four
different readily available aggregates were used as confining media: sand,
pea gravel (1/4 in. (6.35 mm) minus gravel), 3/4 in. (19.05 mm) to #4
gravel, and 3/4 in. (19.05 mm) minus gravel (which consisted of equal parts
of the above). Pea gravel was used as the confining media for all other
16
Table 2: Test Matrix
Specimen
(1)
125DB-i
125DB-2
125DB-3
125DB-4
125DB-5
Parameter
(2)
Pea Gravel
Pea Gravel (Pencil Vibrator)
Sand
3/4" - #4 Gravel
3/4" minus Gravel
125P-i
125P2
All perforations spray foamed
First perforation @ each end completely blocked,
remaining perforations with spray foamed radius
125P-3
First 2 perforations
each end completely blocked,
remaining perforations with spray foamed radius
125P-4
First 2 perforations
each end completely blocked,
remaining perforations blocked with knockout minus
2 in. length (with cut in middle of knockout)
125P-5
First 2 perforations
each end completely blocked,
remaining perforations blocked with plate minus
2 in. length, minus 1/2 in. width
50DB-i
500B-2
Increasing amplitude displacement protocol
Reverse displacement protocol from 2.0 ibm
50P-i
Increasing amplitude displacement protocol
Random displacement history
50P-2
@
DB Dog bone configuration
P Perforated configuration
17
specimens. Different configurations of perforation blocking (Fig. 5) were
tested with the 125P specimens to optimize performance and minimize first
mode buckling of individual legs. A decreasing amplitude displacement
history was compared to the typical increasing amplitude displacement
protocol with the 50DB specimens. CYD performance when subjected to a
random displacement history was evaluated with the 50P specimens with
perforation blocking as shown in Fig. 6.
Specimen Fabrication
The dog bone and perforated configuration yielding cores were
fabricated using abrasive water jet cutting techniques. A 50,000 psi (344.75
MPa) water and garnet abrasive culling stream was CNC controlled to cut
the required configurations. Testing of both water jet and traditionally
machined tension coupons did not indicate a change in the stress-strain
behavior from the water jet culling process of the 1-1/4 in. (31.75 mm) A36
steel bar stock used for the 125 kip (556 kN) yielding cores.
The weight of confining media placed in the tube was calculated to
achieve approximate 95% relative density. Actual confining media
volumes, weights, and densities are given in Table 3. The tube was filled
with confining media in a vertical orientation with the yielding core
maintained
in
proper
alignment.
Confining
media was placed
approximately 30 lb (0.13 kN) lifts and compacted internally with a pencil
in
ii;]
Center Line
of Brace
- 88888
88888
ES88
Center Line
of Brace
oo
0
000
125P-2
Center Line
of Brace
000
000
______
______
______
____
1 25P-3
Center Line
of Brace
____ ____
1 25P-4
Cut in Steel Blocking
Center Line
of Brace
125P-5
Steel Blocking (same thickness as yielding core)
Spray Foam Blocking (same thickness as yielding core)
Figure 5: CYD blocking configurations used with
125 kip perforated specimens.
19
Center Line
of Brace
Steel Blocking (same thickness as yielding core)
Spray Foam Blocking (same thickness as yielding core)
Figure 6: CYD blocking configuration used with
50 kip perforated specimens.
Table 3: Confining Media Properties
T
Weight of
Compaction T
Method
Confining Media
Specimen
Confining Media
(1)
(2)
(3)
125DB-i
Pea Gravel
Pea Gravel
Sand
DBH/PV
125DB-2
125DB-3
125DB-4
125DB-5
3/4"-#4 Gravel
3/4"
-
minus Gravel
DBH
(lb)
(kN)
Volume of
Voids
DBH
DBH
DBH
412.00
438.50
382.50
400.00
466.75
(m3)
(ft3)
(4)
Confining Media
Density
(lb/ft3)
(5)
1.83
1.95
1.70
1.78
2.08
(kN/m3)
(6)
3.88
3.85
3.86
3.88
3.88
0.1099
0.1090
0.1093
0.1099
0.1099
106.19
113.90
99.09
103.09
120.30
16.68
17.89
15.56
16.19
18.89
125P-1
125P-2
125P-3
125P-4
125P-5
Pea Gravel
Pea Gravel
Pea Gravel
Pea Gravel
Pea Gravel
DBH
DBH
DBH
DBH
DBH/PV
361.75
390.25
375.75
356.00
387.50
1.61
1.74
1.67
1.58
1.72
3.46
3.66
3.59
3.46
3.44
0.0980
0.1037
0.1017
0.0980
0.0974
104.55
106.63
104.67
102.89
112.65
16.42
16.75
16.44
16.16
17.69
50DB-I
PeaGravel
PeaGravel
DBH/PV
DBH/PV
265.75
268.25
1.18
1.19
2.28
2.28
0.0646
0.0646
116.56
117.65
18.31
Pea Gravel
Pea Gravel
DBH/PV
DBH/PV
236.00
231.25
1.05
1.03
2.10
2.10
0.0595
0.0595
112.38
110.12
17.65
17.30
5ODB-2
50P-1
50P-2
18.48
DB Dog bone configuration
P Perforated configuration
DBH Dead blow hammer
PV Pencil vibrator
T\)
21
vibrator and/or externally with a 5 lb (0.02 kN) dead blow hammer on the
outside of the confining tube. Method of compaction is included in Table 3.
The confining media volume was maintained with steel end caps and 1/2
in.
(12.70 mm) diameter A193 B-7 high strength threaded rod. The
threaded rod was encased in concrete prestressing strand sheathing to
reduce interaction between the threaded rod and confining media. Six 700
lb (3.11 kN) Beilville Washers stacked in series were used at one end of
the threaded rod to maintain approximately 2 kip (8.90 kN) of confining
force per threaded rod. Sheet metal and spray foam crush-zones 6 in.
(152.40 mm) in length were added to the dog bone yielding cores in the
transition zone from reduced to unreduced cross section to minimize the
effects (compressive stiffening) of the shoulders of the dog bone yielding
core bearing on the confining media. Perforated specimens were encased
in sheet metal to maintain alignment of blocking material within individual
perforations.
Structural Testing Setup
Specimens were tested in a horizontal configuration, Fig. 7, with a
structural steel reaction system at each end attached to the strong floor.
Roller supports were provided at approximate third points of the confining
tube to protect the test setup from any overall damper instability. The
rollers provided negligible resistance to tube movement in the brace axial
Reaction
Hydraulic Actuator
Splice Plate
/(each side)
Roller Suppo
CYD Secimen
=
Reaction System
Strong Floor
Figure 7: Experimental setup.
