Design, Construction, and Characterization of a Large Scale Steel Structural... Real Time Hybrid Testing

Design, Construction, and Characterization of a Large Scale Steel Structural... Real Time Hybrid Testing
Design, Construction, and Characterization of a Large Scale Steel Structural System for
Real Time Hybrid Testing
By
Ryan Ahn
A Thesis
Presented to the Graduate and Research Committee
of Lehigh University
in Candidacy for the Degree of
Master of Science
in
Structural Engineering
Lehigh University
August, 2012
This thesis is accepted and approved in partial fulfillment for the requirements of
the Master of Science.
________________________
Date
________________________
Dr. James M. Ricles
Thesis Advisor
________________________
Dr. Richard Sause
Thesis Advisor
_______________________
Dr. Sibel Pamukcu
Department Chair
Department of Civil and
Environmental Engineering
ii
Acknowledgements
The research presented herein is based on work supported by the National Science
Foundation under Award Numbers CMS-1011534 and CMS-0420974, within the George
E. Brown, Jr. Network for Earthquake Engineering Simulation Research (NEESR)
program. Support for the experiments was also provided through NSF Award No. CMS0402490 NEES Consortium Operation. Additional funding for this research was provided
by the Pennsylvania Infrastructure Technology Alliance (PITA), which is funded by a
grant from the Pennsylvania Department of Community and Economic Development (PA
DCED).
The research was conducted at the NEES Real-Time Multi-Directional (RTMD)
Earthquake Simulation Facility located in the Advanced Technology for Large Structural
Systems (ATLSS) Engineering Research Center at Lehigh University. The facility is
affiliated with the Lehigh University Department of Civil and Environmental
Engineering, Dr. Sibel Pamukcu, Department Chair.
I would like to thank Dr. James M. Ricles and Dr. Richard Sause, thesis advisors, for
their guidance and for the opportunity to work on this project. Thank you to my fellow
student researchers especially Dr. Yunbyeong Chae, Research Scientist and Akbar
Mahvashmohammadi and Baiping Dong, Ph.D. candidates, for their help in
understanding dampers. Thank you to the entire ATLSS staff, especially current lab
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foreman Darrick Fritchman and former lab foreman John Hoffner for their guidance in
the sometimes complicated process of design and constructing a large scale test setup and
Thomas Marullo and Gary Novak for assisting me in running experiments. I would also
like to recognize the following ATLSS staff members for their help, including Joe
Griffiths, Russ Longenbach, Jeff Sampson, Adam Kline, Roger Moyer, and Todd
Anthony.
Finally, a special thanks to my family for their support and guidance in all my endeavors.
Without them, this would not have been possible.
iv
Contents
1
Abstract ............................................................................................................................... 1
2
Introduction......................................................................................................................... 3
1.1
1.2
1.3
OVERVIEW .........................................................................................................................................3
OBJECTIVE .........................................................................................................................................4
SCOPE OF THESIS ................................................................................................................................4
3
Background ......................................................................................................................... 6
2.1
2.2
2.3
2.4
GENERAL ...........................................................................................................................................6
SUPPLEMENTAL DAMPING SYSTEMS...................................................................................................6
SIMPLIFIED DESIGN PROCEDURE ........................................................................................................8
PROTOTYPE STRUCTURE ....................................................................................................................9
4
Design of Test Structure ................................................................................................... 18
3.1 GENERAL ......................................................................................................................................... 18
3.2 MRF DESIGN AND LAYOUT .............................................................................................................. 19
3.2.1
Beam-to-column connections ................................................................................................ 19
3.3 MRF DETAILS .................................................................................................................................. 21
3.3.1
Weld Access Holes ................................................................................................................. 21
3.3.2
Panel Zone Design ................................................................................................................ 22
3.3.3
Doubler Plates ....................................................................................................................... 23
3.3.4
Weld criteria .......................................................................................................................... 25
3.4 DBF DESIGN AND LAYOUT ............................................................................................................... 25
5
Experimental Setup ........................................................................................................... 42
4.1 GENERAL ......................................................................................................................................... 42
4.2 FABRICATION AND ERECTION .......................................................................................................... 42
4.2.1
Measured section properties ................................................................................................. 42
4.2.2
DBF fabrication..................................................................................................................... 43
4.2.3
MRF fabrication .................................................................................................................... 43
4.3 LOADING SYSTEM ............................................................................................................................ 46
4.3.1
DBF loading system .............................................................................................................. 46
4.3.2
MRF loading system .............................................................................................................. 47
4.4 BRACING OF TEST STRUCTURE ......................................................................................................... 48
4.4.1
Bracing frame ........................................................................................................................ 48
4.4.2
Loading beam bracing ........................................................................................................... 49
4.4.3
DBF lateral bracing .............................................................................................................. 49
4.4.4
MRF lateral bracing .............................................................................................................. 50
4.5 EXTERNAL REACTIONS..................................................................................................................... 50
4.5.1
Ground links .......................................................................................................................... 50
4.5.2
Bay link .................................................................................................................................. 51
4.6 RIGID LINKS .................................................................................................................................... 51
6
Instrumentation ................................................................................................................. 95
5.1 GENERAL ......................................................................................................................................... 95
5.2 DESCRIPTION OF INSTRUMENTS ....................................................................................................... 95
5.2.1
Internal full bridge load cells ................................................................................................ 95
5.2.2
Full bridge calibration .......................................................................................................... 97
5.2.3
Load cells and load pins ........................................................................................................ 99
5.2.4
Displacement transducers ................................................................................................... 100
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5.2.5
Strain gauges ....................................................................................................................... 104
5.2.6
Accelerometers .................................................................................................................... 105
5.3 DETERMINATION OF INTERNAL FORCE FROM INSTRUMENTATION ................................................. 105
5.3.1
Column and brace shears .................................................................................................... 105
5.3.2
Beam internal forces............................................................................................................ 106
5.3.3
Story shear ........................................................................................................................... 107
5.3.4
Friction on test structure ..................................................................................................... 107
5.4 CALIBRATION OF THE BAY LINK FULL BRIDGE ............................................................................. 108
7
Damped Brace Frame Characterization Testing ............................................................. 141
6.1 GENERAL ....................................................................................................................................... 141
6.2 TESTING METHODOLOGIES ............................................................................................................ 141
6.2.1
Quasi-static testing .............................................................................................................. 141
6.2.2
Sinusoidal tests .................................................................................................................... 143
6.3 FRICTION FORCE ASSESSMENT ...................................................................................................... 143
6.4 DBF STIFFNESS MATRIX ............................................................................................................... 144
6.4.1
Development of stiffness matrix ........................................................................................... 144
6.5 EVALUATION AND MODIFICATION OF FRAME COMPONENTS ......................................................... 146
6.5.1
T-section connection modifications ..................................................................................... 146
6.5.2
Tightening of rigid link bolts ............................................................................................... 147
6.5.3
Ground links ........................................................................................................................ 147
6.5.4
Bay link ................................................................................................................................ 148
6.6 APPLICATION OF STIFFNESS MATRIX FOR REAL-TIME HYBRID SIMULATION ................................. 148
8
Summary, Conclusions and Recommendations .............................................................. 173
7.1
7.2
7.3
SUMMARY...................................................................................................................................... 173
CONCLUSIONS ................................................................................................................................ 174
RECOMMENDATIONS...................................................................................................................... 175
9
References....................................................................................................................... 177
10 Appendix......................................................................................................................... 180
MRF WELD INSPECTION REPORT ............................................................................................................ 180
11 VITA ............................................................................................................................... 181
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Tables
TABLE 3.1 - MRF TEST STRUCTURE DESIGN LOADS ..................................................................................... 27
TABLE 3.2 - MRF MEMBER SIZES .................................................................................................................. 27
TABLE 3.3 – 0.6 SCALE TEST STRUCTURE RBS DIMENSIONS......................................................................... 28
TABLE 3.4 – 0.6 SCALE TEST STRUCTURE CONTINUITY PLATE SIZES ............................................................ 28
TABLE 3.5 - 0.6 SCALE TEST STRUCTURE DOUBLER PLATE SIZES ................................................................. 29
TABLE 3.6 - DBF MEMBER SIZES................................................................................................................... 29
TABLE 3.7 – 0.6 SCALE TEST STRUCTURE DBF COMPONENTS ...................................................................... 29
TABLE 4.1 - AVERAGE MEASURED DBF WF SECTION DIMENSIONS AND COMPUTED SECTION PROPERTIES
(FIGURE ADAPTED FROM LEWIS 2004) .................................................................................................. 53
TABLE 4.2 - AVERAGE MEASURED MRF MEMBER DIMENSIONS AND COMPUTED SECTION PROPERTIES (FIGURE
ADAPTED FROM LEWIS 2004)................................................................................................................ 54
TABLE 4.3 - HYDRAULIC ACTUATOR SPECIFICATIONS (RTMD 2012) ............................................................ 55
TABLE 5.1 – FULL BRIDGE INPUTS ................................................................................................................ 109
TABLE 6.1– STATIC TESTING APPLIED LOADS ............................................................................................. 150
TABLE 6.2 – QUASI-STATIC TEST MATRIX ................................................................................................... 151
TABLE 6.3 – SINUSOIDAL TESTS APPLIED DISPLACEMENTS ......................................................................... 153
TABLE 6.4 – SINUSOIDAL TEST MATRIX ...................................................................................................... 154
TABLE 6.5 – FLEXIBILITY MATRIX OF DBF FROM TESTS 31, 32 AND 33 (SEE TABLE 6.2)............................ 155
TABLE 6.6 – STIFFNESS MATRIX OF DBF FROM TESTS 31, 32 AND 33 (SEE TABLE 6.2) ............................... 155
TABLE 6.7 – OFF-DIAGONAL AVERAGED STIFFNESS MATRIX OF DBF FROM TESTS 31, 32 AND 33 (SEE TABLE
6.2) ..................................................................................................................................................... 155
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Figures
FIGURE 2.1 ELASTOMERIC DAMPER COMPONENTS (MAHVASHMOHAMMADI, 2013) ..................................... 11
FIGURE 2.2 ELASTOMERIC DAMPER PLACEMENT IN DBF (MAHVASHMOHAMMADI, 2013) ........................... 11
FIGURE 2.3 VISCOUS DAMPER MANUFACTURED BY TAYLOR DEVICES (DONG 2013) ................................... 12
FIGURE 2.4 VISCOUS DAMPER PLACEMENT IN DBF (DONG, 2013)................................................................ 12
FIGURE 2.5 SCHEMATIC OF THE 1ST GENERATION LARGE-SCALE MR DAMPER MANUFACTURED BY LORD
CORPORATION (YANG 2001) ................................................................................................................ 13
FIGURE 2.6 MR DAMPER PLACEMENT IN DBF (DONG, 2013)........................................................................ 13
FIGURE 2.7 SIMPLIFIED DESIGN PROCEDURE AND ELASTIC-STATIC ANALYSIS PROCEDURE (LEE ET AL 2009)
............................................................................................................................................................. 14
FIGURE 2.8 PLAN VIEW OF PROTOTYPE STRUCTURE WITH TRIBUTARY SEISMIC AREA MARKED (DONG,
2013) .................................................................................................................................................... 15
FIGURE 2.9 ELEVATION OF FULL SCALE PROTOTYPE FOR DEVELOPING TEST STRUCTURE (DONG, 2013) ..... 16
FIGURE 2.10 MRF DESIGN FLOW CHART (DONG, 2013)................................................................................ 16
FIGURE 2.11 DBF DESIGN FLOW CHART (DONG, 2013) ................................................................................ 17
FIGURE 3.1 ELEVATION OF 0.6-SCALE TEST STRUCTURE (DONG, 2013) ........................................................ 30
FIGURE 3.2 – ELEVATION OF MRF TEST FRAME ............................................................................................ 31
FIGURE 3.3- MODIFIED WELD ACCESS HOLE DETAILS (AISC 2005) ............................................................. 32
FIGURE 3.4 - 1ST FLOOR WELD ACCESS HOLE DETAILS ................................................................................ 33
FIGURE 3.5 - 2ND FLOOR WELD ACCESS HOLE DETAILS ............................................................................... 33
FIGURE 3.6- 3RD FLOOR WELD ACCESS HOLE DETAILS ................................................................................ 34
FIGURE 3.7 - CONTINUITY PLATE DETAILS ................................................................................................... 34
FIGURE 3.8 – MRF 1ST FLOOR BEAM-TO-COLUMN CONNECTION DETAILS ................................................... 35
FIGURE 3.9 – MRF 2ND FLOOR BEAM-TO-COLUMN CONNECTION DETAILS .................................................. 36
FIGURE 3.10- MRF 3RD FLOOR BEAM-TO-COLUMN CONNECTION DETAILS ................................................. 37
FIGURE 3.11 - MRF GROUND FLOOR BEAM-TO-COLUMN CONNECTION DETAILS ......................................... 38
FIGURE 3.12 - MRF GROUND FLOOR BEAM-TO-COLUMN CONNECTION .......................................................... 39
FIGURE 3.13 – OVERALL ELEVATION OF DBF ................................................................................................ 40
