cyclic loading performance of special truss moment frame with

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.