[]
23
direction but prevented any excessive deformation in the transverse
directions. Load was applied at a rate of 1.33 in/mm (33.78 mm/mm) with a
500 kip (2224 kN) capacity servo-controlled hydraulic actuator. Specimen
yielding core axial deformation was used as the feedback sensor for the
servo-control system. Instrumentation consisted of strain gages, force
washer load cells, displacement transducers and an in-line load cell. Strain
gages on the steel yielding cores were placed to measure axial strain and
determine if the yielding core was bending within the elastic range of the
gages used. Strain gages were bonded to the middle of each face of the
steel yielding core as shown in Fig. 8 for the 125 kip (556 kN) specimens
and Fig. 9 for the 50 kip (222 kN) specimens. Strain gages on the confining
tube were placed to measure axial strain and determine if the confining
tube was bending. Strain gages were bonded at 90° orientations from each
other around the circumference of the pipe at the middle and north quarter
point (Fig. 10). Force washer load cells were used to measure the force in
the 1/2 in. (12.70 mm) diameter A193 B-7 high strength threaded rod used
to maintain confining media volume and their orientation is shown in Fig.
11. Two displacement sensors (string potentiometers) (Fig. 11) were used
to measure overall yielding core deformation. Displacement values from
these two sensors were averaged to remove any bending component due
to brace end rotation outside of the confining tube. Two other displacement
sensors measured relative deformation of the yielding core into and out of
162/6 in.
86%6 in.
296 n
125DB
GI
x . Denotes strain gaged location
Section a-a
G41G3
G2
1 25P
x - Denotes strain gaged location
Section
b-b
(ryp.)
Figure 8: Yielding core strain gage configuration used on 125 kip specimens.
886in.
I
16113/;6 rn
-
303%6ir.
50DB
Gi
x - Denotes strain gaged location
G4IG3
Section a-a
YP)
G2
50P
x - Denotes strain gaged location
G4
Section b-b
(Typ.)
G8
Figure 9: Yielding core strain gage configuration used on 50 kip specimens.
161 in.
80Y2 in
403/4 in.
P
125DB
1 25P
x - Denotes strain gaged location
I
wQE
Section a-a
(Typ.)
B
166 in.
83 in.
42 in.
50DB
50P
x - Denotes strain gaged location
I
WQE
Section b-b
(Typ.)
B
Figure 10: Confining tube strain gage configurations.
N.)
a)
Hydraulic Actuator
Reaction
Roller Support
Load Cell
-
-\
CYD Specimen
+ Displacement Sensor
(arrow indicates
positive direction)
Washer Load Cell
Figure 11: Instrumentation plan.
4NJ
the confining tube at each end, shown in Fig. 11. A PC-based data
acquisition system was used to acquire data at a continuous rate of 5 Hz
during testing.
Increasing Amplitude Displacement Protocol
The displacement protocol (Fig. 12) was based on the guidelines of
ATC 24 (ATC, 1992) and the draft AISC/SEAOC Recommended Buckling-
Restrained Brace Frame Provisions (AISC/SEAOC, 2001). Increasing
amplitude fully reversed cyclic axial displacement was applied until failure.
Two cycles each were applied at 0.25
by 0.50
by, and 0.75 Aby, where
Aby is equal to the yield displacement of the steel core. Six cycles at Ab
were then applied. The remaining protocol was based on the design story
drift of 1% on the prototype structure shown in Fig. 3. For one (1) 16 ft.
(4.88 m) brace in a 13 ft. (3.96 m) by 15 ft. (4.57 m) bay or two (2) 16 ft.
(4.88 m) braces in a 13 ft. (3.96 m) by 30 ft. (9.14 m) bay, 1% story drift
corresponds to a local brace displacement of 1.19 in. (30.23 mm) (Abm).
Four cycles each were applied at deformation levels corresponding to 0.5
Abm, 1.0 Abm, and 1.5 LIbm. Two cycles were applied at 2.0 Abm and higher
deformation levels incremented by 0.5 Abm to failure.
29
3
2.5
2
1.5
0.5
0
C.,
a
.
-0.5
-1
-1.5
-2
-2.5
-3
0
Figure
12:
15
30
45
60
Turn (nm)
75
90
105
120
Increasing amplitude displacement protocol imposed on most
test specimens.
30
Random Displacement History Development
Specimen 50P-2 was subjected to multiple iterations of a random
displacement history derived from nonlinear dynamic time history analysis
of a three-story BRBF building.
The building modeled in this analysis is based on the work of Sabelli
(2000) and the SAC model building design criteria. The building plan
dimensions as shown in Fig. 13 are 124 ft. by 184 ft. with 30 ft. by 30 ft.
bays and a 2 ft. perimeter wall offset. Story heights are a typical 13 ft. The
SFRS consisted of eight BRBFs with four in each orthogonal direction. The
building was designed for a site in metropolitan Los Angeles according to
the 1997 NEHRP Recommended Provisions for Seismic Regulation of New
Buildings and Other Structures (FEMA, 1997) and the 1997 Uniform
Building Code (ICBO, 1997).
For ana'ysis, one BRBF was modeled with an additional single
column representing the secondary P-A load affect attributed to the BRBF.
The horizontal stiffness contribution of this equivalent gravity framing
column was neglected as is standard design practice. The modeled frame
along with member properties is shown in Fig. 14 and Table 4. Threedimensional analysis was not considered given the regular building layout.
Story masses applied to the modeled frame were calculated based
on the total story mass divided by the number of braced frames in a given
31
r--30 ft
_Tm_I__
___
r
30 ft
L
124 ft
184 ft
I
I
I
_______IIJIi{IJIIJIIELi_______ I
___I_I
H
I
Mechanical
Penthouse
__-
Buckling Restrained
Braced Frame
I
[1 Braced Fram
Modeled
Figure 13: Three-story building plan (Sabelli, 2000) used for
time history analysis.
32
l5ft
-I..
15ft
30ft
Figure 14: Three-story BRBF model.
-
Table 4: Three-Story BRBF Model Member Properties
Story
Brace Yield Force
Horiz. Brace
Stiffness
(1)
2
1
117
196
243
(kN)
(2)
BF
Beam
Kh
Py
(kip)
BF
Column
520
872
1081
(kip/in)
588
943
1088
(kN/mm)
(3)
103
165
191
(4)
(5)
Non-BF Columns (Minor Axis)
Side
Interior
Mech.
Perp. BE
(6)
(7)
(8)
(9)
(in4)
W12x96 W14x48 W14x48 W14x61
W14x74 W12x96
(mm4)
(in3)
(mm4)
(10)
(11)
1033 429967063
290 4752249
0)
34
orthogonal direction. Design loads used in these calculations are shown in
Table 5.
At the
roof level
one
half
of the ceiling/flooring
and
mechanical/electrical loads were applied. Seismic masses for each story
are shown in Table 6. Lumped masses were used given that only
horizontal ground motions were considered. Braced frame beam and
column loads were calculated using the load combination 1.2D + 0.5L +
1.OE. The earthquake term was applied in the form of dynamic ground
motion records.
P-A column loads were calculated using the same load
combination and considering 60% live load reduction. Table 6 summarizes
the calculated nodal loads. Braced frame dead and live loads were applied
at third points of the beams where subframing (not explicitly modeled) was
connected to the beams.
Nonlinear dynamic time history analysis was conducted using the
nonlinear structural analysis computer program PC-ANSR (Maison, 1992).
Frame members were modeled using element type 4, a nonlinear beamcolumn
element.
Beams
were
considered
inextensible.