FIGURE 3.14 – ROOF LEVEL DBF BEAM-TO-COLUMN AND T-SECTION CONNECTION DETAILS .................... 41
FIGURE 4.1 – ELEVATION OF BRACING FRAME WITH DBF AND MRF INSTALLED ........................................... 56
FIGURE 4.2 – SECTION A-A OF FIGURE 4.1 .................................................................................................... 57
FIGURE 4.3 – SECTION B-B OF FIGURE 4.1 (NOTE DBF BRACES NOT SHOWN) ............................................. 58
FIGURE 4.4 – PLAN VIEW OF DBF TEST SETUP .............................................................................................. 59
FIGURE 4.5 – PLAN VIEW OF MRF TEST SETUP ............................................................................................. 60
FIGURE 4.6- DBF ASSEMBLY ......................................................................................................................... 61
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FIGURE 4.7- DBF IN BRACING FRAME ............................................................................................................ 62
FIGURE 4.8 – TOP VIEW OF 2ND FLOOR BEAM RBS CUT .................................................................................. 63
FIGURE 4.9 – SIDE VIEW OF 2ND FLOOR BEAM END DETAILS ......................................................................... 64
FIGURE 4.10 – MRF 2ND FLOOR COLUMN WITH DOUBLER AND CONTINUITY PLATES ATTACHED ................. 65
FIGURE 4.11 – MRF BEING ASSEMBLED ........................................................................................................ 66
FIGURE 4.12 – MRF LAID OUT ON LAB FLOOR .............................................................................................. 67
FIGURE 4.13 – MRF ORIENTATION FOR WEB WELD ...................................................................................... 68
FIGURE 4.14- 3RD FLOOR WEB BEFORE WELDING ........................................................................................... 69
FIGURE 4.15- 3RD FLOOR WEB AFTER WELDING .............................................................................................. 69
FIGURE 4.16- MRF ORIENTATION FOR BEAM FLANGE WELDS ...................................................................... 70
FIGURE 4.17- 2ND FLOOR BEAM BOTTOM FLANGE WITH RUN OFF TABS IN PLACE PRIOR TO WELDING ........ 71
FIGURE 4.18- GROUND FLOOR BEAM BOTTOM FLANGE WITH RUNOFF TABS IN PLACE PRIOR TO WELDING 71
FIGURE 4.19- GROUND FLOOR BOTTOM FLANGE WITH RUN OFF TABS, POST WELDING............................... 72
FIGURE 4.20- GROUND FLOOR TOP FLANGE WITH RUN OFF TABS, POST WELDING ...................................... 73
FIGURE 4.21- GROUND FLOOR TOP FLANGE WITH RUN OFF TABS REMOVED AND WELD GROUND .............. 74
FIGURE 4.22 – ACTUATOR DIMENSIONS (SERVOTEST, 2003) ......................................................................... 75
FIGURE 4.23 – TOP VIEW OF LOADING BEAM CONFIGURATION FOR DBF TESTING ....................................... 76
FIGURE 4.24 – SECTION A-A OF FIGURE 4.23 (GONNER 2009) ...................................................................... 76
FIGURE 4.25 – SECTION B-B OF FIGURE 4.23 (GONNER 2009) ....................................................................... 77
FIGURE 4.26 – SECTION C-C OF FIGURE 4.23 (GONNER 2009) ....................................................................... 77
FIGURE 4.27- DBF COLUMN BRACING AND LOADING BEAM SHELVES (DONG 2013).................................... 78
FIGURE 4.28 – N-S ELEVATION OF DBF LOAD ATTACHMENT........................................................................ 79
FIGURE 4.29 – PLAN VIEW OF DBF LOAD ATTACHMENT .............................................................................. 79
FIGURE 4.30- LOADING BEAM SPLICE ............................................................................................................ 79
FIGURE 4.31 – TOP VIEW OF LOADING BEAM CONFIGURATION FOR MRF TESTING ...................................... 80
FIGURE 4.32 – MRF LOADING BEAM SHELF .................................................................................................. 81
FIGURE 4.33 – ELEVATION OF BRACING FRAME (HERRERA 2005) ................................................................. 82
FIGURE 4.34- BRACING FRAME COLUMN REPAIR (DETAIL 1 OF FIGURE 4.33) EAST ELEVATION .................. 83
FIGURE 4.35- BRACING FRAME REPAIR (DETAIL 1 OF FIGURE 4.33) SOUTH ELEVATION ............................... 83
FIGURE 4.36- BRACING FRAME REPAIR (CROSS SECTION A-A OF FIGURE 4.34, BRACING FRAME BEAMS NOT
SHOWN FOR CLARITY) ......................................................................................................................... 84
FIGURE 4.37- PHOTOGRAPH OF BRACING FRAME REPAIR ............................................................................... 85
FIGURE 4.38- BRACING OF LOADING BEAM BY BRACING FRAME (GONNER 2009) ........................................ 86
FIGURE 4.39 – LOCATIONS OF DBF LATERAL BRACING AND LOADING BEAM SHELVES .................................. 87
FIGURE 4.40 – TYPICAL DBF LATERAL BRACING ........................................................................................... 88
FIGURE 4.41- MRF OUT-OF-PLANE BRACING AND LOADING BEAM SHELVES............................................... 89
FIGURE 4.42- MRF 1ST FLOOR BEAM LATERAL BRACING DETAIL ................................................................. 90
ix
FIGURE 4.43- GROUND LINK .......................................................................................................................... 91
FIGURE 4.44- TYPICAL GROUND LINK REACTION SPREADER BEAM AND BRACES (HERRERA 2005) ............. 92
FIGURE 4.45- BAY LINK DETAIL .................................................................................................................... 93
FIGURE 4.46 RIGID LINKS (DONG, 2013)....................................................................................................... 94
FIGURE 4.47- DBF ASSEMBLY ....................................................................................................................... 94
FIGURE 5.1 – DBF FULL BRIDGE LOCATIONS .............................................................................................. 112
FIGURE 5.2 – AXIAL FORCE FULL BRIDGE GEOMETRY AND WIRING SCHEMATIC ........................................ 113
FIGURE 5.3 – BENDING MOMENT FULL BRIDGE GEOMETRY AND WIRING SCHEMATIC ............................... 114
FIGURE 5.4 – MRF COLUMN FULL BRIDGE LOCATIONS .............................................................................. 115
FIGURE 5.5 – BAY LINK INSTRUMENTATION ................................................................................................ 116
FIGURE 5.6 – MRF AND DBF COLUMN AXIAL FORCE AND MOMENT SIGN CONVENTION ........................... 117
FIGURE 5.7 – DBF SOUTH BRACE AXIAL FORCE AND MOMENT SIGN CONVENTION ................................... 117
FIGURE 5.8 – DBF NORTH BRACE AXIAL FORCE AND MOMENT SIGN CONVENTION ................................... 117
FIGURE 5.9 – DBF LOAD CELL LOCATIONS ................................................................................................. 118
FIGURE 5.10 – GROUND LINK LOAD CELL ................................................................................................... 119
FIGURE 5.11 – LOCATION OF DBF DISPLACEMENT TRANSDUCERS.............................................................. 120
FIGURE 5.12 – GROUND LINK DISPLACEMENT TRANSDUCER PLAN ............................................................. 121
FIGURE 5.13 – RIGID LINK DISPLACEMENT TRANSDUCER ........................................................................... 121
FIGURE 5.14 – DBF FLOOR DISPLACEMENT TRANSDUCER .......................................................................... 122
FIGURE 5.15 – DBF T-CONNECTION LVDT PLACEMENT ............................................................................ 123
FIGURE 5.16 – MRF DISPLACEMENT TRANSDUCER LOCATIONS .................................................................. 124
FIGURE 5.17 – RBS LVDT PLACEMENT ...................................................................................................... 125
FIGURE 5.18 – DBF STRAIN GAUGE LOCATIONS ......................................................................................... 126
FIGURE 5.19 – MRF STRAIN GAUGE LOCATIONS ......................................................................................... 127
FIGURE 5.20 – MRF 1ST FLOOR STRAIN GAUGE LOCATIONS ........................................................................ 128
FIGURE 5.21 – MRF 2ND FLOOR STRAIN GAUGE LOCATIONS ....................................................................... 129
FIGURE 5.22 – MRF 3RD FLOOR STRAIN GAUGE LOCATIONS ....................................................................... 129
FIGURE 5.23 – DBF ACCELEROMETER LOCATIONS...................................................................................... 130
FIGURE 5.24 – FREE BODY DIAGRAM USED TO SOLVE COLUMN AND BRACE MOMENTS (FORCES SHOWN
ACTING POSITIVE SENSE) ................................................................................................................... 131
FIGURE 5.25 – TYPICAL FREE BODY DIAGRAM USED TO CALCULATE DBF BEAM FORCES, AND DIAGONAL
BRACE AND COLUMN SHEAR FORCES (FORCES SHOWN ACTING POSITIVE SENSE) ............................ 132
FIGURE 5.26 – TYPICAL FREE BODY DIAGRAM USED TO CALCULATE MRF BEAM FORCES AND COLUMN
SHEAR FORCES (FORCES SHOWN ACTING POSITIVE SENSE) ............................................................... 133
FIGURE 5.27 – DBF EXTERNAL LATERAL FORCE DIAGRAM ........................................................................ 134
FIGURE 5.28 - 3RD STORY DBF FREEBODY DIAGRAM ................................................................................. 135
FIGURE 5.29 – 2ND STORY DBF FREEBODY DIAGRAM ................................................................................ 135
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FIGURE 5.30 – 1ST STORY DBF FREEBODY DIAGRAM ................................................................................. 136
FIGURE 5.31 – MRF EXTERNAL LATERAL FORCES ...................................................................................... 137
FIGURE 5.32 - FREE BODY DIAGRAM USED TO DETERMINE 3RD STORY MRF FRICTION ............................. 138
FIGURE 5.33 – FREE BODY DIAGRAM USED TO DETERMINE 2ND STORY MRF FRICTION ............................ 138
FIGURE 5.34 – FREE BODY DIAGRAM USED TO DETERMINE 1ST STORY MRF FRICTION ............................. 139
FIGURE 5.35 - BAY LINK CALIBRATION FORCE VS VOLTAGE OUTPUT......................................................... 140
FIGURE 6.1 - DBF 1HZ SINUSOIDAL TEST DISPLACEMENTS ........................................................................ 156
FIGURE 6.2 - EXAMPLE 1ST STORY FRICTION FORCE ANALYSIS SINUSOIDAL TEST #11 .............................. 157
FIGURE 6.3 - EXAMPLE 2ND STORY FRICTION FORCE ANALYSIS SINUSOIDAL TEST #11 ............................. 157
FIGURE 6.4 - EXAMPLE 3RD STORY FRICTION FORCE ANALYSIS SINUSOIDAL TEST #11 ............................. 158
FIGURE 6.5 - DBF STIFFNESS MATRIX DEGREES OF FREEDOM .................................................................... 159
FIGURE 6.6 - TYPICAL FORCE-DISPLACEMENT GRAPH USED IN DETERMINING FLEXIBILITY COEFFICIENTS160
FIGURE 6.7 - T-CONNECTION MODIFICATIONS ............................................................................................. 161
FIGURE 6.8 - STATIC TEST RESULTS LOADING AT 3RD FLOOR BEFORE AND AFTER T- CONNECTION
MODIFICATION ................................................................................................................................... 162
FIGURE 6.9 – 1ST FLOOR T-CONNECTION MOMENT ROTATION BEHAVIOR ................................................... 163
FIGURE 6.10 – 2ND FLOOR T-CONNECTION MOMENT ROTATION BEHAVIOR ............................................... 163
FIGURE 6.11 – 3RD FLOOR T-CONNECTION MOMENT ROTATION BEHAVIOR ............................................... 164
FIGURE 6.12 – 1ST FLOOR T-CONNECTION AXIAL FORCE VS DEFORMATION .............................................. 164
FIGURE 6.13 – 2ND FLOOR T-CONNECTION AXIAL FORCE VS DEFORMATION ............................................... 165
FIGURE 6.14 – 3RD FLOOR T-CONNECTION AXIAL FORCE VS DEFORMATION ............................................... 165
FIGURE 6.15 - STATIC TEST RESULTS LOADING AT 3RD FLOOR BEFORE AND AFTER TIGHTENING RIGID LINKS
........................................................................................................................................................... 166
FIGURE 6.16 - 1ST STORY RIGID LINK AXIAL FORCE-DEFORMATION BEHAVIOR .......................................... 167
FIGURE 6.17 - 2ND STORY RIGID LINK AXIAL FORCE-DEFORMATION BEHAVIOR ......................................... 167
FIGURE 6.18 - 3RD STORY RIGID LINK AXIAL FORCE-DEFORMATION BEHAVIOR ......................................... 168
FIGURE 6.19 - SOUTH GROUND LINK AXIAL FORCE-DEFORMATION BEHAVIOR .......................................... 168
FIGURE 6.20 - NORTH GROUND LINK AXIAL FORCE-DEFORMATION BEHAVIOR ......................................... 169
FIGURE 6.21– BAY LINK CALIBRATION FORCE-HEAD TRAVEL RESPONSE .................................................. 170
FIGURE 6.22 - COMPARISON OF 1ST STORY DISPLACEMENTS FOR NS COMPONENT OF THE EL CENTRO
GROUND MOTION ............................................................................................................................... 171
FIGURE 6.23 - COMPARISON OF 2ND STORY DISPLACEMENTS FOR NS COMPONENT OF THE EL CENTRO
GROUND MOTION ............................................................................................................................... 171
FIGURE 6.24 - COMPARISON OF 3RD STORY DISPLACEMENTS FOR NS COMPONENT OF THE EL CENTRO
GROUND MOTION ............................................................................................................................... 172
xi
Abstract
Large scale structures with dampers are being studied as part of ongoing research related
to the use of dampers to limit seismically induced damage. Large scale frame testing is
being conducted at Lehigh University in collaboration with Purdue University, the
University of Illinois, City College of New York, the University of Connecticut, and the
Lord Corporation under an NSF-funded NEESR research project. A test bed consisting
of a 0.6-scale moment resisting frame (MRF) and a 0.6-scale damped brace frame (DBF)
will be used in testing different types of dampers.
A simplified design procedure is used to design the test frame. This procedure uses
strength considerations to design a lateral load resisting frame, then allows an engineer to
add damping devices to ensure the frame does not exceed other performance objectives,
in this case drift limits. The fabrication and erection of this test frame were conducted at
the NSF NEES RTMD Earthquake Simulation Facility at the ATLSS Center at Lehigh
University in Bethlehem, PA.
This thesis focuses on the experimental setup of the two 0.6-scale test frames. The DBF
test frame was characterized to determine its as-built structural characteristics and to
ensure the experimental setup functioned properly. A static stiffness matrix was
developed to compare with computer models of the structure, for use in hybrid testing
and in developing semi-active control laws. This was achieved using static testing and a
flexibility approach. Full-bridge load cells installed on the members of the DBF were
used to obtain the internal member forces for the beams, columns, and diagonal braces.
An assessment of the results indicated the distribution of member forces in the DBF is as
1
expected and that the level of friction in the test setup (between the DBF and bracing
frame) is low and well within the acceptable range.
2
Chapter 1.
Introduction
1.1 Overview
Dampers have been used for many years to improve the seismic response of buildings.
They accomplish this task by adding supplemental damping to a structural system to
reduce the drift and inelastic deformation demands of the primary lateral load resisting
system and by reducing the acceleration and velocity demands of non-structural
components. Current research is trying to improve the design process by integrating the
design of the supplemental damping system with the design of the structural system to
produce an efficient and effective design. To accomplish this goal, a simplified design
procedure for buildings with passive damping devices has been developed that is
practical, probabilistic and performance-based. The procedure is based on designing the
system for the code design base shear (i.e., strength) and using dampers to meet
performance objectives for the design (e.g., drift control; or members remaining elastic.)
With the goal of producing a simplified design procedure, several steps need to be
completed. They include validating the simplified design procedure using large-scale
real-time hybrid testing. To accomplish this task a prototype steel structure with a
supplemental damping system was designed using the simplified design procedure. A
0.6-scale test structure consisting of a damped braced frame (DBF) to house the dampers
and a moment resisting frame (MRF) to provide strength is designed and constructed.
3
This research is being conducted within the National Science Foundation (NSF) George
E. Brown, Jr. Network for Earthquake Engineering Simulation Research (NEESR)
program. It is a joint project between researchers at Lehigh University, Purdue
University, the University of Illinois, City College of New York, the University of
Connecticut, and the Lord Corporation. Experiments of the test structure described herein
take place at the Real-Time Multi-Directional (RTMD) Earthquake Simulation Facility at
the Advanced Technology for Large Structural Systems (ATLSS) Center at Lehigh
University.
1.2 Objective
The objective of this thesis is to document the details and characterization tests of a 0.6scale 3-story steel test structure. This thesis describes detailed planning and construction
of the test structure, the experimental setup, and measuring of the test structure static
characteristics. It serves as a reference for the test program in which the test structure will
be tested.
1.3 Scope of thesis
The work covered in this thesis is a follows. Chapter 2 presents background information
of the use of dampers in building structural systems, the simplified design procedure, and
the prototype structure. Chapter 3 discusses the layout and design of the 0.6-scale test
structure, including the design details. Chapter 4 discusses the fabrication and
experimental setup for the test structure. Also covered are the design of the loading
system, reaction points, lateral bracing and other components of the test setup. Chapter 5
covers the instrumentation needed to measure deformations, reactions and internal
4
member forces in the test structure. Also covered is the assessment of other members
forces and test frame reactions using measured responses and statics. Chapter 6 discusses
the characterization of the DBF using static and sinusoidal testing. It includes the
assessment of frictional forces in the test setup and the development of the frame’s static
stiffness matrix.
