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The University of Texas, Arlington
Shih-Ho (Simon) Chao, Ph.D., P.E.Sanputt Simasathien, Ph.D. Candidate
Chatchai Jiansinlapadamrong, Ph.D. Candidate
Hokkaido UniversityTaichiro Okazaki, Ph.D.
CYCLIC LOADING PERFORMANCE OF SPECIAL TRUSS MOMENT FRAME WITH DOUBLE-CHANNEL CHORD MEMBERS
110NCEE
Special Truss Moment Frame (STMF)
2
Photo courtesy of John Hooper San Jose Airport, CA
Benefits of STMFHigher elastic stiffness than moment frames;Higher structural redundancy (multiple energy-
dissipating mechanisms); Truss girders can be economically used over
longer spans;Open-webs can easily accommodate mechanical
and electrical ductwork.
3
Design of Members outside Special Segment Based on “Expected Shear Strength, Vne” at the middle of the Special Segments (S.S.)
4
neV
1F
2F
3F
4F
Plastic Hinges
1F
2F
3F
4F
Plastic Hinges
neV
2sL 2sL
Special Segment Special Segment
2010 AISC Seismic Provisions (based on Chao and Goel, 2008):
5
Contribution from X‐shaped diagonals
Rotational demands of plastic hinges in the chord members are much larger than that of flexural members in moment frames
6
Story Drift Ratio (%) Plastic Rotation (rad.)
0.50 0.000.75 0.011.00 0.021.25 0.031.50 0.041.75 0.052.00 0.062.25 0.072.50 0.082.75 0.093.00 0.10
For a typical STMF with the ratio of truss girder span to the length of special segment = 3.75:
The relation between the story drift ratio and plastic hinge rotation of the chord members can be approximately estimated from the following equation:
Other Limitations in the AISC Seismic Provisions
7
Story Drift Ratio (%) Plastic Rotational Demand of Chord Member (rad.)
1.00 0.0352.00 0.0853.00 0.135
For typical STMFs with one Vierendeel panel at S.S. – truss girder height = 4-ft; span length = 30-ft L/Ls = 30/(1.5x4) = 5.0
DOUBLE-CHANNEL COMPONENT TEST
8
Rotational capacity of the double-channel sections is controlled by three major instabilities: lateral-torsional buckling (LTB), flange local buckling (FLB), and web local buckling (WLB). They can occur simultaneously and strongly interact with each other.
LTB in Double‐Channel SectionFLB/WLB in Double‐Channel Section
9
AISC Seismic Provisions do not allow any attachment located within the plastic hinge region. Therefore LTB may still occur at the plastic hinge even the lateral supports are placed at the end of the plastic hinge.
10
2010 AISC SeismicProvisions:
Lateral supports
Potential PH region
Typical STMF (photo courtesy of John Hooper)
118
1
Cross Section
22.5 23
Weld-FreeLength
2C8x18.75
6
9
13/16
7/16 9
7/16 9
Proposed double-channel connection with direct lateral support at plastic hinge
A 1-in. central gusset was used to provide direct lateral support at the plastic hinge without violate the AISC requirement
Horizontal stitches are used to maintain built up sectionConventional
stitches failed
12
Overall View of the Component Test Setup at The University of Texas at Arlington
Comparison of Component Test Specimen SP 13 (2C8x18.75) to the Full-Scale STMF 1-1 Specimen
12"x3"x3" Stitch (with corner cut)
1"x3"x3" Stitch (TYP.)
4'-1112" 4'-111
2"
2'-412"
1'-8
"1'
-8"
1'-512"
1'-5" 1112"
9"2"
1'-11" 1'-11"1112"
1" TYP.