Nodal
displacements within a story were set to be equivalent. This was consistent
with the assumption of rigid diaphragms. Therefore the non-braced frame
beams were not modeled in this analysis. Horizontal stiffness of the P-A
columns was neglected. Connections with gusset plates for brace
attachment were modeled as fixed. The roof beam/column connections
where no braces framed in were considered pinned (simple shear tab). All
35
Table 5: Three-Story Building Design Loads
Unit Weight
(2)
Load
(1)
Dead Loads
Steel Framing
Floor and Roof
Roofing
Ceiling/Flooring
Mechanical/Electrical
Partitions
Exterior Wall
Live Load
As Designed
50 psf 2.3941 kPa
(3 in. Metal Deck with 2 1/2 in. Normal Weight Concrete)
7 psf
0.3352 kPa
3 psf
0.1436 kPa
7 psf
0.3352 kPa
47 psf 2.2505 kPa (At Penthouse)
20 psf
0.9576 kPa (Gravity Design)
10 psf
0.4788 kPa (Seismic Design and Analysis)
25 psf
1.1970 kPa
50 psf
2.3941 kPa
Table 6: Three-Story BRBF Model Loads
Story
(1)
3
2
1
Seismic Mass
(kip-sec2/in) (kN-sec2/mm)
BF Column Load
(kip)
(kN)
(2)
1.0700
1.1915
1.1915
(3)
0.1874
0.2087
0.2087
30.3
50.1
50.1
134.8
222.8
222.8
BE Beam Load
(kip)
(kN)
(4)
12.2
54.4
19.2
85.4
19.2
85.4
P- Column Load
(kip)
(kN)
(5)
410.3
466.4
466.4
1825.0
2074.5
2074.5
36
framing members were ASTM A992 steel, with a strain hardening modulus
5% that of Young's Modulus. Braces were modeled as nonlinear truss
elements (element type 2). ASTM A36 steel was assumed for the braces.
The compressive yield stress was modeled as 110% of the tensile yield
stress based on typical buckling restrained brace test results (Aiken, et al.
2000). Brace cross-sectional area was calculated from the brace yield
force given by Sabelli (2000) and a nominal yield stress of 36 ksi. An
equivalent Young's Modulus was then calculated from this area and the
horizontal brace stiffness. A post-yield slope of 7.5% of the elastic stiffness
was used as calculated from previous UBB testing (Aiken, et al. 2000).
Inherent viscous damping of 5% was assumed per standard practice in the
seismic design of steel structures and was applied as mass and initial
stiffness proportional damping factors.
Ground motions considered (LAOI-LA2O) were developed for the
SAC steel project (Woodward-Clyde Federal Services, 1997). The 20
earthquake records used are for a site in Los Angeles with a 10%
probability of exceedence in 50 years (design basis earthquakes, 475 year
return period). Nonlinear dynamic time history analysis was completed for
the LA series earthquakes and the results analyzed to determine the event
that produced the greatest BRB demand. Of the 20 synthetic earthquake
records, LA2O generated the highest BRB demand in terms of maximum
brace displacement and cumulative ductility. First story compression
37
dominated brace axial displacement time history response for LA2O is
shown in Fig. 15. This displacement history was simplified and scaled to
develop a random displacement history (Fig. 16). In the simplification, large
displacement peak-to-peak displacements were retained and smaller
elastic cycles were neglected. Displacement values were scaled such that
the maximum compressive displacement corresponds to 1% story drift
(1.19 in.
(30.23mm) local brace displacement,
Abm).
The random
displacement history was applied at the same 1.33 in/mm (33.78 mm/mm)
displacement rate as the increasing amplitude displacement history.
Multiple iterations of this random displacement history were applied to
specimen 50P-2. After each iteration both load and displacement were
returned to zero with an additional small inelastic displacement and elastic
unloading.
1.5
)
E
a)
0
0
-0.5
0.
C')
-1.5
-2
10
15
Time (sec)
25
Figure 15: First story BRB axial displacement time history for LA2O.
a)
39
1.5
C
C
w
E
w
0
0
-0.5
(I)
-1.5
-2
0
2
4
6
Tine (nm)
8
10
Figure 16: Simplified random displacement history
imposed on specimen 50 DB-2.
12
EXPERIMENTAL RESULTS
Parameters Used for Comparison
A/SC/S EAOC Recommended Buckling-Restrained Brace Frame
Provisions (AISC/SEAOC, 2001) specify that the ratio of maximum
compressive force to maximum tensile force (C/T) shall not exceed 1.3.
This criterion serves to limit potential unbalanced forces and ensures
reasonably symmetric hysteretic behavior.
BRB demand from the
increasing amplitude displacement protocol defined in the AISC/SEAOC
Provisions is based on nonlinear dynamic time history analysis of BRBF
buildings (Sabelli, 2000).
BRBs are required to achieve displacements
corresponding to 1.5 Abm (mean of Sabelli analysis) and cumulative
ductilities of 140 Aby (mean plus one standard deviation of Sabelli analysis).
These are believed to be conservative values and may be revised as more
data becomes available (AISC/SEAOC, 2001).
Test Observations
Results for all specimens are summarized in Table 7 and shown in
the appendix. Post-test yielding core pictures, load-displacement plot,
displacement plot, string pot displacement plot, yielding core/confining tube
relative displacement plot, and an additional plot illustrating performance
are shown for each specimen. Displacements reported in hystersis and
Table 7: CYD Performance Summary
Max.
Specimen
Tensile
Force
T
(kip)
(kN)
Max.
Compressive
Force
CIT
C
(kip)
(kN)
154.7
688.1
155.8
693.0
163.5
145.8
143.6
167.2
648.5
638.7
743.7
95.5
137.0
143.9
727.2
424.8
609.4
131.9
586.7
131.1
583.1
158.6
159.9
166.2
167.1
705.5
711.2
739.3
743.3
169.6
182.4
257.6
252.9
754.4
811.3
1145.8
1124.9
50DB-i
50DB2
64.6
68.0
287.3
302.5
68.8
78.2
306.0
347.8
1.07
50P1
67.0
57.9
298.0
257.5
73.3
326.0
320.7
1.09
125DB-i
125DB2
125DB3
125DB4
125DB5
125P1
125p2
125P3
125P-4
125P-5
50P-2
(3)
72.1
DB Dog bone configuration
P Perforated configuration
640.1
Tensile
Displacement
(mm)
(in)
(2)
151.6 674.3
(1)
Max.
(4)
1.02
1.05
0.66
0.95
0.86
0.99
1.07
1.14
1.55#
1.51 #
1.15
*
Max.