Chapter 7 provides a summary and conclusions of the thesis and
recommendations for future work.
5
Chapter 2.
Background
2.1 General
This chapter serves to provide background on the overall research project. It begins by
discussing various types of supplemental damping devices for seismic hazard mitigation.
It then discusses a simplified design procedure for designing structures with supplemental
damping systems and concludes by describing the prototype structure that will be used
for the NEESR studies at Lehigh.
2.2 Supplemental damping systems
Supplemental damping systems can be used to reduce the response of a structure
subjected to seismic forces, and thus enhance the structure’s performance. Supplemental
damping systems accomplish this by supplementing the inherent damping in the
structure. Damping devices can be passive, active, or semi-active devices. Their
classification is based on how the damping properties of the device are controlled.
Passive damping devices are one in which the damper does not have the ability to change
its properties. Passive dampers are widely used in the structural engineering community
due to their simplicity and relative stability. Passive damping devices dissipate energy
using a variety of methods including component yielding, friction, phase transformation
in metals or deformation of visco-elastic solids or fluids (Soong and Spencer 2002).
6
In semi-active and active controlled damping devices their responses are monitored by a
computer. The computer has a control law that modifies the characteristics of the damper
to allow it to provide the appropriate level of damping that would better control the
response of the structural system.
The test program discussed in this thesis considered two types of passive dampers
(elastomeric dampers and viscous fluid dampers) and one type of semi-active damping
device (magneto-rheological (MR) dampers). The elastomeric dampers use an
elastomeric material compressed inside a steel tube section that provides damping
through shear deformation of the elastomer and friction. One of the goals of a portion of
the overall research project is to develop a new generation of these low cost dampers
(Mahvashmohammadi, 2013). Figure 2.1 and Figure 2.2 show a single damper and the
placement of a group of dampers in the test structure, respectively.
Viscous fluid dampers use a viscous fluid to produce a damping force. The viscous
dampers used in this study were manufactured by Taylor Devices and can develop a
maximum nominal damper force of 130 kips. Figure 2.3 is a schematic of a similar
viscous damper manufactured by the Taylor Devices that is similar to the one used in this
study and Figure 2.4 shows the placement of the viscous dampers in the test structure.
MR dampers have iron-carbon particles suspended in a fluid, where the particles are
aligned using a magnetic field. Aligning the particles changes the viscosity of the fluid.
This fluid passes through orifices near the circumference of the damper piston head,
where a change in viscosity increases the damper force. The MR dampers used in this
study are manufactured by the Lord Corporation and have a maximum nominal damper
7
force of 70 kips. Figure 2.5 is a schematic of an MR damper that is similar to the one
used in this study. Figure 2.6 shows the placement of the MR dampers in the test
structure.
2.3 Simplified design procedure
A simplified design procedure (SDP) for designing with supplemental passive damping
devices has been developed by Lee et al. (2005). It differs from typical methods of
designing structural systems with dampers, where instead of using numerical
optimization algorithms to locate and size supplemental dampers for an existing structure
the SDP uses practical analysis and a design procedure to integrate the design of the
supplemental dampers into the structural design. The procedure involves designing the
structural system for the code design strength and then uses dampers to meet performance
objectives for the design (e.g., drift control or members remaining elastic.)
In the SDP a trial MRF of lateral stiffness Ko is selected. Then a range of values for the
design parameters α (which represents the ratio of diagonal bracing lateral stiffness to
MRF lateral story stiffness) and β (which represents the ratio of damper stiffness to MRF
lateral story stiffness)is selected for the selected values of α and β a first-modal period for
the structure and damping reduction factor, B, are determined, enabling the seismic
coefficient for the design base shear to be established. An equivalent lateral force
analysis is then performed. The design having the smallest α and β values that satisfies
the design performance objectives is chosen. Based on the value for β, the dampers are
then designed. This process can then be iterated to improve the MRF design. Figure 2.7
shows a flow chart of the SDP developed by Lee et al. using visco-elastic (VE) dampers.
8
2.4 Prototype structure
In order to evaluate the SDP a prototype structure was designed by Dong (2013) using
the procedure. The prototype structure is assumed to be located in Southern California,
with a Seismic Group of I, a Site Class of D, and a Seismic Category of D. It was
designed using the 2006 IBC Code. The structure is three stories tall with a basement. It
has a symmetrical floor plan consisting of 6 bays by 6 bays, with each being 25ft in
width. Figure 2.8 shows the floor plan of the prototype structure, where moment resisting
frames (MRF) and the damped braced frames (DBFs) are labeled. Because of the
symmetrical layout of the building only one quarter of the building will be considered in
the creation of the test structure. The seismic tributary area of the floor plan for the test
structure is indicated in Figure 2.8. In the experimental study ground motions in only one
direction are considered (e.g, North-South), therefore only one MRF and one DBF are
considered for the test structure.
Assuming a rigid floor diaphragm (i.e. a composite slab) the DBF and MRF in the northsouth direction are assumed to have the same drift in the test structure, are therefore
aligned side by side in the test structure. Figure 2.9 shows an elevation of the test
structure. The lean-on column represents the gravity load system within the tributary
area. The seismic weight and mass of ¼ of the building floor plan is applied on a lean-on
column at each floor level.
In developing performance objectives the seismic hazard levels defined by FEMA (2003)
for the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE)
are used. The MCE is defined as an earthquake having a 2% probably of occurrence in 50
9
years. The DBE is an earthquake with 2/3rds the intensity of the MCE with
approximately a 10% probability of occurrence in 50 years. The performance objectives
for the design of the prototype structure are as follows: (1) 1.5% maximum drift under
DBE; (2) the DBF remains elastic under the DBE; and (3) 2.5% maximum drift under
MCE. These performance objectives were incorporated into the design of the MRF and
DBF using the SDP, see Figure 2.10 and Figure 2.11.
Further details of the specific design of the prototype structure appear in Dong (2013).
10
Figure 2.1 Elastomeric Damper Components (Mahvashmohammadi, 2013)
Figure 2.2 Elastomeric Damper Placement in DBF (Mahvashmohammadi, 2013)
11
Figure 2.3 Viscous Damper Manufactured by Taylor Devices (Dong 2013)
Figure 2.4 Viscous Damper Placement in DBF (Dong, 2013)
12
Figure 2.5 Schematic of the 1st Generation Large-Scale MR Damper Manufactured by
Lord Corporation (Yang 2001)
Figure 2.6 MR Damper Placement in DBF (Dong, 2013)
13
Figure 2.7 Simplified Design Procedure and Elastic-Static Analysis Procedure (Lee et al
2009)
14
Figure 2.8 Plan View of Prototype Structure with Tributary Seismic Area Marked (Dong,
2013)
15
Figure 2.9 Elevation of Full Scale Prototype for Developing Test Structure (Dong, 2013)
Figure 2.10 MRF Design Flow Chart (Dong, 2013)
16
Figure 2.11 DBF Design Flow Chart (Dong, 2013)
17
Chapter 3.
Design of Test Structure
3.1 General
A scale model of the prototype structure had to be developed in order to allow for testing
in the ATLSS laboratory. Based on space restrictions, a 0.6-scale model was chosen. To
design this scaled model the bay widths and floor heights where scaled to 0.6 their
original sizes. In order to allow the SDP to be used the lateral applied forces were scaled.
(Dong, 2013) These scaled forces were then used to determine member sizes via the SDP.
Figure 3.1 shows the scaled configuration of the frame, which will tested in the lab.
Using the SDP the MRF was designed first using 100 percent of the scaled design base
shear. A summary of scaled lateral forces as well as distributed gravity loads used by
Dong for the design of the MRF test structure are listed in Table 3.1 The MRFs beams
and columns were designed for strength, where drift limits and other performance
objectives are not considered at this point. In order to protect the beam-to-column welds
the MRF was designed with reduced beam section (RBS) connections. These will be
described in detail later.
After the MRF was designed, the damped braced frame (DBF) was designed based on the
performance objectives that: 1) the system remain elastic under the DBE; and 2) the
system develop no more than 1.5% story drift during the MCE. Because several different
damper types are going to be used during the test program, the maximum expected
18
damper force for each type of damper had to be considered. The force from the
elastomeric dampers controlled the design.
All structural steel sections used for the two frames is A992 Grade 50 steel. All plates
used in the construction are A572 Grade 50 steel.
3.2 MRF design and layout
The moment frame of the test structure that was constructed for laboratory testing was a
one bay three story MRF with RBS connections. The beams and columns used in both the
prototype MRF and the scaled test specimen MRF are listed in Table 3.1. This scaled
MRF will be used for numerous earthquake tests before it needs to be replaced. After the
beams are damaged to the degree where they need to be replaced, they will be removed
and replaced, but the columns will be reused for the next series of tests. With this in mind
RBS connections were chosen. They will act as fuses and help protect the column from
sustaining significant damage during a test, because they will yield before the column
yields. These fuses will ensure that the connection satisfies a weak beam-strong column
configuration. Additionally they will help protect the beam-to-column connection from
damage which could result in low cycle fatigue. The selected RBS dimensions are shown
in Table 3.3. Figure 3.2 shows an elevation of the layout of the MRF that was chosen.
3.2.1
Beam-to-column connections
The moment frame used for laboratory testing had two major objectives. The first
objective was to function as much as possible as a traditional MRF and second was to be
relatively easy to replace after sustaining damage. It was with these two goals in mind
two different beam-to-column connection designs were considered. The first was a bolted
19
end plate connection. The second was a standard moment connection with fully welded
flanges and a welded web.
The bolted end plate connection was considered because it could be easily replaced after
the beam sustained damage during testing. It featured a beam with reduced beam sections
cut into it and an endplate attached to either end of the beam with full penetration welds.
These welds would be to detailed to satisfy the 2005 AISC Seismic Provisions (AISC
2005b). To connect the end plate to the column several bolts would be used. These bolts
were sized to avoid overcoming their pre-compression force when the beam was
subjected to combined axial tension force and moment. Once the beam had sustained
damage the connections would be unbolted and replaced with another beam with end
plates that had been prefabricated.
There were several drawbacks of the bolted end plate configuration. One was that it
would be more costly than a traditional fully welded connection due to the costs
associated with fabricating the end plates and the bolts. Another drawback was the
difficulty in finding a bolt configuration that would satisfy the anticipated level of force
in the beam without overcoming the pre-compression force in the bolts. This is important
because any gap opening in the connection could affect the test results. Due to the width
of the column flanges, only a limited number of bolts could be used in the connection.
This number of bolts did not allow for a connection that would satisfy the requirement to
not overcome the pre-compression force with either A325 of A490 bolts. The final
drawback of this proposed connection type was that the bolted end plate is not a
prequalified connection for seismic applications, as defined under the 2005 AISC Seismic
Provisions (AISC 2005b).
20
Due to the limitations of the endplate design it was therefore decided that a traditional
fully welded connection would be used. In designing this connection it was important to
consider the purpose of the connection. Steel MRFs were developed in the 1960s and are
designed to be ductile during seismic shaking. The design of these connections typically
featured full penetration welds used to connect the beam flanges to the column and a
shear tab that bolted to the beam web. However during the Northridge Earthquake of
January 17, 1994 many buildings featuring this design suffered brittle fractures of their
beam-to-column connections. In an effort to avoid this problem in future earthquakes,
several studies of traditional moment frames were conducted. These included the SAC
(2000) studies that subjected numerous moment connections to cyclic loading. It was
determined that four primary factors led to the failures: 1) weld toughness; 2) weld access
hole geometry; 3) inadequate panel zone strength; and 4) inadequately restrained beam
webs. These factors were incorporated into the FEMA 350 (FEMA 2000)
recommendations and later adopted in AISC 341-05 Seismic Provisions for Structural
Steel Buildings (AISC 2005b) and AISC 358-05 Prequalified Connections for Special
and Intermediate Steel Moment Frames for Seismic Applications (AISC 2006). All three
of these documents were used to detail the connections for the MRF.
3.3 MRF details
The following describes the details of the MRF test structure and why they were chosen.
3.3.1
Weld Access Holes
Special consideration was given to the weld access hole geometry because studies have
indicated that weld access hole geometry has a significant effect on the ductility of MRFs
21
(Ricles et al. 2004). These studies resulted in a specification for a modified weld access
hole, which is included in the AISC seismic specification (AISC 2005b). Figure 3.3
shows a schematic of the modified access hole that appears in the specification. The exact
weld access hole geometry used for the MRF beam-to-column connections is provided in
Figure 3.4 through Figure 3.6.
3.3.2
Panel Zone Design
Special care was taken to not only follow but to exceed recommendations for panel zone
strength in the MRF, because the frame will be used for numerous tests. Reinforcement
consisted of continuity plates at all floor levels and doubler plates at the 1st, 2nd and
ground floors.
3.3.2.1 Continuity Plates
Under the AISC 358-05 (AISC 2006) continuity plates are required for all SMRFs not
meeting a very limited set of exceptions, which this frame did not meet. The provision
allows for a one-sided connection like the one designed for this moment frame to have a
continuity plate with a thickness that is at least one-half the thickness of the beam flange,
but requires a two sided connection to have a continuity plate at least the full thickness of
the beam flange. In an effort to minimize panel zone damage as much as possible in order
to reuse the columns in future testing, a plate roughly as thick as the beam flange was
chosen for each floor. Table 3.4 summarizes the plate size chosen as well as the beam
flange size. All plates were A572 Grade 50 steel.
The design of each continuity plate was the same regardless of floor, because besides
thickness the geometry depended on the column. Care was taken to fit the plates in such a
22
manner as to avoid welding in the columns k-region. Figure 3.7 shows the layout of the
continuity plates. Each continuity plate was attached to the column web with a two sided
¼ inch fillet weld and to the column flange by a groove weld. Both welds used an E70T1electrode. Details showing the placement of the continuity plates and welds can be
found in Figure 3.8 through Figure 3.10.
The original design of the ground floor continuity plates would interfere with the bolts
that attached the ground link to the frame, and therefore the continuity plate design had to
be modified to accommodate the bolts. The easiest solution was move the continuity
plates below the beam flange and add a second set and equal distance above the beam
flange. The same thickness of plate was used for simplicity.
A drawing of this
configuration is shown in Figure 3.11; Figure 3.12 shows the final configuration with the
ground link attached.
3.3.3
Doubler Plates
AISC 341-05 (AISC 2005b) requires panel zones to be able to resist the shear force
created by the maximum expected beam moment developed at the column face. To check
that this minimum thickness was sufficient, the shear demand associated with the
maximum expected beam moment at the face of the column was compared to the panel
zone shear capacity. The shear capacity was calculated using the following equation,
which is based on the AISC Seismic Provision (AISC 2005b) and includes only the
contribution of the column web and doubler plates to the panel zone shear capacity:
𝑉𝑝𝑧 = 0.55 ∗ 𝐹𝑦 𝑑𝑧 (𝑡𝑐𝑤 + 2𝑡𝑑𝑜𝑢𝑏𝑙𝑒𝑟 )
where:
23
(3-1)
𝑉𝑝𝑧 = shear resistance of panel zone, kips.