2'-1" 2'-1"1'-11" 1'-11"
6" 2'-1" 1'-11"
1'-8
" Loading Point
Vertical members are not butted up to the chord members
14
SP13: experiment results
-10 -8 -6 -4 -2 0 2 4 6 8 10Member Rotation (%)
-3000
-2500
-2000
-1500
-1000
-500
0
500
1000
1500
2000
2500
3000-2 0 2
Prototype Structure Story Drift (%)-1.5 0 1.5-1 0 1-0.5 0 0.5-2.5 0 2.5-2.74 0 2.74
-0.8Mp = -0.8FyZ = -1,112
0.8Mp = 0.8FyZ = 1,112
End of Test
Without special detailing, the specimen sustained high member rotation and story drift of 9.11% and 2.74% respectively
No lateral torsional buckling
Comparison of Component Test Specimen SP 12 (2C6x13) to the Intermediate Vertical Members of Full-Scale STMF 1-2
6"
5"1'
-2"
Loading Point
Note: The real setup was rotated 90 degree CCW
1'-2
"
1'-8
" 6"
5"
16
SP12: experiment results
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12Member Rotation (%)
-1400
-1200
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
1200
1400-2 0 2
Prototype Structure Story Drift (%)-1.5 0 1.5-1 0 1-0.5 0 0.5
-0.8Mp = -0.8FyZ = -583
0.8Mp = 0.8FyZ = 583
End of Test
Asymmetry of displacement due to reach of maximum tension capacity of the actuator. Reached 1.5% story drift (6.25% member rotation) in one direction and 2% story drift (10.6% member rotation) in the other direction.
1. Verify the 2010 AISC Vne equation (Chao and Goel, 2008);
2. Check if the aspect ratio of S.S. could be extended to about 2.5 (this will reduce the rotational demands at the chord members). The current limits are between 0.67 and 1.5;
3. Investigate the possibility of relaxing the stitch spacing in the S.S. (from 14 in. to 23 in.);
4. Investigate the possibility of relaxing splicing location of chord members;
5. Check the performance of STMF up to up to 3~4%(demand under MCE ground motion) drift ratio;
6. STMF with multiple Vierendeel panels at the S.S.
Objectives
FULL-SCALE STMF TESTS
18
Test Setup and STMF Specimen at NSF NEES MAST lab
A
A
D
D
B2
B2
C2
C2B1
B1
C1
1"x3"x3" Stitch (TYP.)
6'-6
"4'
-0"
6'-11332" 4'-10" 9'-11" 4'-10" 6'-113
32"
2332"
4'-712"
28'-10"
4'-1112" 4'-111
2"
17'-0
"
3'-2
"
2332"
4'-712"
2'-412"
1'-1"
1'-8
"1'
-8"
1'-512"
1'-8
"
3'-0"
10"
1'-5
"
7'-0
1 2"
1'-5" 1112"
1'-7" 1'-5"
1" T
YP.
1'-7
"9"
2'-0"5"
2'-11"
2"
2"
27'-1316"
4'-3"
4'-4"2'-11
2 "
2'-2"
1'-0"
3'-7
1 8"3'
-0"
5'-1
1 2"4'
-0"
1'-3
38"
1'-11" 1'-11"
1" 1"
1'-6"
2'-2"
1'-11"
1112"
1" TYP.
1" T
YP.
STRONG FLOORSTRONG FLOOR
2'-1" 2'-1"1'-11"
C1
31'-91316"
Load Transfer BeamW18x106
W30x261
28'-6"
W30x261
6'-6
34"
2'-7
1 4"4"
178"
1'-11"
HSS8x4x12 HSS8x4x1
2
STMF Test Specimen 1 (STMF 1.1): 2-C8x18.75 chords
2-C8x18.752-C6x13
Aspect Ratio of Special Segment = 2.5
STMF Test Specimen 1 (STMF 1.1): Special Features
Stitch spacing greater than required by AISC 341-10.
Weld-free zone.
Extended “weld-free” gusset plateto provide lateral support at plastic hinge zone.
No “butt-up” connection.
Special stitches extend PH
region.
Diagonal web to be field welded.
3'-4
"
3'-4
"10"
1'-7
"
10"
1'-7
"
18'-9"
9'-11"
1'-6"
6"
1'-8
" 9"
1112"
1" TYP.
2'-3" 1'-8" 1'-8" 2'-4"
2'-11"
1'-5" 1112"
1'-8
"3'
-4"
3'-312" 1'-8" 1'-8" 3'-31
2"
1112"
1'-5"
1'-6"
6"
1'-8
"9"
1112"
2'-11"
1'-8
"
3'-4
"
3'-5" 3'-5"
1" T
YP
.10"
1'-7
"
10"
1'-7
"
STMF Test Specimen 1 – Cut locations for Specimen 2 (STMF 1.2) splice
Cut locations
Air arc gouge
Diagonal web to be field welded.