Compressive
Displacement
(mm)
(in)
(5)
Cumulative
Ductility
(kip-in) (kN-mm)
(by)
(7)
(8)
176
1 @2°bm
183
2 @2.0 Lbm
(6)
2.404
61.06
2.452
2.394
4.177
2.969
2.391
60.81
2.074
52.68
106.10
75.41
60.73
1.705
2.803
2.057
43.31
71.20
52.25
1.269
2.204
2.364
2.408
2.410
32.23
55.98
60.05
61.16
1.038
26.37
42.90
59.49
57.86
1.816
2.356
46.13
59.84
1.804
0.718
45.82
18.24
61.21
Total Energy
Dissipated
62.28
5230
6165
2051
5852
5785
590881
696517
231720
661154
653585
125#
Fracture
On Cycle
(9)
**
272
216
2
1
1525
172293
83 #
4
559812
661832
862822
767355
220
1
53.21
4955
5858
7637
6792
280
236
1.660
42.16
1957
221100
182
2.344
59.54
1230
138964
101 #
1.715
1.223
43.56
31.06
1639
1475
185173
166660
195
180
1.689
2.342
2.278
2.095
261
1st
Compressive
Degradation
On Cycle
(10)
2@ 15bm
2
@ 1.5 Abm
1 @O.SLbm
@ °5bm
@ 1.5
@ 3.OAbm
@ 2.0 'bm
3
@ 1.0 bm
@ 2.0 Lbm
1 @0.5 L\bm
3
1.0 bm
1 @2°brn
**
2
bm
@
2@ l.5Abm
**
3@ l.5Abrn
4@ 1°bm
2@ 15bm
2@ l.SLbm
2@ i.OAbm
Iteration 3
**
**
*
Unequal tensile and compressive displacements
Limit state other than fracture
# Does not meet AISC / SEAOC Provisions
## Compressive Degradation not observed
**
-
42
displacement figures are the CYD yielding core axial displacement based
on weighted average of the east and west yielding core displacement
sensors. The string pot displacements show the east and west yielding
core string pot displacements. A differential displacement of these sensors
provides an indication of out of plane bending of the yielding core outside
the confining tube. The yielding core/confining tube relative displacement
plot shows the relative movement of the yielding core into and out of the
confining tube at each end. Typically the majority of yielding core
displacement took place at the south (actuator) end of the specimen.
Bolt slip was not observed
indicating adequate
slip critical
connection design. Detailing of class A slip surface eliminated the expense
of sand blasted faying surfaces and did not decrease CYD performance.
Yielding was distributed along the entire reduced section yielding
core length for both the dog bone and perforated configurations as
evidenced by uniform flaking of mill scale. Strain gages on the yielding core
did not indicate bending (with the exception of 125DB-3) and showed
equivalent strain at the three instrumented locations up to the 3000
microstrain range limitation of the gages.
The typical failure mechanism observed was fracture of the steel
yielding core induced by increased tensile strains due to local high
amplitude buckling at the actuator end of the specimen. Increasing the
length of unreduced cross-section within the confining tube would provide
increased buckling resistance for this portion of the device. This would
provide a larger unreduced yielding core surface area to be in contact with
the confining media thereby limiting buckling and the associated bending
strains.
Confining Media Effects
CYD performance was determined to be highly dependent on
confining media particle size. 125DB specimens were tested using pea
gravel, sand, 3/4 in. (19.05 mm)to #4 gravel, and 3/4 in. (19.05 mm) minus
gravel.
Specimen 125DB-2 tested with pea gravel confining media provided
reasonably stable
and
symmetric
hysteretic
response.
The
load-
displacement curve for this specimen is shown in Fig. 17. The CIT value of
1.05 is well within the suggested 1.3 limit and in line with a compressive
overstrength of 1.1 typical of UBBs. A total of 6165 kip-in (696517 kN-mm)
of energy was dissipated by the device. The cumulative ductility of 183
exceeded the 140
by
by
requirement of the AISC/SEAOC Provisions.
Pea gravel confining media was also used for specimen 50DB-i.
Fig. 18 shows reasonably stable and symmetric dissipation of 1957 kip-in
(221100 kN-mm) of energy. The C/I value was 1.07 and a cumulative
ductility of 182
Aby
was achieved. The smaller yield force device dissipated
44
2J0
150
100
:°
.
0
-J
-50
-100
-150
I
-3
-2.5
I
-2
-1.5
I
-1
If
-0.5
I
0
0.5
Displacement (in)
1
1.5
Figure 17: Specimen 125DB-2 hysteresis.
2
2.5
3
45
iXJ
75
50
25
0
-J
-
-50
-75
-1W
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
Displacement (in)
Figure 18: Specimen 50DB-i hysteresis.
1.5
2
2.5
proportionally less energy but still achieved approximately the same
cumulative ductility as 125DB-2.
Sand confining media did not adequately prevent the yielding core
(125DB-3) from translating through the confining media. As a result the
core buckled in approximately the fourth mode in the weak direction and
second mode in the strong direction. The load-displacement curve (Fig. 19)
shows this buckling with significant pinching of the hysteresis loops. After
the second cycle at 1.5
bm
a large tension excursion was applied to a
displacement of 4.2 in. (106.7 mm) without yielding core fracture. This
indicates the dog bone yielding core is capable of undergoing significant
inelastic deformation and that the buckling did not produce large strain
concentrations at one particular location along the yielding core. Sand
confining media for this specimen geometry does not provide sufficient
confinement to enable stable and symmetric hysteretic damping.
Larger sized aggregates alone did not significantly enhance
performance. Significant crushing of the 3/4 in. (19.05 mm) to #4 gravel
and the associated confining media volume loss led to considerable
localized buckling at the ends of the reduced section of specimen 125DB-
4. Compressive degradation was observed significantly earlier than with
pea gravel or 3/4 in. (19.05 mm) minus gravel confining media (cycle 3
0.5
&m vs. cycle 2 @ 1.5
bm).
©
3/4 in. (19.05 mm) to #4 gravel is not an
optimal confining media for this specimen geometry.
47
- - - Thc Stiffness
nirYid
150
100
:°
J0
-50
-100
-150
I
-2
-1.5
-1
'I
-0.5
I
I
I
0.5
1
I
I
I
I
I
0
1.5
2
Displacement (in)
25
3
Figure 19: Specimen 125DB-3 hysteresis.
3.5
IJ
4
4.5
Specimen 125DB-5 tested with 3/4 in. (19.05 mm) minus gravel
confining media performed similar to specimen 125DB-2 confined with pea
gravel. The larger aggregate locks together preventing translation with
fines filling voids. No significant benefit was observed by using the 3/4 in.
(19.05 mm) minus gravel. Pea gravel was used as the confining media for
remaining testing and the cost associated with producing the 3/4 in. (19.05
mm) minus gravel blend were avoided.
For all specimens the threaded rods were initially tensioned to
approximately 5 kip (22.2 kN) each to maintain the confining media
volume. This force diminished during testing due to crushing of gravel
confining media and associated volume change. Typically I kip (4.4 kN) of
tension force remained in each threaded rod after testing when the dead
blow hammer was used for compaction. When the pencil vibrator and dead
blow hammer were both used for compaction typically 2 kip (8.9 kN) of
tension force remained in each threaded rod when testing was complete.
This higher retention of rod force can be attributed to increased confining
material relative density when compacted using both methods. With more
confining material contained within the same volume, particle translation is
reduced and localized crushing does not create significant confining media
volume change.