𝐹𝑦 = the yield stress of the panel zone components, ksi
𝑑𝑧 = panel zone depth between continuity plates, inch
𝑡𝑐𝑤 = thickness of column web, inch
𝑡𝑑𝑜𝑢𝑏𝑙𝑒𝑟 = thickness of each doubler plate, inch
Only the third floor beam was able to achieve this requirement without additional
strengthening. A pair of doubler plates was sized for the 1st, 2nd and ground floors that
would allow this requirement to be met. In order to minimize shear buckling in the panel
zone doubler plates during inelastic deformations the AISC Seismic Provisions (ASIC
2005b) require the panel zone to meet the following minimum thickness requirement:
t ≥ (𝑑𝑧 + 𝑤𝑧 )⁄90
(3-2)
where:
t = thickness of column web or doubler plates or column web and doubler plates if plug
welds are used, inch
𝑤𝑧 = panel zone width between column flanges, inch
Again the 3rd floor panel zone met this criterion. The doubler plates installed at the other
floors however required plug welds in order to meet this requirement. In addition to the
plug welds a half inch slot weld was used to attach the doubler plate to the column flange.
Special consideration was taken to limit the size of the weld in the column k region. At
24
the top and bottom of the doubler plate a fillet weld was used. All welds were made using
an E70T-1 electrode. Doubler plates were sized to continue about 5 inches above and
below the beam. The final doubler plate sizes, along with column web thicknesses are
summarized in Table 3.5 and drawings of beam-to-column connection details at each
floor are show in Figure 3.8 through Figure 3.10.
3.3.4
Weld criteria
Weld criteria for the MRF welds was adapted from that used by Zhang (2005). All welds
were specified to conform to the AWS 5.20-95 Specification and Section 4.2 of AWS
D1.1/D1.1M:2005 (AWS 2005), and were performed using the flux core arc welding
procedure. An E70T-1 electrode was used for all “shop” welds, and an E7018 electrode
was used for the flange and web full penetration welds. All welds used to fabricate the
frames had a minimum Charpy V-Notch toughness of 20 ft-lbf at -20°F and 40 ft-lbf at
70°F by AWS classification test methods. Further details about the welding of these
connections are presented in Chapter 4.
3.4 DBF design and layout
The Damper Braced Frame (DBF) test structure was designed by Dong to be used as a
test bed for testing various dampers (Dong 2013). It was designed to remain elastic
during all testing to allow it to be used numerous times. The DBF is a three story one bay
structure with an inverted chevron bracing configuration. The columns are W8x67
sections, the beams are all W12x40 sections and the braces are HSS8x6x3/8 sections. An
overall layout of the frame is shown in Figure 3.13.
25
The frames beams are not continuous but have a T-section connection located 2ft from
the centerline of the column. The purpose of the connection is to allow for a pinned
connection that would limit the moment developed within the gusset plate region. In
order to avoid slipping in the T-section connection a set of tapered pins were used in
addition to bolts. This connection was designed to transfer only shear and axial force in
the beam and thus act like a pin. Figure 3.14 shows a schematic of this connection.
Further details of this connection including design forces are available in Dong (2013).
Also shown in Figure 3.14 are details of the upper gusset plate and beam-to-column
connection.
The DBF was detailed by Dong and further details can be found in his dissertation (Dong,
2013).
26
Table 3.1 - MRF Test Structure Design Loads
Floor
1st Floor Lateral
2nd Floor Lateral
3rd Floor Lateral
Distributed Dead Load
Distributed Live Load
0.6-scale Test Frame
89 kips
62 kips
44.6 kips
0.17 klf
0.13 klf
Table 3.2 - MRF Member Sizes
Member
Columns
Ground Floor Beam
1st Floor Beam
2nd Floor Beam
3rd Floor Beam
Prototype MRF
W14X176
W30X124
W30X124
W21X122
W16x50
27
0.6-scale Test Structure
W8X67
W18x46
W18x46
W14x38
W10x17
Table 3.3 – 0.6 Scale Test Structure RBS Dimensions
Location
1st Floor Beam
2nd Floor Beam
3rd Floor Beam
a (in)
4.5
4.5
4.5
b (in)
13
12
8.5
c (in)
1.4375
1.375
0.875
Table 3.4 – 0.6 Scale Test Structure Continuity Plate Sizes
Continuity Plate
Thickness (in)
Beam Flange
Thickness (in)
Steel Type
Ground
0.625
0.605
A572 Gr50
1st
0.625
0.605
A572 Gr50
2nd
0.500
0.515
A572 Gr50
3rd
0.313
0.330
A572 Gr50
Floor
28
Table 3.5 - 0.6 Scale Test Structure Doubler Plate Sizes
Floor
Doubler Plate Depth
Above Beam (in)
Plate Thickness (in)
Web
Thickness (in)
Steel
Type
Ground
5
0.375
0.605
A572
Gr50
1st
5
0.375
0.605
A572
Gr50
2nd
5
0.3125
0.515
A572
Gr50
3rd
-
-
0.330
A572
Gr50
Table 3.6 - DBF Member Sizes
Member
Columns
Ground Floor Beam
Beams
Braces
Tees
Prototype DBF
W14X176
W
W
HSS
-
0.6-scale Test Structure
W8X67
W12x40
W12x40
HSS8x6x3/8
WT5x15
Table 3.7 – 0.6 Scale Test Structure DBF Components
Component
Gusset Plate
Thickness (in)
Steel Type
Upper
Gusset
0.375
A572 Gr50
Lower
Gusset
0.5
A572 Gr50
29
Figure 3.1 Elevation of 0.6-Scale Test Structure (Dong, 2013)
30
Figure 3.2 – Elevation of MRF Test Frame
31
Figure 3.3- Modified Weld Access Hole Details (AISC 2005)
32
Figure 3.4 - 1st Floor Weld Access Hole Details
Figure 3.5 - 2nd Floor Weld Access Hole Details
33
Figure 3.6- 3rd Floor Weld Access Hole Details
Figure 3.7 - Continuity Plate Details
34
Figure 3.8 – MRF 1st Floor Beam-to-Column Connection Details
35
Figure 3.9 – MRF 2nd Floor Beam-to-Column Connection Details
36
Figure 3.10- MRF 3rd Floor Beam-to-Column Connection Details
37
Figure 3.11 - MRF Ground Floor Beam-to-Column Connection Details
38
Figure 3.12 - MRF ground floor beam-to-column connection
39
Figure 3.13 – Overall elevation of DBF
40
W8x67
W12x40
Figure 3.14 – Roof Level DBF Beam-to-Column and T-Section Connection Details
41
Chapter 4.
Experimental Setup
4.1 General
This section describes the fabrication and erection of the DBF and MRF of the test
structure. It also describes the experimental test setup for the test structure. The test setup
consists on the components shown in Figure 4.1 through Figure 4.5. These components
include the MRF and DBF, 3 actuators, an external bracing frame to provide out of plane
bracing while allowing in plane movement, a set of loading beams at each floor to apply
lateral forces from the actuators, a pair of ground links and a bay link. Details of the
loading system, out-of-plane bracing of the structure and ground links are provided in this
chapter.
The DBF frame was constructed and installed prior to the MRF frame being constructed.
This allowed the DBF to be tested independently. Modifications made to the original test
setup to allow the MRF to be tested are noted in this chapter.
4.2 Fabrication and erection
Both frames were constructed at the ATLSS Center.
4.2.1
Measured section properties
The member sections and components were measured when they arrived from the mill.
This information was needed for use in instrumentation calibration. The measured and
nominal section properties are listed in Table 4.1 and Table 4.2.
42
4.2.2
DBF fabrication
The DBF was fabricated in the horizontal position as shown in Figure 4.6. It was then
moved to the test setup to be tested. Figure 4.7 shows the DBF in the bracing frame. After
it was placed in the bracing frame the ground links were attached to the columns. The
loading beam support shelves were then attached to the columns. The loading beam
system was then installed and posttensioned to 500 kips. The loading beam to frame
connection was installed at this time. External bracing was then added to brace the
beams.
Due to the initial availability of only one actuator, a single actuator was installed for a
brief period of testing, and then the other two actuators were attached. More details of the
fabrication and erection can be found in Dong (2013).
4.2.3
MRF fabrication
The MRF was fabricated in several phases. The first phase of frame construction
consisted of cutting the beams to the appropriate length. Once this was completed the
beams were laid out and the reduced beam sections cut. This was done with a template to
ensure that each beam was cut to the same precision. Once the section was laid out the
RBS section was cut using a torch. After cutting, the profile was then ground to a surface
roughness of 250 µinch using various grinding tools, finishing with a pencil grinder. The
RBS was inspected to ensure that the proper dimensions had been reached and the proper
maximum roughness had been achieved. Figure 4.8 shows the completed 2nd floor
reduced beam section prior to assembly.
43
The next phase involved prepping the ends of the beams to allow the full penetration
welds to the column to be made. This prep work included beveling both the web and the
flange of each beam, drilling erection bolt holes and fabricating the weld access holes.
The weld access hole profiles specified in Figure 3.4 through Figure 3.6 were used. The
beam webs were beveled to 45º and the flanges were tapered to 30º. Figure 4.9 shows the
completed 2nd floor beam end detail.
The columns also needed to be prepped. The first part of prepping the columns involved
installing doubler plates. While welding the plates to the column flange care was taken to
avoid buildup of weld in the k region of the column as this would lead to cracking. After
doubler plates were installed continuity plates were installed on the beams. Finally, shear
tabs were installed at each floor to attach the beams to the column. These shear tabs
served two purposes. First they aided in the erection and alignment of the frame. And
secondly they served as permanent backing bars for the beam web-to-column full
penetration weld. Doubler plates were also installed at this time. The welds connecting
the doubler plates to the column were all made using an E70-T1 electrode. Figure 4.10
shows the second floor column with all plates welded into place.
For efficiency, the MRF was bolted together using ½ inch erection bolts placed through
the shear tabs in the horizontal plane. Bolting it horizontally assured that the frame was
both square and plumb. Figures Figure 4.11 and Figure 4.12 show the frame being
assembled in this manner. The column base plates were tacked into position at this time.
Also while in this position backing bars and runoff tabs were installed on the flanges to
allow the beam flange full penetration weld to be completed later. Two welds between
the beam web and the shear tab, reinforcing each shear tab was also placed at this time.
44
To weld the beam webs the frame was tipped on its side as shown in Figure 4.13. This
was done to allow easy access to the welds. It was felt that it was not necessary to
replicate the typical field condition (vertical) for these welds because they were less
likely to fail then the beam flange welds. Figures 4.14 and 4.15 show the 3rd floor web
before and after welding.
The frame was then positioned vertically to complete the flange welds. This was done in
an effort to simulate field conditions. These welds carry the most force and are the most
likely to fail so it was important that they were done as close to field conditions as
possible. Figure 4.16 shows the frame in the configuration that the flange welds were
completed. The beam flange welds were made using multiple passes to fill the groove.
While the frame was in this vertical configuration the base plates were welded to the
columns. Figure 4.17 and Figure 4.18 show the ground floor beam top flange and 2nd
floor bottom flange prior to welding and Figure 4.19 and Figure 4.20 show the same
flanges after welding, prior to the removal of the runoff tabs. Figure 4.21 shows a flange
after the removal of the runoff tabs.
After welding was complete the full penetration welds were tested using the ultrasonic
testing method. The welds were certified using the static loading criteria of AWS D.1.12010 Article 6 Part F. One weld failed inspection, and was subsequently repaired and
reinspected. It subsequently passed. A copy of the ultrasonic testing report is available in
the Appendix.
After all welding was completed the backing bars and run off tabs on the lower flange of
all beams were removed and the weld was backgouged to bare metal. A reinforcing weld
45
was then applied. The run off tab from the top flange was removed but the backing bar
was left in place. The welds were then profiled. Figure 4.21 shows a representative weld
profile. The web welds were left as they were and were not profiled.
Shelves to support the loading beams were attached then attached to the columns. Details
of these shelves are discussed in section 4.3.2. After the frame had been completely
welded all strain gauges and full bridges were installed, prior to the test frame being
placed in the bracing frame. Small holes were drilled into the top of the columns in order
to attach rigging to lift the frame. This was done to avoid yielding the 3rd story beam. The
frame was lifted into the bracing frame and attached to the base crevices. With the test
specimen in place the loading beam extensions described in section 4.3.2 were put in
place and the ground link and bay link were installed. Finally lateral bracing was installed
to support the test specimen.
4.3 Loading system
The test structure was loaded at each floor level by one hydraulic actuator. The actuators
have a stroke of ±500 mm (±19.7 inch). The first floor actuator (model 200-100-1700)
has a capacity of 2300 kN (517 kips) while the second and third floor actuators (model
200-100-1250) have a capacity of 1700 kN (382 kips). A summary of the hydraulic
characteristics of the actuators can be found in
Table 4.3. Figure 4.22 shows the dimensions of the actuators.
4.3.1
DBF loading system
46
The actuators were attached to the DBF frame using a set of loading beams. Each set of
loading beams consisted of a pair of HSS 12X12X3/8 beams with two 1.5 inch
Dywidag® rods threaded through each beam. The rods were connected to a mounting
plate on the actuator on the north end and to a steel I-section on the south end. This
configuration is shown in Figure 4.23 through Figure 4.26. The whole system was then
posttensioned to 500kips to ensure that it would not develop any decompression during
testing. The loading beams were supported on shelves, which were also used to laterally
brace the columns as shown in Figure 4.27.
To attach the loading beams to the DBF a load attachment was designed. This attachment
needed to serve two purposes: 1) it had to allow force transfer force from the loading
beams to the DBF without slipping; 2) it had to be detachable in order allow
characterization testing of the MRF of the test structure. To achieve these goals a series
of bolted and welded plates was developed. Designs for this connection can be seen in
Figure 4.29 and Figure 4.28. Note that the lower plate has tapped holes while the upper
plate has smooth holes. This prevents the connection from slipping and still allows it to
be detached for future MRF characterization, thus accomplishing both goals of the
connection. This connection was designed for 200 kips of axial force in each tube.
4.3.2
MRF loading system
Due the fact that characterization testing of the MRF and DBF was to be conducted in
two phases, the initial loading beam configuration had to be modified to allow the MRF
to be loaded. This involved adding an additional 19’-2” to the loading beams. In order for
this to happen the loading beam end piece at the south end of the DBF was removed from
the original loading beam configuration and moved to the south side of the MRF. A 19’47
2” long section of loading beam was added and the Dywidag® rods were lengthened
using couplers. The beams were spliced using the series of welds and lap plates shown in
Figure 4.30. The splice was designed to carry 300 kips in each beam for a total of
600kips, which exceeds the capacity of the actuator. The final configuration for loading
both frames is shown in Figure 4.31.
The four Dywidag® rods were each tensioned to 125 kips to posttension the beam and
actuator attachment assembly together with 500kips of force thus ensuring that during
testing no decompression would occur.
In order to support the beams a pair of shelves was attached to each column. The beams
then rested on these shelves. These shelves were similar to the shelves on the DBF, but it
was important to make the shelves on the MRF detachable so that once the frame
sustained damage it could be lifted up to repair the beams. Figure 4.32 shows the layout
of this system of shelves.