STRONG FLOORSTRONG FLOOR
2'-10"
3'-10"
2'-10"
3'-10"
2'-1"
1'-1"
2'-1"
1'-1"
6'-6
"4'
-0"
6'-11332" 4'-10" 9'-11" 4'-10" 6'-113
32"
2332"
4'-712"
28'-10"
4'-1112" 4'-111
2"
17'-0
"
3'-2
"
2332"
4'-712"
2'-412"
1'-1"
1'-8
"1'
-8"
1'-512"
1'-8
"
3'-0"
10"
1'-5
"
7'-0
1 2"
1'-5" 1112"
1'-7" 1'-5"
1" T
YP.
1'-7
"9"
2'-0"5"
2'-11"
2"
2"
27'-1316"
4'-3"
4'-4"2'-1 1
2 "
2'-2"
1'-0"
3'-7
1 8"3'
-0"
5'-1
1 2"4'
-0"
1'-3
38"
1'-8" 1'-8"
1" 1"
1'-6"
2'-2"
1'-11"
1112"
1" TYP.
1" T
YP.
STRONG FLOORSTRONG FLOOR
10" 10"
1'-7
"
1'-7
"1'
-7"
10"10"
31'-91316"
28'-6"
6'-6
34"
2'-7
1 4"4"
178"
10"
STMF Test Specimen 2 (STMF 1.2): 2-C8x18.75 chords with two intermediate vertical members
2-C8x18.752-C8x18.75 + 2-1”x10” SP
2-C6x13
2-C6x13
Aspect Ratio = 2.5
Splice Location
Splice Location
STMF Test Specimen 2 (STMF 1.2): Special Features
Splice locations within one-half the panel length from
the end of the SS.
Multiple Vierendeel panels in the SS.
Web cutout with butt-up weld.
Web stiffeners in chord members.
Stitch spacing greater than required by
AISC 341-10.
Weld-free zone.
Extended “weld-free” gusset plateto provide lateral support at plastic hinge zone.
No “butt-up” connection.
STMF Specimen Loading Protocol
STMF 1.1
STMF 1.1 @ -2% DriftSTMF 1.1 @ -1% Drift
STMF 1.1 @ -4% DriftSTMF 1.1 @ -3% Drift
STMF 1.2
STMF 1.2 @ -2% DriftSTMF 1.2 @ -1% Drift
STMF 1.2 @ -4% DriftSTMF 1.2 @ -3% Drift
STMF 1-1
27
No LTB
Complete Tear of Chord Member
Members Outside SS Remain Elastic
Hysteretic Behavior
Preliminary Conclusions
Full-scale STMF specimens with double-channel section members showed ductile and stable response under large displacement reversals.
Several seismic detailing in the current AISC Seismic Provisions can be safely relaxed such as the aspect ratio of S.S. to 2.5; greater stitch spacing (50%greater) in the S.S., and allowing splicing of chord members within one-half the panel length from the ends of the S.S.
The proposed special detailing using extended gusset plates at the corner of S.S. with weld-free zone effectively provides direct lateral support to the PH zone and increases the ductility of STMFs.
Preliminary Conclusions
Intermediate vertical members increase both stiffness and strength of STMFs. They are designed to be the first elements that dissipate the majority of the earthquake energy, and can be easily replaced when they are damaged in a moderate earthquake event.
AcknowledgementThe authors wish to thank the following organizations andpeople for their contribution and support throughout the project:
- National Science Foundation (NSF), George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES)
- American Institute of Steel Construction (AISC)- Dr. Carol Shield, Paul Bergson, Rachel Gaulke, Lauren
Snyder, Michael Boldischar, Christopher Bruhn, Samantha Thomas and staff at the University of Minnesota’s Multi-Axial Subassemblage Testing (MAST) Laboratory
- Dr. Subhash Goel, the University of Michigan- John Hooper, Magnusson Klemencic Associates- Falcon Steel Company- Structural Solutions Inc.