Testing of different confining media indicated that particle size and
shape must be such that localized crushing of the confining media does not
49
create a significant volume loss, and that there is adequate particle
interlock so that the yielding core cannot translate through the confining
media. It is hypothesized that a rectangular confining tube may help to
prevent confining media translation. The rolled corners of a rectangle
section might better lock-in the confining media than the circular shape of a
pipe.
Perforation Blocking Effects
Specimen 125P-1 was tested with perforations filled with spray foam
to prevent the yielding core perforation ends from bearing on the pea
gravel
confining
media.
Desirable
structural
performance was not
achieved. Fig. 20 shows a lack of stable hysteresis due to the legs of the
first perforation at the actuator end buckling in towards each other. Abrupt
stiffening occurred when the buckled legs came into contact with each
other.
Following the poor performance of specimen 125P-1, different
configurations of perforation blocking were investigated to prevent buckling
of perforation legs. Combinations in which the complete width of the first
two perforations on each end and partial width (perforation width minus 1/2
in.) of the remaining perforations were blocked with steel plate provided the
50
- - - - Therc StifFness
nrYid
I
Ij
.
0
-J
-
-15:
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
Displacement (in)
Figure 20: Specimen 125P-1 hysteresis.
2
2.5
3
51
best results. It is possible that perforation blocking could be completely
avoided by using shorter perforation leg lengths, while still achieving
required ductility.
Reasonably stable and symmetric hysteretic behavior is shown in
Fig. 21, for specimen 125P-5. The first two perforations at each end were
completely blocked with their original knockout from water jet cutting.
Remaining perforations were blocked with a plate 2 in. (50.8 mm) shorter
and 1/2 in. (12.7 mm) narrower than the perforation dimensions. The
elastic compressive stiffness for this blocked configuration was 845 kip/in
(148 kNlmm), which was 1.45 times greater than the compression stiffness
with no perforation blocking. This accounts for the compressive stiffening
observed in the hysteresis curve. Perforation blocking did not affect tensile
stiffness. The CIT value of 1.51 is above the AISC/SEAOC 1.3 limit. Future
detailing of shorter legs would eliminate the need for perforation blocking
and the associated compressive stiffening (high CIT value). A total of 6792
kip-in (696517 kN-mm) of energy was dissipated by the device. A
cumulative ductility of 236
by
was achieved before testing was suspended
to limit damage to the reaction system from the high compressive forces.
Specimen 50P-1 was tested with the first two perforations at each
end blocked with a steel plate I in. (25.4 mm) shorter and equal in width to
the peroration dimension. Remaining perforations were blocked with a
plate 1 in. (25.4 mm) shorter and 1/2 in. (12.7 mm) narrower than the
52
200
1
100
a
0
_J
-lEAD
n
-200
-2EAD
U
I
-3
-2.5
I
-2
I
-1.5
I
-1
I
-0.5
0
0.5
1
1.5
Displacement (in)
Figure 21: Specimen 125P-5 hysteresis.
2
2.5
3
53
perforation dimensions. The hysteresis curve (Fig. 22) indicates reasonably
stable and symmetric hysteretic damping. Compressive stiffening observed
in specimen 1 25P-5 was eliminated by not blocking the full length of the
two perforations at each end. The weak direction of each perforation leg
was in the out of plane direction. Buckling observed was in the out of plane
direction and thus not restrained by perforation blocking. 1639 kip-in
(185173 kN-mm) of energy was dissipated by the device. The CIT value
was 1.09 and a cumulative ductility of 195
by
was achieved. The smaller
yield force device dissipated proportionally less energy but still achieved
approximately the same cumulative ductility as 125P-5.
Decreasing Amplitude Displacement History
A decreasing amplitude displacement history was applied to
specimen 5ODB-2. One cycle at 2.0
bm
was followed by two cycles at 1.5
bm
Yielding core fracture was observed on the subsequent cycle at 1.0
bm
The energy dissipated and cumulative ductility were 1230 kip-in
(138964 kN-mm) and 101
Aby,
those of specimen 50DB-i
respectively. These values are less than
subjected to the
increasing amplitude
displacement protocol. However the largest single excursion displacement
was 0.5 Abm larger for specimen 5ODB-2. This provides an indication that
device performance is dependent on applied displacement history and
devices can sustain very large cycles.
54
icx
Ii
7550
0
-J
-
-50
-75
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
Displacement (in)
Figure 22: Specimen 50P-1 hysteresis.
1.5
2
2.5
55
Random Displacement History
Specimen 50P-2 was subjected to a random displacement history
as defined above. Seven complete iterations of the random displacement
and an eighth iteration up to the point of maximum compressive
displacement were applied. Loading was suspended at maximum
compressive displacement to examine the yielding core in that state.
Confining media and the yielding core were removed from the confining
tube. The yielding core was inspected for damage resulting from the
applied random displacement history. A new yielding core and confining
media could have been placed back into the confining tube and the device
reinstalled for subsequent testing. Buckling and compressive stiffening was
observed in the hysteresis curve (Fig. 23). Local buckling of the yielding
core against the side of the confining tube resulted in this post-buckling
compressive stiffening. Fig. 24 presents each individual iteration of random
displacement history and shows progressive degradation in
CYD
performance. There was a gradual decrease in the energy dissipated per
iteration (Table 8) due to pinching of the hysteresis loops. Cumulative
ductility values per iteration however do not illustrate this performance
degradation because the same displacements were reached but at lower
brace
axial
forces.
Therefore
cumulative
ductility
performance
specifications should be combined with other measures to ensure
reasonably stable and symmetric hysteretic response, such as efficiency of
1(X)
75
50
25
.
0
0
-I
-50
-75
-100
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
Displacement (in)
Figure 23: Specimen 50P-2 hysteresis.
1.5
2
2.5
Iteration I
Iteration 2
a
a
25
0
a
it
-J
-J
0
0
-25
-1
-55
0
Dlsplacennt (in)
05
1
IS
-15
-1
-05
Iteration 3
a
0
Displacenent (In)
0.5
I
IS
1
15
Iteration 4
25
a
0
0
-j
-I
.25
-w
-15
-1
45
0
Dlsplacermnt (In)
05
1
1.5
-1
45
Iteration 5
0
Dlsplacenwnt (In)
05
Iteration 6
a
0
0.
a
0
25
0
-J
-j
-15
-1
-0.5
0
Displacenent (In)
0.5
I
15
.15
-1
Iteration 7
0
-0.5
pacenent (In)
55
I
15
Iteration 8
a
a'
0
a
0
-J
I
Displacenent (In)
1.5
l3.l
45
0O.5
Displacenent (In)
1
Figure 24: Specimen 50P-2 hysteresis for each iteration of imposed
random displacement history.
I.5
Table 8: Random Displacement History Iteration Comparison
Iteration
T
Max. Tensile
Force
(kip)
(1)
1
2
3
4
5
6
7
8
(kN)
Max. Compressive
Force
(kip)
(2)
56.4
53.8
56.9
57.9
57.6
57.2
55.8
54.3
65.1
72.1
253.1
70.0
257.7
65.5
63.0
62.0
58.4
58.4
256.1
254.3
248.0
241.4
(kN)
289.4
320.9
311.5
291.3
280.3
275.9
259.7
259.6
(mm)
(in)
(4)
(3)
250.8
239.3
Max. Tensile
Displacement
.