4.4 Bracing of test structure
The test specimen will be tested in the north-south direction and thus needed to be braced
in the east-west plane, henceforth referred to as out-of-plane.
4.4.1
Bracing frame
A pair of bracing frames were used to brace the MRF and DBF of the test structure in the
out-of-plane direction. These frames were designed for a previous test conducted by
Herrera (2005) and were subsequently modified by Gonner (2009). An elevation of the
48
bracing frames is shown in Figure 4.33. The test structure is braced off of the loading
beam system, which is in turn braced by the bracing frame.
In order to allow placement and removal a previously tested frame the south most two
columns (columns 1 and 2 of Figure 4.33) of the east bracing frame were cut 1 foot above
the lowest beam. In order to test the MRF this had to be repaired. A bolted connection
was designed that would allow this section of the bracing frame to be removed to allow
test frames to be easily installed and removed. Figure 4.34 through Figure 4.37 shows
details of this connection. The connection was design to carry the full axial load and
bending moment of the column.
4.4.2
Loading beam bracing
To brace the loading beams an adjustable plate system was used. This plate system had a
sheet of Teflon® PTFE mounted to each plate where it contacted the loading beam. The
beam also had a sheet of Teflon® PTFE mounted to it. These sheets reduced the friction
between the plate and the beam. Figure 4.38 shows this bracing system. The plates were
able to be adjusted in order to reduce the friction while still allowing the beam to be
braced.
4.4.3
DBF lateral bracing
At each quarter point of the beams of the DBF lateral bracing is provided by the loading
beams and a series of plates. Figure 4.39 shows the locations of these lateral braces and
Figure 4.40 shows the details for the individual braces used to brace the beams. The
columns were braced at each floor level using the detail shown in Figure 4.27. This detail
also served to support the loading beams.
49
4.4.4
MRF lateral bracing
The MRF was laterally braced in a manner similar to that of the DBF. A lateral bracing
layout was developed that would allow the MRF beams to conform to AISC seismic
requirements for lateral bracing of SMRF (AISC 2005b). This included a requirement to
have a supplemental lateral brace at a distance equal to one-half the depth of the beam
away from the RBS. The locations where bracing are provided are shown in Figure 4.41.
The third floor required an additional brace to meet the required minimum unbraced
length due to the smaller beam size at the roof level. Figure 4.42 shows the design of the
1st floor MRF lateral bracing. Similar bracing details were used for the other floors.
4.5 External reactions
In order to transfer applied forces out of the structure and into the reaction floor of the
laboratory two different types of fixtures were used. The first is a column base reaction
fixture. This reaction fixture was attached to the base of each column and served to
remove the axial and shear forces developed in the frame due to overturning moment.
The second type of fixture was a pair of “ground links”. The ground links functioned to
remove the rest of the base shear force at the ground level of the test structure.
4.5.1
Ground links
The test structure had two “ground links” to remove lateral forces near the base. Each
consisted of a clevis and load cell which were attached to the column at the ground floor
as shown in Figure 4.43. The force was then transferred into a W14x257 spreader beam,
which then transferred the force into a pair of braces constructed of back to back angles.
The spreader beam and brace configuration is shown in Figure 4.44. The ground link was
50
originally designed by Herrera (2005) and was later modified by Dong (2013). Details of
this modification appear in Dong (2013).
Prior to the MRF being installed, the ground link load cell and clevis were installed on
the south column of the DBF. A W14x455 column section was installed between the
spreader beam and the ground link load cell, and functioned as a transfer beam. This
extension was then removed to allow that MRF to be installed and the load cell and clevis
portions of the link were moved to the south end of the MRF. The final configuration is
shown in Figure 4.1.
4.5.2
Bay link
To connect the two frames and complete the ground link system a “bay link” needed to
be designed. This section would be subjected to both axial force and end rotation. In
order to reduce the moment associated with this rotation, the moment of inertia of the
section was reduced by orienting a wide flange section on its weak bending axis and then
trimming the flanges. The flanges were only trimmed near the ends to maintain the axial
stiffness of the member near midspan. Figure 4.45 shows the design of the bay link. The
end plates were designed to match the existing hole pattern provided for the ground link.
This member was designed to carry 200 kips of compressive or tensile force and an end
rotation of up to 0.03 radians.
4.6 Rigid Links
During initial DBF characterization, the frame needed to be tested without dampers to
assess the properties of the test setup. In order for the DBF to be stable a set of “rigid
links” had to be put into the frame in place of the dampers. Each link consisted of a HSS
51
pipe section welded to two end plates. These end plates were then bolted into existing
damper clevis attachment. This configuration is shown in Figure 4.46 and Figure 4.47.
52
Table 4.1 - Average measured DBF WF section dimensions and computed section
properties (figure adapted from Lewis 2004)
Section
W12x40
W12x40
W12x40
W12x40
W8x67
W8x67
d
tw
tf
bf
A
Ix
Zx
(in)
(in)
(in)
(in)
(in2)
(in4)
(in3)
Ground Floor
11.88
0.31
0.50
8.00
11.33
291
54.4
Nominal
11.90
0.30
0.52
8.01
11.70
307
57.0
1st Floor
11.88
0.31
0.50
8.00
11.33
291
54.4
Nominal
11.90
0.30
0.52
8.01
11.70
307
57.0
2nd Floor
11.88
0.31
0.50
8.00
11.33
291
54.4
Nominal
11.90
0.30
0.52
8.01
11.70
307
57.0
3rd Floor
11.88
0.31
0.50
8.00
11.33
291
54.4
Nominal
11.90
0.30
0.52
8.01
11.70
307
57.0
South Column
8.89
0.59
0.90
8.16
18.90
253
66.2
Nominal
9.00
0.57
0.94
8.28
19.70
272
70.1
North Column
8.91
0.59
0.90
8.19
18.88
254
66.3
Nominal
9.00
0.57
0.94
8.28
19.70
272
70.1
Location
53
Table 4.2 - Average measured MRF member dimensions and computed section properties
(figure adapted from Lewis 2004)
Section
d
tw
tf
bf
A
Ix
Zx
(in)
(in)
(in)
(in)
(in2)
(in4)
(in3)
Ground Floor
18.03
0.37
0.57
6.00
13.13
671
86.3
Nominal
18.10
0.36
0.61
6.06
13.50
712
90.7
1st Floor
18.03
0.36
0.56
6.00
12.81
658
84.4
Nominal
18.10
0.36
0.61
6.06
13.50
712
90.7
2nd Floor
14.19
0.35
0.47
6.88
11.19
375
60.2
Nominal
14.10
0.31
0.52
6.77
11.20
385
61.5
3rd Floor
10.19
0.26
0.32
3.98
5.06
81
18.6
Nominal
10.10
0.24
0.33
4.01
4.99
82
18.7
South Column
8.89
0.59
0.90
8.16
18.90
253
66.2
Nominal
9.00
0.57
0.94
8.28
19.70
272
70.1
North Column
8.91
0.59
0.90
8.19
18.88
254
66.3
Nominal
9.00
0.57
0.94
8.28
19.70
272
70.1
Location
W18x46
W18x46
W14x38
W10x17
W8x67
W8x67
54
Table 4.3 - Hydraulic actuator specifications (RTMD 2012)
Actuator Type
200-100-1700
200-1000-1250
Quantity
1
2
Load Regulation Accuracy
0.2% FS (but no higher
than 0.23KN)
0.2% FS (but no higher
than 0.17KN)
> 10Hz
> 10Hz
0.2% FS (but no higher
than 0.1mm)
0.2% FS (but no higher
than 0.1mm)
> 10Hz
> 10Hz
Load Capacity
2300KN @ 20.7MPa
1700KN @ 20.7MPa
Speed Capacity
0.84m/s (33in/s)
1.14m/s(45in/s)
Piston Diameter
424mm
378mm
Piston Rod Diameter
200mm
200mm
Stroke
500 mm
500 mm
Total Chamber Volume
114 liters
84 liters
Chamber Internal Leakage
0.15 liters/min/bar
0.15 liters/min/bar
Chamber External Leakage
0.01 liters/min/bar
0.01 liters/min/bar
Load Tracking Dynamic
Bandwidth
Displacement Regulation
Accuracy (Static)
Displacement Tracking
Dynamic Bandwidth
Moving Part Mass (Piston
&
950Kg (approximately)
Rod Assembly)
900Kg (approximately)
Actuator Weight
6100Kg
6120Kg
Actuator Dimension
5.36m —1.25m — 1.35m
(length —width —height)
5.36m —1.25m — 1.35m
(length —width —height)
55
Figure 4.1 – Elevation of bracing frame with DBF and MRF installed
56
Figure 4.2 – Section A-A of Figure 4.1
57
Figure 4.3 – Section B-B of Figure 4.1 (Note DBF Braces Not Shown)
58
Figure 4.4 – Plan View of DBF Test Setup
59
Figure 4.5 – Plan View of MRF Test Setup
60
Figure 4.6- DBF assembly
61
Figure 4.7- DBF in bracing frame
62
Figure 4.8 – Top view of 2nd Floor Beam RBS cut
63
Figure 4.9 – Side View of 2nd Floor Beam End Details
64
Figure 4.10 – MRF 2nd Floor Column with Doubler and Continuity Plates Attached
65
Figure 4.11 – MRF Being Assembled
66
Figure 4.12 – MRF Laid Out on Lab Floor
67
Figure 4.13 – MRF Orientation for Web Weld
68
Figure 4.14- 3rd Floor web before welding
Figure 4.15- 3rd Floor web after welding
69
Figure 4.16- MRF Orientation for Beam Flange Welds
70
Figure 4.17- 2nd Floor Beam Bottom Flange with Run Off Tabs in Place Prior to Welding
Figure 4.18- Ground Floor Beam Bottom Flange with Runoff Tabs in Place Prior to
Welding
71
Figure 4.19- Ground Floor Bottom Flange with Run Off Tabs, Post Welding
72
Figure 4.20- Ground Floor Top Flange with Run Off Tabs, Post Welding
73
Figure 4.21- Ground Floor Top Flange with Run Off Tabs Removed and Weld Ground
74
Figure 4.22 – Actuator Dimensions (Servotest, 2003)
75
Loading Beam
HSS12x12x3/8
Figure 4.23 – Top View of Loading Beam Configuration for DBF Testing
Figure 4.24 – Section A-A of Figure 4.23 (Gonner 2009)
76
Figure 4.25 – Section B-B of Figure 4.23 (Gonner 2009)
Figure 4.26 – Section C-C of Figure 4.23 (Gonner 2009)
77
Loading Beam
Loading Beam
Shelf
Figure 4.27- DBF Column Bracing and Loading Beam Shelves (Dong 2013)
Loading Beam
DBF Beam
78
Figure 4.28 – N-S elevation of DBF Load Attachment
Loading Beam
DBF Beam
Loading Beam
Figure 4.29 – Plan View of DBF Load Attachment
MRF Loading Beam
Figure 4.30- Loading Beam Splice
79
DBF Loading Beam
Loading Beam
Figure 4.31 – Top View of Loading Beam Configuration for MRF Testing
80
Figure 4.32 – MRF Loading Beam Shelf
81
Figure 4.33 – Elevation of Bracing Frame (Herrera 2005)
82
Figure 4.34- Bracing Frame Column Repair (Detail 1 of Figure 4.33) East Elevation
Figure 4.35- Bracing Frame Repair (Detail 1 of Figure 4.33) South Elevation
83
Figure 4.36- Bracing Frame Repair (Cross Section A-A of Figure 4.34, Bracing Frame
Beams Not Shown For Clarity)
84
Figure 4.37- Photograph of bracing frame repair
85
Figure 4.38- Bracing of Loading Beam by Bracing Frame (Gonner 2009)
86
Brace Location
Loading Beam Shelf
Figure 4.39 – Locations of DBF lateral bracing and loading beam shelves
87
Figure 4.40 – Typical DBF lateral bracing
88
Brace Location
Loading Beam Shelf
Figure 4.41- MRF Out-of-Plane Bracing and Loading Beam Shelves
89
Figure 4.42- MRF 1st Floor Beam Lateral Bracing Detail
90
W14x257
Spreader
Beam
DBF
Column
Figure 4.43- Ground Link
91
Figure 4.44- Typical Ground Link Reaction Spreader Beam and Braces (Herrera 2005)
92
Figure 4.45- Bay Link Detail
93
Figure 4.46 Rigid Links (Dong, 2013)
Figure 4.47- DBF assembly
94
Chapter 5.
Instrumentation
5.1 General
This chapter describes the instrumentation installed in the test setup to collect the data
used to evaluate the test structure and testing fixtures. It begins by summarizing the type
and locations of the instrumentation. The determination of member internal forces from
measured data is also discussed. The final portion of this chapter discusses the calibration
of the bay link instrumentation and determination of the axial stiffness of the bay link.
5.2 Description of Instruments
Various types of instruments were used to collect data on the MRF and DBF including
internal full bridge load cells (referred to herein as full-bridges) to measure structural
member moment and axial forces; linear variable differential transducers (LVDT), linear
potentiometers, and temposonics to measure displacements; load pins and load cells to
measure reaction forces; thermo couples used to measure temperature; accelerometers to
measure accelerations; and strain gauges to measure strain in the members. Included in
this section are diagrams of the most common instrumentation configurations. In the
following subsections each instrument type is described as well as its placement in the
MRF and DBF.
5.2.1
Internal full bridge load cells
95
The general full bridge internal load cell layout for each frame consisted of a full bridge
to measure axial force at the mid-height of each story; in addition a pair of full bridges
was also located on each column, one above and one below the axial force full bridge, to
measure moment at these locations. A similar configuration was used on the braces of the
DBF. Since the moment diagram varies linearly in each member the moment diagram
could be determined from the two moment full bridges. An additional axial force full
bridge was located on the section of column below the ground beam to measure the
vertical reaction force at the base of each frame.
Each full bridge consists of 4 single strain gauges wired as a Wheatstone bridge as to
measure either axial strain or bending strain. This strain is then converted to a force or
moment measurement, using calibration factors (the X factors given in Table 5.1). These
factors are based on the theoretical relationship between the full bridge strain output and
either axial force or bending moment. Details are discussed later.
Figure 5.1 shows the locations of the 38 sets of full bridges on the DBF. There are 14
full bridges installed on the DBF to measure axial force, where the strain gauges for each
are wired in the configuration shown in Figure 5.2. Additionally, there are 24 moment
full bridges that are wired in the configuration shown in Figure 5.3. All full bridges used
on the DBF were of 350 ohm resistance. This resistance was selected based on the
availability of 350 ohm data acquisition cards. They also used an excitation voltage of
10V.
Figure 5.4 shows the location of the 20 full bridges on the MRF. Eight of the full bridges
were wired to measure axial force, while the remaining 12 were wired to measure
96
moment. Specific bridge locations on the columns were chosen where the member
remained elastic. This was done to ensure they would continue to function throughout
testing. All MRF full bridges were created using four 120 ohm strain gauges. 120 ohm
gauges were chosen for the MRF instead of 350 ohm gauges due to data acquisition
limitations. The MRF full bridges were excited at 6V instead of the customary 10V due
to current limitations of the data acquisition cards.