CIT
1.15
1.34
1.23
1.13
1.09
1.09
1.05
1.08
Max. Compressive
Displacement
(in)
(5)
0.718
0.719
0.724
0.726
0.727
0.727
0.692
0.698
(mm)
Total Energy
Dissipated
(kip-in)
(6)
18.24
18.26
18.39
18.44
18.47
18.47
17.58
17.73
1.176
1.186
1.185
1.188
1.183
1.186
1.149
1.132
I
(kN-mm)
230
223
211
196
186
179
159
90
1475
I
(Aby)
(8)
(7)
29.87
30.12
30.10
30.18
30.05
30.12
29.18
28.75
Total
Cumulative
Ductility
26039
25186
23891
22134
20990
20233
18019
10167
166660
24.0
24.6
24.3
24.3
24.4
24.5
22.8
11.5
180.4
59
energy dissipation or secant stiffness on subsequent cycles of similar
amplitude.
The experimental results were then compared with a PC-ANSR time
history response for a CYD subjected to the imposed random displacement
history. The original properties for the inelastic truss element used to model
the brace were a compressive yield strength equal to 1.1 times the tensile
yield strength; an effective Young's Modulus calculated from brace
stiffness, length, and cross-sectional area; and a strain hardening modulus
of 7.5% of Young's Modulus. These are the same brace properties used in
the three-story building model to generate the time history response.
When compared to actual CYD performance it was determined that a
compressive yield strength equal to the tensile yield strength more
accurately reflected experimental results. Also an efficiency factor of 80%
was applied to Young's Modulus to better represent elastic CYD stiffness.
The strain hardening modulus was divided by this efficiency factor to
maintain the same post yield slope. Experimental and analytical results are
illustrated in Fig. 25. The energy dissipated by specimen 50P-2 iteration 2
was 223 kip-in (25186 kN-mm) while the analytical model dissipated 170
kip-in (19206 kN-mm). The analytical model therefore conservatively
underestimates the energy dissipation capacity of the CYD.
The response of the model three-story building was then determined
with the revised CYD properties to determine if the developed random
ico
75
Smai 50P-2 (ec 2)
PCANSR
50
25
D
0
J
0
-
II
-1.5
-1
-0.5
0
Displacement (in)
0.5
1
1.5
Figure 25: Experimental and analytical force-deformation response for
specimen 50P-2 during second iteration of imposed random
displacement history.
61
displacement history was still an accurate representation of expected BRB
demand. First story BRB time history response (Fig. 26) for the initial and
revised cases show a 16% increase in maximum brace axial displacement.
Roof displacement increased by 14% for the revised BRB properties as
shown in Fig. 27. Residual displacements also increased as given in Table
9. This increase in displacements would not significantly change overall
BRB ductility demand during the event.
1.5
-
IritiBraePrcües
-. Fisei Brace Prqeres
O.5
0)
E
0)
a
I:
-1.5
2.5
-3
0
5
10
15
Time (sec)
2.)
25
30
Figure 26: Analytically predicted BRB axial displacement in the first story
time history using theoretical CYD response and modified based on
experimental results.
[;]
10
-
8
H_____
6
C
w
E
IritiBraePrcçes
-. Revised Brace Prcçes
4
C.)
Cu
a.
U)
1\
9.-
0
0
-2
-4
10
15
Time (sec)
2)
25
30
Figure 27: Analytically predicted roof displacement time history using
theoretical CYD response and modified based on experimental results.
Table 9: Nonlinear Dynamic Time History Results
Element
(1)
Local Brace
Horizontal Roof
Initial Brace Properties
Max. Displacement Residual Displacement
(in)
(mm)
(in)
(mm)
.
(2)
2.57
7.94
(3)
65.28
201.68
0.72
0.99
18.29
25.15
Revised Brace Properties
Max. Displacement Residual Displacement
(in)
(mm)
(in)
(mm)
(4)
2.97
9.03
(5)
75.44
229.36
0.96
1.34
24.38
34.04
65
CONCLUSIONS
A new type of tension-compression yielding brace or bucklingrestrained brace to dissipate seismic induced forces has been investigated
and tested. The Confined Yielding Damper consists of a steel yielding core
element within a structural tube filled with non-cohesive media. This non-
cohesive media is placed under a normal confining force to provide
buckling resistance of the core, enabling the device to yield in compression
without global buckling of the brace. The testing program examined the
effects of different confining media, perforation blocking configurations, and
random displacement histories. Based on Confined Yielding Dampers test
results the following observations and conclusions are presented:
1. A properly designed, detailed, and constructed CYD device exhibits
reasonably stable and symmetric hysteretic response of input fully
reversed cyclic loading.
2. Bolt slip was avoided with slip-critical bolted connections, class A
slip surfaces, and fully tensioned A490 high strength structural bolts.
3. Extending the unreduced length of steel yielding core further into the
confining tube would help to reduce local buckling at the end of the
yielding core by providing more rotational and translation resistance.
4. Confining media particle size and shape must be such that localized
crushing of the confining media does not create a significant volume
loss.
5. Confining media particle size and shape must be such that there is
adequate particle interlock to limit yielding core translation through
the confining media.
6. Reducing the perforation leg length would increase the perforation
buckling capacity and limit the necessity for perforation blocking.
7. Gradual compressive degradation was observed when a CYD was
subjected to multiple iterations of a random displacement history,
although the performance as measured by cumulative ductility or
energy dissipation was quite good even after the 6th iteration.
8. CYDs can be uninstalled, inspected, reconstructed, and reinstalled
after a seismic event while reusing major components of the device.
9. Cumulative ductility performance specifications should consider
other quantitative measures to ensure reasonably stable and
symmetric hysteretic response for all types of yielding dampers.
Change in energy dissipation or secant stiffness on subsequent
cycles of similar amplitude would provide an additional indication of
device performance.
10. The cross-sectional area and mechanical properties of the yielding
core can be tailored to provide a device with the desired strength,
stiffness, and yield surface properties. Use of the perforated
configuration provides greater flexibility in design.
11. The CYD can provide performance similar to that of the UBB, but
has the additional benefits of reduced cost, post event inspection,
simplified design, detailing, and construction.
The Confined Yielding Damper may provide a cost effective passive
energy dissipation option that builds upon the strengths of the UBB.
Desired structural performance properties of the CYD can be achieved by
varying the cross-sectional area and mechanical properties of the steel
core. Strength, stiffness, and yield surface properties can be adjusted
using different grades of steel and different geometry of the steel core
element. Multiple plates, of the same or different material, combined in
parallel would permit further refinement of the design performance of the
CYD device facilitating achievement of performance based design
objectives. Additional testing of configurations of perforations, confining
tube geometry, and confinement would aid future development of this type
of damper.
BIBLIOGRAPHY
American Institute of Steel Construction. (1993). "Load and Resistance
Factor Design Specification for Structural Steel Buildings." Chicago,
Illinois.
American Institute of Steel Construction I Structural Engineers Association
of California. (2001). "Recommended Buckling-Restrained Braced
Frame Code Provisions (Draft)."