It is important to know the force applied to each frame. During initial static and dynamic
testing of the DBF this was accomplished using only the reading from the actuator load
cell. However once the MRF was installed a measure of the force in the loading beams
between each of the two frames was needed. This measurement was obtained using full
bridges on the loading beams that were configured to measure only axial force. A total of
six full bridges were used, with one installed on each loading beam. The gauge was
placed on the portion of loading beam between the two frames. In selecting an exact
location, care was taken to avoid a location that would contact either the MRF or DBF
columns during any test in which the frames were not connected to the loading beams.
This was done in order to ensure that the gauges did not get damaged during testing.
A full bridge strain gauge was installed at the center of the bay link in order to determine
axial force in the link. The location of this full bridge is indicated in Figure 5.5.
All full bridges for the DBF and MRF used the sign convention shown in Figure 5.6
through Figure 5.8.
5.2.2 Full bridge calibration
97
With the exception of the full bridge on the bay link it was not possible to calibrate the
full bridges, due to the cost and difficulty associated with calibrating them. Therefore a
calibration based on theory was used to relate the voltage output of the bridge to the axial
force or moment in the member. The theoretical calibration coefficient needed for
converting voltage to axial force for the wiring configuration in Figure 5.2 is (Dally
1991):
𝑋𝐴 =
2𝐸𝐴
𝑆𝑔 𝑉𝑖𝑛 (1 + 𝜈)
(5-1)
where
𝑋𝐴 = axial full bridge calibration factor without gain, kips/volt
𝐸= Young’s modulus (29000ksi for steel), ksi
A= area of member, inch2
𝑆𝑔 = gauge factor of gauges in circuit
𝑉𝑖𝑛 = excitation voltage of the bridge, Volts
𝜈 = Poisson‘s ratio (0.28 for steel)
Dally also showed that the theoretical calibration coefficient needed for converting
voltage to bending moment for the wiring configuration in Figure 5.3 is:
𝑋𝑚 =
2𝐸𝐼𝑥
𝑑𝑆𝑔 𝑉𝑖𝑛
98
(5-2)
where:
𝑋𝑚 = moment full bridge calibration factor without gain, kip-in/volt
𝐸= Young’s modulus (29000ksi for steel), ksi
𝐼𝑥 = Area of member, in4
𝑑 = depth of the member, in
𝑆𝑔 = gauge factor of gauges in circuit
𝑉𝑖𝑛 = excitation voltage of the strain gauge, V
Lewis (2004) showed in his research that these coefficients can be used to accurately
translate the voltage output of the full bridge to axial forces and moments in large-scale
testing. In order to get an accurate calibration coefficient, measured section dimensions
such as those in Table 4.1 and Table 4.2 were used to calculate these coefficients. A
summary of the calibration factor and excitation voltage used for each full bridge is
presented in Table 5.1.
5.2.3
Load cells and load pins
Figure 5.9 shows the locations of load cells and load pins for the DBF. To measure the
base reaction of the DBF a pair of load pins produced by Strainsert are provided at each
column base where they were inserted into a clevis. Each load pin was calibrated to
measure ± 450 kips of shear force and has a diameter of 3-1/2 inch and a length of 10
inch. Figure 5.10 shows the configuration of the two pins in the clevis. In order to find
the total reaction force at either of the two clevises it is necessary to sum the
99
measurements of the two pins at that clevis. The load pins located at the south end of the
DBF were oriented to measure vertical force while the load pins at the north end of the
DBF were oriented to measure lateral force.
The lateral force carried by the ground links was measured by a load cell at both sides of
the test structure. The locations of these load cells are indicated in Figure 4.1. These load
cells were manufactured by Houston Scientific and have a range of ±600 kips. They are
12 inch long with a diameter of 6 inch, and coupled with a threaded rod on either side.
They were held in place by a pair of tapered collars, which prestressed the load cell and
prevented slip in the threaded rod. Further details of the ground link configuration can be
found in Dong ( 2013).
Load cells are also be provided for each damper. These differ depending on the type of
damper.
5.2.4
Displacement transducers
A combination of LVDTs, temposonics, and linear potentiometers are used to measure
displacements and relative displacements of the two frames and their fixtures.
5.2.4.1 DBF
Figure 5.11 shows the initial placement of displacement transducers used in the DBF.
One-quarter inch stroke LVDTs are used to measure any horizontal axial deformation of
the ground links. In the initial configuration three instruments were used on each ground
link, one measuring the deflection of the spreader beam that transfers the ground link
force to the braces that carry it into the laboratory strong floor and two on either side of
100
the ground link load cell, measuring the load cell axial deformation. It was later
determined that a better configuration was to use two instruments and to measure the
lateral movement of the column flanges at the center of the ground link. This
configuration appears in Figure 5.12.
During MR damper testing, linear potentiometers were used to measure damper
displacement, (i.e. the stroke of the damper), because they are less susceptible to the
interference caused by the damper’s magnetic field. For testing using other damper types,
LVDTs will be used to measure damper displacement because linear potentiometers have
more noise due to any variation in supply current. To measure damper displacement an
instrument with ±3 inch of stroke was used. During initial testing LVDTs were installed
to measure axial deformation of the rigid links. These instruments were installed on either
side of the rigid link tube as shown in Figure 5.13.
The displacement of each floor of the DBF and MRF relative to the bracing frame was
measured by a displacement transducer mounted at the middle of each bay. This
transducer was mounted to the top flange of the beam as shown in Figure 5.14. The
decision to mount the instrument on the top flange was to mimic the node location in
previously produced computer models. During initial characterization of the structure
short range LVDTs were used to measure the first and second floor displacement as these
provided more accurate reading over the smaller displacements that the frame was
subjected to. Once a damper was installed, the frame was subjected to larger lateral
displacements, so longer range linear potentiometers and temposonics were used instead.
Linear potentiometers were used in locations near where an MR damper was installed to
101
prevent any possible electronic interference. The decision to used temposonics instead of
LVDTs was due to the availably of more long range temposonics.
Axial deformation and rotation of the T-connection were determined using four-½ inch
range LVDTs (± ½ inch) arranged in the configuration shown in Figure 5.15. The
average of the four sensors was used to measure the deformation across the T-connection.
Rotation reported in radians was determined using the following formula:
𝜃=
∆𝑡𝑜𝑝 − ∆𝑏𝑡𝑚
𝑑𝐿𝑉𝐷𝑇
(5-3)
where,
𝜃 = rotation across T-connection (radians)
∆𝑡𝑜𝑝 = average deformation of top flange LVDTs
∆𝑏𝑡𝑚 = average deformation of bottom flange LVDTs
𝑑𝐿𝑉𝐷𝑇 = distance between LVDTs
5.2.4.2 MRF
Figure 5.16 shows the locations of displacement transducers on the MRF. To measure
horizontal floor displacements, linear temposonics are mounted at mid bay. These will
measure the floor displacement relative to the bracing frame. This configuration is the
same as that shown in Figure 5.14. The third floor uses a 44 inch (± 22 inch), while the
other two floors use 30 inch (± 15 inch) temposonics to allow testing to over 6% story
102
drift. The ground floor will have a 1-inch range LVDT (± 1 inch) mounted in a similar
manner to that shown in Figure 5.14.
At the RBS sections a set of 4 LVDTs are used to measure rotation as well as axial
deformation in the RBS. The instruments will be mounted on the inside of the flanges,
two LVDTs on the top flange on either side of the web and two LVDTs on the bottom
flange on either side of the web, as shown in Figure 5.17. This configuration is similar to
that used to measure the axial deformation of the T-connections in the DBF. Equation
(5-3) will be used to determine the rotation in radians. Sizing of these instruments is
based on expected plastic rotation of up to 3% radians within the RBS. Accounting for
the depth the shallower third floor beams requires a ½ inch range LVDTs (± ½ inch),
while the other stories with deeper W14 and W18 beams require 1 inch range LVDTs (±
1 inch).
The deformation of the MRF south ground link will be measured with two-¼ inch range
LVDTs (± ¼ inch) mounted on each side of the column, which will measure lateral
displacement at the ground link column interface relative to the ground. This
configuration is the same as on the DBF north ground link.
Two ¼ inch range LVDTs (± ¼ inch) will be fixed to either side of each column base
plate to measure column uplift. This uplift is important to know because it could indicate
slop in the load pins supporting the column.
5.2.4.3 Other displacements and deformations
103
The deformation of the bay link will be measured in a similar manner, with two - ¼ inch
range LVDTs (± ¼ inch) mounted to the column on either side of the link, but instead of
using a fixed reference point on the ground, the LVDT will measure relative
displacement between the MRF and DBF inner columns. Figure 5.5 shows the placement
of the bay link displacement transducers.
5.2.5
Strain gauges
Figure 5.18 shows the single strain gauge locations for the DBF. Strain gauges were
placed in areas that were deemed critical and likely to yield during testing. To determine
which locations were most likely to yield, structural analysis were conducted. Areas
where strain gauges were located include the first and third story gusset plates connecting
the beams to the braces, the column flanges at the bottom of the structure, and the first
story braces. It was determined that the second story braces and gussets were unlikely to
yield before the other stories so these did not receive gauges. All strain gauges on the
DBF were 350-ohm strain gauges with a range of ± 3 percent.
Figure 5.19 shows the location of strain gauges for the MRF. Two different types of
strain gauges were installed on the MRF. The first kind are rosette strain gauges. These
gauges were installed in the panel zones and measure strain vertically, horizontally and
45° diagonally. A rosette was installed on both sides of each floor’s panel zone.
Additionally strain gauges were installed within the RBS section to measure deformation.
Two gauges were installed on the outside of each flange and two gauges were installed
on each side of the web of the beam, for a total of 8 strain gauges per RBS.
104
Figure 5.22Figure 5.20 through Figure 5.21 show the layout of these strain gauges at the
first, second and third floors, respectively. All MRF strain gauges are of a 120 ohm
resistance.
5.2.6
Accelerometers
Figure 5.23 shows the locations of 7 accelerometers used to measure frame accelerations
of the DBF. These accelerations were needed as feedback signals for various MR damper
control laws. The accelerometers located on the columns were attached to the outer
flange of the north column in line with each floor. The three accelerometers located on
the braces were attached to the lower brace gusset as shown in Figure 5.23 and measured
horizontal brace accelerations. One accelerometer was located at midbay on the ground
floor beam. All accelerometers were single axis accelerometers manufactured by Kistler
which were capable of measuring ± 3g’s and measured accelerations in the North-South
direction as indicated in Figure 5.23.
5.3
Determination of Internal Force from Instrumentation
One objective of the instrumentation of the two frames was to measure internal member
forces, frictional forces and reactions during a test. Whenever it was practical, the force
was directly measured via load cells or full bridges. The following describes how
member forces are obtained that are not directly measured.
5.3.1
Column and brace shears
Axial forces and moments in the columns and braces were directly measured. Using the
moment measured from two full bridges on a single member and the free body diagram
105
shown in Figure 5.24 it was possible to determine the member shear force, V, from statics
where:
𝑉=
where,
𝑀2 − 𝑀1
𝑑
(5-4)
V= Shear in column
𝑀1 = Moment output of lower full bridge
𝑀2 = Moment output of upper full bridge
d= distance between full bridges
5.3.2
Beam internal forces
The internal forces in the beams of the DBF can be determined using measured moments
and axial forces from the column and brace full bridges. Considering the free body
diagram shown in Figure 5.25 for the DBF, the shear 𝑉𝐵 , axial force 𝑃𝐵 and moment 𝑀𝐵
in the beam can be obtained by statics using the following three equations:
𝑉𝐵 = 𝐹𝐿𝐶 − 𝐹𝑈𝐶 + 𝑐𝑜𝑠𝜃 ∗ 𝐹𝐵𝑅 − 𝑠𝑖𝑛𝜃 ∗ 𝑉𝐵𝑅
(5-5)
𝑀𝐵 = −𝑉𝑈𝐶 ∗ 𝐻𝑈𝐶 − 𝑉𝐿𝐶 ∗ 𝐻𝐿𝐶−𝑉𝐵 ∗ 𝐿 − 𝑉𝐵𝑅 ∗ 𝐿𝐵𝑅 − 𝑀𝑈𝐶 + 𝑀𝐿𝐶 + 𝑀𝐵𝑅
(5-7)
𝐹𝐵 = −𝑉𝐿𝐶 + 𝑉𝑈𝐶 − 𝑠𝑖𝑛𝜃 ∗ 𝐹𝐵𝑅 − 𝑐𝑜𝑠𝜃 ∗ 𝑉𝐵𝑅
106
(5-6)
where the column (𝑉𝐿𝐶 , 𝑉𝑈𝐶 ) and brace (𝑉𝐵𝑅 ) shears were determined using Equation
(5-4). To determine the forces in the MRF beams, the brace terms in the above equations
are set to zero. A free body of this configuration is shown in Figure 5.26.
5.3.3
Story shear
There are several instances where story shear will be a useful quantity to know during
testing, including assessing friction in the test setup. In order to determine story shear a
horizontal cut through the structure at a floor is made and the story shear is obtained from
statics.
5.3.4
Friction on test structure
The free body diagram in Figure 5.27 shows static lateral forces applied to the DBF
where the MRF is not connected to the loading beams. In order to assess the amount of
3rd story friction in the due to friction the free body diagram in Figure 5.28 was used in
which the frame has been cut through the third story. A story shear could be derived by
summing the horizontal components of the brace axial and shear force and adding those
to the column shear force. Then by summing lateral forces the magnitude of the 3rd story
friction force could be determined. To find the 2nd story friction force the free body in
Figure 5.29 was used in a similar manner, only this time the now known 3rd story friction
force is considered. Once the 2nd story friction force is solved for the 1st story friction
force is found using the free body diagram in Figure 5.30.
Figure 5.31 shows the lateral forces applied to the MRF from the loading beams. Friction
will be determined following the procedure specified for determining friction force in the
DBF, by where the friction force will be found in each floor by comparing the measured
107
applied load to the measured story shear. To determine the friction in the 3rd story the free
body diagram in Figure 5.32 will be used. By setting the sum of these forces equal to zero
the friction force is solved for. In a similar manner the free body in Figure 5.33 will be
used to assess the friction force in the second story and the free body in Figure 5.34 to
assess the friction force in the first floor.
5.4 Calibration of the Bay Link Full Bridge
The full bridge on the bay link was calibrated in order to determine the relationship
between bridge output voltage and axial force in the link. Calibration was done using a
2670 kN Sactec universal test machine. The link was subjected to 75kips of compressive
force. The voltage change and deformation during the test was recorded. This calibration
was repeated twice.
An excitation voltage of 6V used to measure voltage change in the full bridge on the bay
link. Voltages were manually read using a volt meter and recorded every 7.5kips. The
relationship between voltage change and axial force was then used to establish the
calibration constant. A plot of this relationship appears in Figure 5.35. This calibration
constant is included in Table 5.1.