Applied Technology Council. (1992). ATC-24. "Guidelines for Cyclic
Seismic Testing of Components of Steel Structures." Redwood City,
California.
Aiken, I., Clark, P., Tajirian, F., Kasai, K., Kimura, I., Ko, E. (2000).
"Unbonded Braces in the United States-Design Studies, Large-Scale
Testing and the First Building Application." Proceedings of International
Symposium on Passive Control, Tokyo Institute of Technology, Tokyo,
Japan. pp. 203-21 7.
Black, C., Makris, N., Aiken, I. (2002). "Component Testing, Stability
Analysis and Characterization of Buckling Restrained Braces." Final
Report to Nippon Steel Corporation, Tokyo, Japan.
Federal Emergency Management Agency (1997). "1997 Edition NEHRP
Recommended Provisions for Seismic Regulation of New Buildings and
Other Structures." Washington, D.C.
Higgins, C. and Newell, J., "Development of Two New Hysteretic
Dampers," Proceedings of the Seventh U.S. National Conference on
Earthquake Engineering, Boston, Massachusetts, July 2002.
Higgins, C. and Newell, J., "Development of Economical Hysteretic
Dampers," Proceedings of the International Symposium on Passive
Control, Tokyo Institute of Technology, Tokyo, Japan, December, 2001.
International Conference of Building Officials. (1997). "Uniform Building
Code." Whittier, California.
BIBLIOGRAPHY (Continued)
Maison,
B.
(1992). "PC-ANSR A Computer Program for Nonlinear
Structural Analysis." University of California, Berkley, California.
Research Council on Structural Connections. (1994). "Specification for
Structural Joints Using ASTM A325 or A490 Bolts." Chicago, Illinois.
Sabelli, R. (2000). "Research of Improving the Design and Analysis of
Earthquake-Resistant
Steel-Braced
Frames."
2000
Professional Fellowship Report, E E RI, Oakland, California.
NEHRP
Watanabe, A. (1992). "Development of Composite Brace with a Large
Ductility." US-Japan Workshop on Composite and Hybrid Structures,
San Francisco, California.
Watanabe, A., Hitomi, Y., Saeki, E., Wada, A., Fujimoto, M. (1988).
"Properties of Brace Encased in Buckling-Restraining Concrete and
Steel Tube." Proceedings of Ninth World Conference on Earthquake
Engineering, Tokyo-Kyoto, Japan. Paper No. 6-7-4. Vol. IV, pp. 719-
724.
Woodwa rd-Clyde Federal Services. (1997). "Draft Report: Develop Suites
of Time Histories." Report to SAC Joint Venture Steel Project.
Pasadena, California.
70
APPENDIX
72
3----
2.5
C
C
E
0)
0.
11)
0
10
)
30
40
50
60
70
80
Time (mm)
)
100
110
IZ)
130
140
150
Figure A3: Specimen 125DB-I Displacement
3
2.5
- - - -. EtStnngPct
VstSüirigPct
2
C
1.5
1
C
0)
0.5
E
0)
0
C.)
0.
U)
-0.5
-1
-1.5
-2
-25
.1
o
io
30
40
50
60
70
80
Time (mm)
)
100
110 1) 130
Figure A4: Specimen 125DB-i String Pot Displacement
140
150
73
4
3.5
Dsaeiiait-S
3
.
Z5
C)
2
C)
1.5
E
(.)
I'
I,
1
60 E
0.5
C)
-0.5
-1
II
-1.5
U,
>
0
------
-2
-2.5
C)
-3.5
-4
0
a)
10
40
30
60
50
70
80
Time (mm)
9)
100
110
120
130
140
150
Figure A5: Specimen 125DB-i
Yielding Core/Confining Tube Relative Displacement
5
-
TiTeaJed Rxl Lcal E
II
I
0
-J
0
_
II
_______
/a
lIalp...Z
__
au
I
E
,
Ii
I
I
4
Ia
I
I
Ii
I
a
UI
II
;.
I
r_j
"l.
a.
/lls
I
4
II
,,s'.s
I_
.
10
20
30
40
50
60
70
8)
Time (mm)
9)
100
110
12)
13)
Figure A6: Specimen 125DB-i Threaded Rod Load
140
150
75
3
2.5
C
E
0)
U)
OIIIIIIHhuIIII
0
10
)
30
40
50
30
70
30
1(X)
X)
Time (mm)
110
120
130
140
150
130
140
150
Figure A9: Specimen 125DB-2 Displacement
3
- - - -. EtStnrPc
2.5
VstSUingPct
2
I
1.5
1
4-I
C
0)
E
0)
U
0.
U)
0.5
0
-0.5
-1
-1.5
ml
-2
-2.5
0
10
20
30
40
50
30
70
80
Time (mm)
)
1(X)
110
120
Figure AlO: Specimen 125DB-2 String Pot Displacement
4
3.5
3
25
0)
- - - -. IisØaana1-N
Dspaaiiit- S
2
0)
0
-
0.5
0)
-0.5
U)
0
-1
U)
>
0
C,
-25
-3.5
-t
0
10
Z)
30
40
60
60
7o
ao
Time (mm)
1(X)
110
120
130
140
150
Figure Al 1: Specimen 1 25DB-2
Yielding Core/Confining Tube Relative Displacement
I
i5o1
0
I
10
20
30
40
50
60
70
80
Time (mm)
90
1(X)
110
12)
130
140
Figure Al2: Specimen 125DB-2 Confining Tube Axial Load
I
15)
4.5
4
3.5
a)
E
C)
0
U)
-
0
10
)
30
40
50
50
) 93
Time (mm)
70
1(X)
110
1) 130
140
150
140
150
Figure Al 5: Specimen 1 25DB-3 Displacement
5
- - - -. EtSthrPct
4.5
stStnrPct
4
3.5
3
C
25
C,
2
C,
1.5
U)
0.5
E
0
0
0
-0.5
-1.5
0
10
20
30
40
50
60
70
80
Time (mm)
90
1(X)
110
12)
130
Figure A16: Specimen 125DB-3 String Pot Displacement
79
- - - -. DsØaiiit-N
Dsçaait-S
C
C
E
a3
62
0
.0
1-0
>C,)
0
II
-2
C)
0
10
20
30
40
50
80
70
-
80
Time (mm)
9)
100
110
120
130
140
150
Figure A17: Specimen 125DB-3
Yielding Core/Confining Tube Relative Displacement
r
zcxx
1,500
C
i,co
500
0
.2
-500
-1,(X)
-1,500
-2,000
-spI
!i.!ë!1
I'urtgrs_________
--I-___
. i-vY.I
0
10
2)
3)
Time (mm)
40
50
80
Figure A18: Specimen 125DB-3 Yielding Core Strain Gages D-G3, 4
3
2.5
2
1.5
I
uiuiiiiiuiiiiiuiiiiiiii
?!IJIILIiiIIIIIIIIIIJLPJJIU!IiIPiIlII11
1&&U[1I1I1II1I1 1111111 II 11111 IIIIi
SIitII!I!lI!II!I!IUIIIIIIIIII
iii iriiiu
I
I
.I
S
-
3
2.5
2
1.5
1
E
0
a
I
S
;s
A
i
;s
s
is
:
-
.s
i
-
I
1
-
aiuiiiiiiuiiiu
RMLII1IiIIIiIII1III
IIInIII1IUI!I1i1IIIIII1iiIIIUIII
-1
-1.5
-2
IHhIii1Ii1IitiiI
M.N.IIiiI!r1I,11IUIt1tIII
I
-2.5
-
0
10
-
2)
30
40
50
-
60
70
60
Time (mm)
9)
1CX)
110
12)
130
Figure A22: Specimen I 25DB-4 String Pot Displacement
140
150
4
- --I
3.5
3
C
E
U)
.0
IU)
>
0
0
2.5
2
1.5
irniiiviuiiuiiiu
IUWLIiWIII1&I1IIIii
0.5
0
-0.5
-1.5
-2
-2.5
-3
-3.5
-
0
10
20
30
40
50
50
70
80
Time (mm)
9)
1(X)
110
12)
--
130
140
150
Figure A23: Specimen 125DB-4
Yielding Core/Confining Tube Relative Displacement
I,
I,
I,
C
'I
U)
2
0
II
..II
'I
H
I----
aaiiuriiiiiiimiiiiu
uusuauuui
iii iii in in u
wwuuuuuiiuuiiiiiiiriu
S.