108
Table 5.1 – Full bridge inputs
Name
Type
Location
X Factor
Input
Voltage
(V)
X Factor
Units
FB1
Moment
DBF First Story Column
82818
10
kip-in/volt
FB2
Axial
DBF First Story Column
41853
10
kip/volt
FB3
Moment
DBF First Story Column
82818
10
kip-in /volt
FB4
Moment
DBF Second Story Column
82818
10
kip-in/volt
FB5
Axial
DBF Second Story Column
41853
10
kip/volt
FB6
Moment
DBF Second Story Column
82818
10
kip-in/volt
FB7
Moment
DBF Third Story Column
82818
10
kip-in/volt
FB8
Axial
DBF Third Story Column
41853
10
kip/volt
FB9
Moment
DBF Third Story Column
82818
10
kip-in/volt
FB10
Moment
DBF First Story Column
82818
10
kip-in/volt
FB11
Axial
DBF First Story Column
41853
10
kip/volt
FB12
Moment
DBF First Story Column
82818
10
kip-in/volt
FB13
Moment
DBF Second Story Column
82818
10
kip-in/volt
FB14
Axial
DBF Second Story Column
41853
10
kip/volt
FB15
Moment
DBF Second Story Column
82818
10
kip-in/volt
FB16
Moment
DBF Third Story Column
82818
10
kip-in/volt
FB17
Axial
DBF Third Story Column
41853
10
kip/volt
FB18
Moment
DBF Third Story Column
82818
10
kip-in/volt
FB19
Axial
DBF First Story Brace
19057
10
kip/volt
FB20
Moment
DBF First Story Brace
23173
10
kip-in/volt
FB21
Moment
DBF First Story Brace
23173
10
kip-in/volt
FB22
Moment
DBF First Story Brace
23173
10
kip-in/volt
FB23
Moment
DBF First Story Brace
23173
10
kip-in/volt
FB24
Axial
DBF First Story Brace
19057
10
kip/volt
FB25
Axial
DBF Second Story Brace
19057
10
kip/volt
FB26
Moment
DBF Second Story Brace
23173
10
kip-in/volt
109
Name
Type
Location
X Factor
Input
Voltage
(V)
X Factor
Units
FB27
Moment
DBF Second Story Brace
23173
10
kip-in/volt
FB28
Moment
DBF Second Story Brace
23173
10
kip-in/volt
FB29
Moment
DBF Second Story Brace
23173
10
kip-in/volt
FB30
Axial
DBF Second Story Brace
19057
10
kip/volt
FB31
Axial
DBF Third Story Brace
19057
10
kip/volt
FB32
Moment
DBF Third Story Brace
23173
10
kip-in/volt
FB33
Moment
DBF Third Story Brace
23173
10
kip-in/volt
FB34
Moment
DBF Third Story Brace
23173
10
kip-in/volt
FB35
Moment
DBF Third Story Brace
23173
10
kip-in/volt
FB36
Axial
DBF Third Story Brace
19057
10
kip/volt
FB37
Axial
DBF Ground Floor Column
41853
10
kip/volt
FB38
Moment
MRF First Story Column
132635
6
kip-in/volt
FB39
Moment
MRF First Story Column
132635
6
kip-in/volt
FB40
Moment
MRF First Story Column
68585
6
kip/volt
FB41
Moment
MRF First Story Column
132635
6
kip-in/volt
FB42
Moment
MRF Second Story Column
132635
6
kip-in/volt
FB43
Axial
MRF Second Story Column
68585
6
kip/volt
FB44
Moment
MRF Second Story Column
132635
6
kip-in/volt
FB45
Moment
MRF Third Story Column
132635
6
kip-in/volt
FB46
Axial
MRF Third Story Column
68585
6
kip/volt
FB47
Moment
MRF Third Story Column
132635
6
kip-in/volt
FB48
Moment
MRF First Story Column
132635
6
kip-in/volt
FB49
Axial
MRF First Story Column
68585
6
kip/volt
FB50
Moment
MRF First Story Column
132635
6
kip-in/volt
FB51
Axial
MRF Second Story Column
132635
6
kip/volt
FB52
Moment
MRF Second Story Column
68585
6
kip-in/volt
FB53
Moment
MRF Second Story Column
132635
6
kip-in/volt
110
Name
Type
Location
X Factor
Input
Voltage
(V)
X Factor
Units
FB55
Axial
MRF Third Story Column
132635
6
kip/volt
FB56
Moment
MRF Third Story Column
68585
6
kip-in/volt
FB57
Axial
MRF Ground Story Column
132635
6
kip/volt
FB58
Axial
MRF Ground Story Column
68585
6
kip/volt
FB59
Axial
First Story Loading Beam
68585
6
kip/volt
FB60
Axial
First Story Loading Beam
59236
6
kip/volt
FB61
Axial
Second Story Loading Beam
59236
6
kip/volt
FB62
Axial
Second Story Loading Beam
59236
6
kip/volt
FB63
Axial
Third Story Loading Beam
59236
6
kip/volt
FB64
Axial
Third Story Loading Beam
59236
6
kip/volt
FB65
Axial
Bay Link
17161
6
kip/volt
111
Figure 5.1 – DBF Full Bridge Locations
112
Figure 5.2 – Axial Force Full Bridge Geometry and Wiring Schematic
113
Figure 5.3 – Bending Moment Full Bridge Geometry and Wiring Schematic
114
Figure 5.4 – MRF Column Full Bridge Locations
115
Figure 5.5 – Bay Link Instrumentation
116
Figure 5.6 – MRF and DBF Column Axial Force and Moment Sign Convention
Figure 5.7 – DBF South Brace Axial Force and Moment Sign Convention
Figure 5.8 – DBF North Brace Axial Force and Moment Sign Convention
117
Figure 5.9 – DBF Load Cell Locations
118
Figure 5.10 – Ground Link Load Cell
119
Figure 5.11 – Location of DBF Displacement Transducers
120
Figure 5.12 – Ground Link Displacement Transducer Plan
Figure 5.13 – Rigid Link Displacement Transducer
121
Figure 5.14 – DBF Floor Displacement Transducer
122
Figure 5.15 – DBF T-Connection LVDT Placement
123
Figure 5.16 – MRF Displacement Transducer Locations
124
Figure 5.17 – RBS LVDT Placement
125
Figure 5.18 – DBF Strain Gauge Locations
126
Figure 5.19 – MRF Strain Gauge Locations
127
Top View of Beam Flange
Figure 5.20 – MRF 1st Floor Strain Gauge Locations
128
Top View of Beam Flange
Figure 5.21 – MRF 2nd Floor Strain Gauge Locations
Top View of Beam Flange
Figure 5.22 – MRF 3rd Floor Strain Gauge Locations
129
Figure 5.23 – DBF Accelerometer Locations
130
Figure 5.24 – Free Body Diagram Used to Solve Column and Brace Moments (Forces
Shown Acting Positive Sense)
131
Figure 5.25 – Typical Free Body Diagram Used to Calculate DBF Beam Forces, and
Diagonal Brace and Column Shear Forces (Forces Shown Acting Positive Sense)
132
Figure 5.26 – Typical Free Body Diagram Used to Calculate MRF Beam Forces and
Column Shear Forces (Forces Shown Acting Positive Sense)
133
DBF 3rd Story Friction Force
DBF 3rd Story Friction Force
DBF 2rd Story Friction Force
DBF 2rd Story Friction Force
DBF 1st Story Friction Force
DBF 1st Story Friction Force
DBF South Groundlink Force
DBF South Groundlink Force
DBF North Base
Lateral Force
DBF South Base
Lateral Force
Figure 5.27 – DBF External Lateral Force Diagram
134
Figure 5.28 - 3rd Story DBF Freebody Diagram
DBF 3rd Story Friction Force
Actuator 3 Force
DBF 2rd Story Friction Force
Actuator 2 Force
DBF 2nd
Story Shear
Figure 5.29 – 2nd Story DBF Freebody Diagram
135
DBF 3rd Story Friction Force
Actuator 3 Force
DBF 2rd Story Friction Force
Actuator 3 Force
DBF 1st Story Friction Force
Actuator 1 Force
DBF 1st
Story Shear
Figure 5.30 – 1st Story DBF Freebody Diagram
136
1
Figure 5.31 – MRF External Lateral Forces
137
Figure 5.32 - Free Body Diagram Used to Determine 3rd Story MRF Friction
Figure 5.33 – Free Body Diagram Used to Determine 2nd Story MRF Friction
138
1
Figure 5.34 – Free Body Diagram Used to Determine 1st Story MRF Friction
139
80
Data
70
Trendline
60
17.16 kips/mv
Force (kips)
50
1
40
30
20
10
0
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
Voltage Output (mV)
Figure 5.35 - Bay Link Calibration Force vs Voltage Output
140
1
1.5
Chapter 6.
Damped Brace Frame Characterization Testing
6.1 General
In order to conduct hybrid testing using the DBF, the initial elastic lateral stiffness of the
frame needs to be known. The types of DBF characterization tests conducted, their
purpose and results are discussed in this chapter. Also discussed are modifications made
to both the test fixtures and the DBF as a result of this testing.
6.2 Testing Methodologies
In order to assess various characteristics of the DBF several different types of
characterization tests were conducted. These included quasi-static tests (commonly
referred to as static test), slow predefined sinusoidal displacement tests, and sinusoidal
tests at rates of up to 1 Hz. In total, 84 characterization tests were conducted. Much of the
testing was repeated with different instrument configurations to assess different frame
components. Testing was also conducted both before and after adjustments were made to
test fixtures and the DBF.
6.2.1
Quasi-static testing
Quasi-static tests were performed to measure the stiffness of the DBF and to evaluate the
behavior of individual frame components. The DBF flexibility matrix was derived from
data obtained from the quasi-static tests involving three actuators (discussed later).
During quasi-static testing each floor was loaded individually with a known force, while
141
the other two floors were allowed to displace with no force being applied. This testing
was used with the frame in several different configurations. The first being an individual
actuator attached to the frame at a single floor and the rigid links attached, the second
being three actuators attached to the frame and the rigid links attached, and the third
being three actuators attached, one MR damper in the frame, and the rigid links detached
at the remaining floors.
A model of the frame, constructed by Dong (2013), was used to determine the level of
force required to produce first yielding in the frame. Roughly half of the force needed to
provide first yield was the used in static testing. This was deemed sufficiently high
enough to allow an accurate measurement of the stiffness to be made while remaining
low enough to not damage (yield) the frame. Forces were calculated for two different
frame arrangements, the first with the rigid links attached and the second without the
rigid links attached. Table 6.1shows the forces that were applied to the frame for both
rigid link configurations.
Quasi-static tests were conducted several times during frame characterization, including
quasi-static tests that loaded the frame at the third floor. Loading at the third floor
engaged the T-section connections at all floors in the DBF whereas loading at another
floor only engaged some of the T-section connections. Table 6.2 shows all quasi-static
tests completed as of the writing of this thesis.
Data from quasi-static tests were sampled at 128 Hz in order to decrease the size of data
files associated with these tests. Due to the relatively low velocity during testing this
produced sufficiently dense data plots.
142
6.2.2
Sinusoidal tests
During sinusoidal tests each floor was displaced under displacement control by a
predefined displacement history. In order to determine appropriate displacement
amplitudes for the testing a displacement pattern of the first mode shape floor
displacements were taken and scaled to a level that would not produce yielding in the
DBF. The scaled amplitudes for frame configurations can be found in Table 6.3. A
haversine function was used to provide two ramp-up cycles and two ramp-down cycles.
A plot of the three story displacements for a test without the rigid links is shown in
Figure 6.1. Sinusoidal testing was limited to frequencies of no more than 1Hz in order to
avoid inertial effects.
Sinusoidal tests are important because that they subjected the DBF to dynamic loading.
Since the frame would be tested dynamically it was felt that this would allow any issues
in fixtures that only occurred when the frame was loaded dynamically to be observed.
Data from sinusoidal tests were sampled at 1024 Hz in order to capture as much detail as
possible.
6.3 Friction Force Assessment
It is important to assess the amount of external friction in the test setup because it could
impact that amount of force that was being transferred to the test specimen and the results
of the test. The most likely source of friction is between the loading beams and the
external bracing frame. This bracing is shown in Figure 4.4 and Figure 4.5. If it was
determined if friction is an issue the plates bracing the loading beams would be adjusted
143
outward as described in Section 4.4.2. The method for analyzing the amount of friction
developed on the test setup is discussed in Section 5.3.4.
Figure 6.2 through Figure 6.4 show the results of a friction force analysis for a sinusoidal
test. The maximum friction force developed in the test setup was 2% of the applied
actuator loads. It was concluded from this test and others like it that the amount of
friction force was negligible and the Teflon® plates do not have to be adjusted. The level
of friction however will be checked periodically to determine if anything changed.
6.4 DBF Stiffness Matrix
The three by three stiffness matrix associated with the lateral degree of freedom at each
floor of the DBF was experimentally acquired. These degrees of freedom are shown in
Figure 6.5. The stiffness matrix is valuable for a variety of reasons including evaluation
of the accuracy and calibration of finite element models of the DBF; design of MR
damper control laws and actuator control algorithms, and for use in real time hybrid
simulation. Another use for the stiffness matrix is to help determine if the frame is
damaged during testing. By comparing stiffness matrices of the frame before and after a
test it would be possible to determine whether the frame stiffness had changed. If it had
changed it would be an indication that the frame sustained some sort of damage and
further investigation of the frame would be needed to understand what specific damage
occurred.
6.4.1
Development of stiffness matrix
To develop the stiffness matrix first the flexibility matrix was found from the measured
response. As established by structural theory, flexibility coefficients are the displacement
144
at degree of freedom i due to a unit force applied at degree of freedom j (Hibbler, 2011).
By systematically applying a known actuator force at a single degree of freedom of the
DBF at a time it is possible to determine the full 3x3 flexibly matrix, where the flexibility
coefficients are obtained using the following formula:
𝑓𝑖𝑗 =
∆𝑚𝑎𝑥 − ∆𝑚𝑖𝑛
𝐹𝑚𝑎𝑥 − 𝐹𝑚𝑖𝑛
(6-1)
where,
𝑓𝑖𝑗 = flexibility coefficient (e.g. displacement at DOF i due to a unit force at DOF
j)
∆𝑚𝑎𝑥 = maximum displacement at DOF i
∆𝑚𝑖𝑛 = minimum displacement at DOF i
𝐹𝑚𝑎𝑥 = force at DOF j associated with maximum displacement
𝐹𝑚𝑖𝑛 = force at DOF j associated with minimum displacement
Due to hysteresis a slope was found for both the loading and unloading curve and an
average of the two slopes was taken. This procedure was done for the coefficient
established from Figure 6.6, and the resulting flexibility is plotted in addition to the data.
Using a set of three tests (loading one floor at a time), nine flexibility coefficients are
determined. They were then placed in a 3x3 matrix. An example of a flexibility matrix
for the October 3, 2011 set of static tests (See Table 6.2) is shown in Table 6.5. Once this
flexibility matrix was produced it is inverted to find the DBF stiffness matrix, and is
145
given in Table 6.6. Table 6.7 shows the DBF stiffness matrix where the off diagonal
terms are averaged to make it symmetric.
6.5 Evaluation and Modification of Frame Components
One of primary goals of characterization of the DBF frame was to update finite element
models of the frame which would be used to plan future testing and for parametric studies
after the completion of the laboratory phase of testing. With this goal in mind it is
important to understand the force deformation behavior of many of the frame components
that are unique to this structure and could not initially be accurately modeled. This
included the T-sections, the rigid links and the ground links. After initial testing
nonlinearities were observed in the T-sections and the ground links, so these components
were modified.
6.5.1
T-section connection modifications
The original goal of the T-section beam connection, as discussed in Section 3.4 and
shown in Figure 3.14 was to allow for a pinned connection that would limit the moment
developed within the gusset plate region. In order to avoid slipping in the T-section
connection a set of tapered pins were used in addition to bolts. However during initial
testing it became clear that this connection was not functioning as originally intended and
that slip was occurring. This slip caused significant nonlinearities in the floor
displacement response.
In order to correct the nonlinearity, the bolts of one side of the T-connection were
removed and that side of the connection was welded with a single vertical fillet weld,
which was sized to carry the moment developed in the connection. Figure 6.7 shows this
146
modification. Figure 6.8 shows the results of a static test of the third floor before and
after this modification was made. It is clearly evident that this modification improved the
linearity in the response.
The axial force deformation and moment rotation behavior of the modified T-section
connections from each floor are shown in Figure 6.9 through Figure 6.14. The ground
floor T-section connection response was not measured and was assumed to be similar to
the other floors.
6.5.2
Tightening of rigid link bolts
Another source of nonlinearity in testing was the rigid links placed in the frame before
the dampers were installed. These tubes, shown previously in Figure 4.46, are installed in
place of dampers in the diagonal brace-to-beam connection. LVDTs were temporarily
installed on these links to measure the force-deformation response of each link. It was
determined that there was bolt slip occurring in the rigid links. The bolts used to attach
the rigid links to the south end clevis were tightened and this reduced the slip. The
change to overall floor displacement response due to this modification is show in Figure
6.15. However the rigid link response remained slightly nonlinear, and it was felt it was
not possible to entirely remove this nonlinearity so it was simply included in future frame
models. Figure 6.16 through Figure 6.18 show the axial force deformation behavior of
each of the rigid links.
6.5.3
Ground links
147
Another component that was characterized was the true stiffness of the ground links.
Figure 6.19 and Figure 6.20 shows the axial force-deformation behavior obtained for the
south and north ground links, respectively.
6.5.4 Bay link
The bay link axial stiffness was determined during the calibration of the bay link full
bridge as described in Section 5.4. Axial force-deformation data is plotted in Figure 6.21.
The slope of the data was determined and used as the stiffness of the bay link. Data below
20 kips of compressive force was disregarded because it was assumed that this much
force was required to properly seat the specimen in the test fixture. This stiffness was
then used in all subsequent models that included both frames.
6.6 Application of Stiffness Matrix for Real-time Hybrid Simulation
Hybrid simulation results from two earthquakes were compared to numerical simulations
using the stiffness matrix as a model of the stiffness of the DBF. These hybrid
simulations and numerical simulations were conducted by Philips (2012) with one
physical MR damper in the DBF, an analytical MRF and analytical lean-on-column.
Information on the damper model used for the numerical simulations can be found in
Philips and Spencer (2011).
A comparison between the story displacements of the
numerical simulations and the hybrid simulations involving the ground motions from the
NS component of the Imperial Valley Irrigation District substation in El Centro,
California recorded during the El Centro Earthquake of May 18th, 1940 are shown in
148
Figure 6.22 through Figure 6.24. Good agreement between the numerical and hybrid
simulations results can be seen.
149
Table 6.1– Static Testing Applied Loads
Floor
Applied Load (kN)
With Rigid Links
Without Rigid Links
st
1
2nd
220
180
225
125
3rd
180
90
150
Table 6.2 – Quasi-Static Test Matrix
Test #
Date
Frame Configuration
Floor
Tested
Applied
Load (Kn)
1
2
3
6/14/2011
6/14/2011
6/14/2011
Rigid Links, One Actuator 1st Floor
Rigid Links, One Actuator 1st Floor
Rigid Links, One Actuator 1st Floor
1st Floor
1st Floor
1st Floor
110
220
220
4
5
6
8
9
10
6/24/2011
6/24/2011
6/24/2011
6/30/2011
6/30/2011
6/30/2011
Rigid Links, One Actuator 2nd Floor
Rigid Links, One Actuator 2nd Floor
Rigid Links, One Actuator 2nd Floor
Rigid Links, One Actuator 3rd Floor
Rigid Links, One Actuator 3rd Floor
Rigid Links, One Actuator 3rd Floor
2nd Floor
2nd Floor
2nd Floor
3rd Floor
3rd Floor
3rd Floor
90
180
180
90
90
180
11
12
13
14
15
16
6/30/2011
8/8/2011
8/8/2011
8/8/2011
8/8/2011
8/9/2011
Rigid Links, One Actuator 3rd Floor
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
3rd Floor
3rd Floor
3rd Floor
3rd Floor
3rd Floor
3rd Floor
180
180
180
180
65
180
17
19
20
21
23
24
8/9/2011
8/10/2011
8/10/2011
8/10/2011
8/10/2011
8/10/2011
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
3rd Floor
1st Floor
2nd Floor
3rd Floor
3rd Floor
3rd Floor
180
220
180
180
180
180
25
26
27
28
29
30
8/22/2011
8/22/2011
8/23/2011
8/24/2011
9/21/2011
9/26/2011
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
3rd Floor
3rd Floor
3rd Floor
3rd Floor
3rd Floor
3rd Floor
180
180
180
180
180
180
31
32
33
34
10/3/2011
10/3/2011
10/3/2011
10/24/2011
1st Floor
2nd Floor
3rd Floor
3rd Floor
220
180
180
180
35
2/21/2012
3rd Floor
90
36
2/22/2012
3rd Floor
90
37
2/22/2012
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
Rigid Links, Three Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
3rd Floor
90
151
Test #
Date
39
2/27/2012
41
2/27/2012
42
2/27/2012
44
2/28/2012
45
3/3/2012
46
3/3/2012
47
3/3/2012
Frame Configuration
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
No Rigid Links, 1st Floor MR Damper, Three
Actuators
152
Floor
Tested
Applied
Load (Kn)
2nd Floor
125
3rd Floor
90
3rd Floor
90
1st Floor
225
1st Floor
225
2nd Floor
125
3rd Floor
90
Table 6.3 – Sinusoidal Tests Applied Displacements
Floor
st
1
2nd
3rd
Predefined Sine Wave Amplitude (mm)
With Rigid Links
8
5
2.5
153
Without Rigid Links
50
27
9
Table 6.4 – Sinusoidal Test Matrix
Test #
Date
Frame Configuration
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
10/3/2011
10/3/2011
10/3/2011
10/11/2011
10/3/2011
10/24/2011
10/24/2011
10/24/2011
10/24/2011
11/15/2011
11/15/2011
2/7/2012
2/7/2012
2/7/2012
2/7/2012
2/8/2012
2/16/2012
2/17/2012
2/17/2012
2/17/2012
2/21/2012
2/21/2012
2/23/2012
2/23/2012
2/2/2012
2/27/2012
2/27/2012
2/27/2012
2/29/2012
3/2/2012
3/2/2012
3/6/2012
3/7/2012
3/9/2012
3/9/2012
3/29/2012
3/29/2012
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
Rigid Links
st
1 Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
1st Floor MR Damper
154
Frequency
(Hz)
1
1
0.01
0.1
0.5
1
1
1
1
1
1
0.1
0.03
0.02
0.02
0.0167
0.0167
1
1
1
0.0167
0.0167
0.0167
0.0167
0.0167
1
0.0167
0.5
1
1
1
1
1
1
1
1
1
Table 6.5 – Flexibility Matrix of DBF from Tests 31, 32 and 33 (see Table 6.2)
DOF 1
DOF 2
DOF 3
DOF 1
0.00226 in/kip
0.00238 in/kip
0.00250 in/kip
DOF 2
0.02440 in/kip
0.00478 in/kip
0.00506 in/kip
DOF 3
0.00253 in/kip
0.00511 in/kip
0.00822 in/kip
Table 6.6 – Stiffness Matrix of DBF from Tests 31, 32 and 33 (see Table 6.2)
DOF 1
DOF 2
DOF 3
DOF 1
953.11 kip/in
-478.75 kip/in
4.90 kip/in
DOF 2
-515.31 kip/in
871.05 kip/in
-379.60 kip/in
DOF 3
26.81 kip/in
-394.40 kip/in
356.41 kip/in
Table 6.7 – Off-Diagonal Averaged Stiffness Matrix of DBF from Tests 31, 32 and 33
(see Table 6.2)
DOF 1
DOF 2
DOF 3
DOF 1
953.11 kip/in
-497.03 kip/in
15.85 kip/in
DOF 2
-497.03 kip/in
871.05 kip/in
-386.98 kip/in
DOF 3
15.85 kip/in
-386.98 kip/in
356.41 kip/in
155
Figure 6.1 - DBF 1Hz Sinusoidal Test Displacements
156
Time (Sec.)
Figure 6.2 - Example 1st Story Friction Force Analysis Sinusoidal Test #11
Time (Sec.)
Figure 6.3 - Example 2nd Story Friction Force Analysis Sinusoidal Test #11
157
Time (Sec.)
Figure 6.4 - Example 3rd Story Friction Force Analysis Sinusoidal Test #11
158
Figure 6.5 - DBF Stiffness Matrix Degrees of Freedom
159
Figure 6.6 - Typical Force-Displacement Graph Used in Determining Flexibility
Coefficients
160
tapered pins
Figure 6.7 - T-Connection Modifications
161
Figure 6.8 - Static Test Results Loading at 3rd Floor Before and After T- Connection
Modification
162
Figure 6.9 – 1st floor T-Connection Moment Rotation Behavior
Figure 6.10 – 2nd floor T-Connection Moment Rotation Behavior
163
Figure 6.11 – 3rd floor T-Connection Moment Rotation Behavior
Figure 6.12 – 1st Floor T-Connection Axial Force vs Deformation
164
Figure 6.13 – 2nd Floor T-Connection Axial Force vs Deformation
Figure 6.14 – 3rd Floor T-Connection Axial Force vs Deformation
165
Figure 6.15 - Static Test Results Loading at 3rd Floor Before and After Tightening Rigid
Links
166
Figure 6.16 - 1st Story Rigid Link Axial Force-Deformation Behavior
Figure 6.17 - 2nd Story Rigid Link Axial Force-Deformation Behavior
167
Figure 6.18 - 3rd Story Rigid Link Axial Force-Deformation Behavior
Figure 6.19 - South Ground Link Axial Force-Deformation Behavior
168
Figure 6.20 - North Ground Link Axial Force-Deformation Behavior
169
80
Data
Trendline
70
60
Force (kips)
50
1498 kips/in
40
1
30
20
10
0
0
0.02
0.04
0.06
0.08
Head Travel (in)
Figure 6.21– Bay Link Calibration Force-Head Travel Response
170
0.1
Figure 6.22 - Comparison of 1st Story Displacements for NS Component of the El Centro
Ground Motion
Figure 6.23 - Comparison of 2nd Story Displacements for NS Component of the El Centro
Ground Motion
171
Figure 6.24 - Comparison of 3rd Story Displacements for NS Component of the El Centro
Ground Motion
172
Chapter 7.
Summary, Conclusions and Recommendations
7.1 Summary
Chapter 1 provides a brief introduction and outlines the objectives of the research
performed in this thesis. Chapter 2 discusses background information on the use of
supplemental damping devices to improve structural response and the types of dampers
used in this study. Dampers included are elastomeric dampers, viscous fluid dampers and
magneto rheological (MR) dampers. The use of a simplified design procedure for
designing structures with dampers is included. Finally, Chapter 2 concludes by discussing
the development of a prototype structure designED using the simplified design procedure.
Chapter 3 presents the design of the test structure. It begins by discussing the scaling of
the protype structure and selection of structural members by Dong (2012). It then covers
the development of details for the MRF test structure to avoid column damage during
testing. The design of continuity plates, doubler plates and welds is presented.
Chapter 4 describes the fabrication of the MRF test structure and the experimental test
setup of the DBF and MRF. An external bracing frame designed by Herrera (2005) is
used to provide out of plane bracing for both frames. Loading systems for each frame as
well as fixtures reacting the forces are described in this chapter.
Chapter 5 describes the instrumentation plan for the test structure. Sensors including
LVDTs, linear potentiometers, temposonics, accelerometers, simple strain gauges, full
173
bridges and load cells used to measure deformations and internal forces are described.
The derivation of calibration factors to determine axial force and moment from full
bridges is presented. Statics is provided for the calculation of internal forces not found
from direct measurement. A method for determining external friction force is also
presented. This chapter concludes with the calibration of the bay link fixture.
Chapter 6 describes the characterization of the DBF and development of the stiffness
matrix. An assessment of external friction in the test setup was performed and showed
that there is very little friction present in the test setup for the DBF. The assessment of
force-deformation behavior of various components of the test structure and fixtures is
conducted. This data will be used in future research to update finite element models of
the structural system. The development of a procedure for developing a stiffness matrix
based on the results of static test data and the use of a flexibility approach is shown. This
matrix is then used as the basis for numerical simulations and is compared to hybrid
simulation results.
7.2 Conclusions
The following conclusions were drawn from the work reported in this thesis:
1. Large-scale MRF and DBF test structures could be fabricated and erected in
laboratory.
2. T-connections needed modifying to reduce nonlinearities.
3. Rigid links could be successfully used in place of dampers to gather initial
characterization data for the calibration of numerical models of the DBF.
174
4. The use of load cells, full bridge load cells and displacement transducers allowed
global and local force-deformation responses to be obtained.
5. Friction force in test setup could be analyzed through the use of full bridge load
cells and frictional forces were determined to be low.
6. Development of a static stiffness matrix for use in hybrid simulations showed that
large scale steel test structure can have its stiffness accurately assessed through
static testing and the use of a flexibility approach.
7.3 Recommendations
The following recommendations are made for future work.
1. Perform characterization testing of the MRF to determine its elastic stiffness by
either detaching the DBF at its load attachment point to the loading beams or by
making use of the full bridges in the loading beams to determine the applied
forces in the MRF.
2. Preform coupon tests on drops of DBF and MRF structural members to
determine material properties. The most critical sections to test of the MRF are
the beams and columns as well as the DBF structural T sections.
3. Develop and improve the OpenSEES models of the test structure to improve
correlation between the model and the test structure.
4. Validate the simplified design procedure (SDP) by comparing the response of the
structure from the SDP with results of nonlinear time history analysis and by
showing the performance objectives of the SDP are met.
175
5. Comparisons should be made between the results from numerical and hybrid
simulations using the two possible testing configurations of the test structure
with dampers, (i.e., between hybrid testing using physical dampers, a physical
test structure and analytical mass; hybrid simulation using physical dampers,
analytic substructure of the test structure and analytical mass) to the determine
the cost-benefit relationship for each testing configuration and the necessity for
future frame tests in this area.
6. During testing the frame stiffness should be reassessed periodically to monitor
changes due to yielding of frame components.
7. An evaluation of the friction in the test setup when the MRF is attached to the
loading beams.
176
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179
Appendix
MRF Weld Inspection Report
180
VITA
Ryan James Ahn, the son of Timothy and Sandra Ahn was born on July 10, 1987 in
Dover, Delaware. In May 2010 Ryan earned a Bachelor of Science in Civil Engineering
from the Pennsylvania State University at University Park, Pennsylvania. Ryan began his
graduate studies in the Department of Civil and Environmental Engineering in Bethlehem
Pennsylvania in August of 2010. He will receive a Master of Science in Structural
Engineering in 2012n
181
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