I
0
10
I
2)
30
40
I
50
I
I
60
70
I
I
80
9)
Time (mm)
I
1W 110
II
12)
UI
130
IJ
140
150
Figure A24: Specimen 125DB-4 Confining Tube Strain Gages N-I, B
3
2.5
2
1.5
____.. - _
iiriiiiiniiiiiiiiiim
__i1I!IIIiIIflI!I
IIII
....amiii!iI!it1....
I
41
1
1
A
3
I
l
I
I
-
$
9
II
Al
I
Ii. -
1
1
-
EtSthn3Pct
2.5
\stSthrPct
2
I
1.5
1
E
0.5
U
.!
-1
-1.5
p
-2
-2.5
010
)
334050507050
Time (in)
)1(X)1101)13)140150
Figure A28: Specimen 125DB-5 String Pot Displacement
85
4
3.5
-
3
Isiaanent-N
-
-
Ds1aaTlent-S
W2--------E
0)
C.)
15-------------------4--'-------------r 1-.
II
?
.i
i
I
I
-2
o
0
0
10
)
30
40
50
60
70
80
Time (mm)
9)
100
110
1Z)
130
140
150
Figure A29: Specimen 125DB-5
Yielding Core/Confining Tube Relative Displacement
500
TiteSGS-E
TitSGS-W
400
-------
100
I
0
10
20
30
40
50
60
70
80
Time (mm)
90
100
110
12)
130
140
150
Figure A30: Specimen 125DB-5 Confining Tube Strain Gages S-E, W
32-
2.5
C,
E
U
0
U)
0
10
20
30
40
50
60
70
80
)
Time (mm)
100
110
12)
130
140
150
Figure A33: Specimen 125P-1 Displacement
3
2.5
H
I----EtSthP
\stSthngPc
2
-
1.5
1
a,
E
C,
0.5
0
C.)
aU)
-0.5
-1
-1.5
-2
-2.5
0
10
2)
30
40
50
60
70
80
Time (mm)
9)
100
110
12)
130
Figure A34: Specimen 125P-1 String Pot Displacement
140
150
4
;
a5
-- - -. Dsaaa1-N
3
Dsp1aeneit-S
---------------
25
G'
2
,
1.5
E
C.,
60
1
0.5
a
-0.5
-1
-i.s
>
U,
0
0
-2
-2.5
-3.5
A
0
10
2)
30
40
50
60
70
80
Time (mm)
)
100
110
130
12)
140
150
Figure A35: Specimen 125P-1
Yielding Core/Confining Tube Relative Displacement
1(X)
Sp.SGAL1
75
Sp. SG A Leg 2
50
25
.
0
0
-J
-25
-50
-75
-1CX) '
0
I
I
I
I
10
20
30
Time (mm)
40
50
I
60
Figure A36: Specimen I 25P-I Yielding Core Load, Location A-Leg 1, 2
3---------------------2.5
a)
E
0)
C)
U)
IIIIIu!Iiu!IIII
0
10
20
30
40
50
60
70
80
)
100
110
Time (mm)
120
130
140
150
Figure A39: Specimen 125P-2 Displacement
3
2.5
2
-
1.5
- --_._._..
-_______....
M!lLitiiiil
I
0.5
E
!IILLLRII1I [II wiiiiniiii
C.,
0.
.!IZ
-1
-1.5
-2
-2.5
0
10
2)
30
40
50
60
70
80
Time (mm)
93
100
110
120
13)
Figure A40: Specimen 125P-2 String Pot Displacement
140
150
91
4
3.5
3
- - - -. DsçAaenal-N
Dspaanel- S
25
G)
E
G)
U
2
1.5
6° ==
0.5
w
.0
>
U)
0
0
-0.5
-1
-1.5
-2
-2.5
-a5
A
0
10
20
30
40
50
50
50
70
)
1(X)
110
120
130
140
150
Time (mm)
Figure A41: Specimen 125P-2
Yielding Core/Confining Tube Relative Displacement
1(X
- - - -. Spec.SGALs1
75
Sp. SG A Leg 2
50
25
D
0
-J
0
-25
-50
-75
-1(X)'
0
I
I
I
10
2)
30
Time (mm)
40
50
I
60
Figure A42: Specimen 125P-2 Yielding Core Load, Location A-Leg 1, 2
93
a,
E
C,
0
U)
0
3
2.5
10
20
30
40
50
60
70
80
9)
I
100
110
120
130
140
120
130
140
Time (mm)
Figure A45: Specimen 125P-3 Displacement
150
- - - -. EtSthrPct
VstSthrPc
2
I
I
1.5
1
a,
E
C)
0
U)
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0
10
20
30
40
50
60
70
80
Time (mm)
9)
1(X)
110
Figure A46: Specimen I 25P-3 String Pot Displacement
150
4
3.5
- -
C)
E
U
-
Dsplaeit-N
siaat-S
3
-
2
1.5
6°
1
0.5
-----------.
-1
,
II
':
(I)
-1.5
>
-2
E
-2.5
0
4I
I
I
SI
I,
c_)
-3.5
-t
0
10
20
30
40
50
60
70
60
Time (mm)
9)
1(X)
110
12)
130
140
150
Figure A47: Specimen I 25P-3
Yielding Core/Confining Tube Relative Displacement
500
- - - -. Tt.tSGN-E
400
Ti±e SG N-W
300
200
Uioo
-200
-3(X)
-400
0
10
20
30
40
50
60
70
80
Time (mm)
90
1(X)
110
12)
130
140
15)
Figure A48: Specimen 125P-3 Confining Tube Strain Gages N-E, W
G)
E
U
O
a.
U)
flT
VUaU
aiiiiiirnuiiiiioiia
UiLJiI1J!I1JIIiIiIillhIU
muuuriii
i
