Local Buckling Behavior of Round Steel Tubes Subjected to Compressive Loads

Joseph Moore, Benjamin Fell1(PI) 1Department of Civil Engineering, California State University, Sacramento

Experimental Design Results/Acknowledgements

Background Information: • In general, for pipes fitting into the range of D/t ratios used in the field,

30 – 100, compressive loading is not enough to cause fracture in the pipe (Sreekanta 2001).

• Compressive loading tends to cause bifurcation in several areas along the pipe followed by several lobes, usually 2 – 3. As compressive force is continued to be monotonically increased on the specimen one of the lobes becomes more pronounced while the others smooth out (Bardi 2001).

• Tests on unpressurised specimens determined for D/t ratios ranging from 20 -60 that buckling could be induced from ~95 – 110 Ksi (Paquette 2006).

References: BAO, Xiaoyi, and CHEN, Liang. “Recent progress in optical fiber sensors based on brillouin scattering at University of Ottawa.” Photonic Sensors 1.2 (2011): 102 – 117. Bardi, F. C. and Kyriakides, S. “Plastic Buckling of circular tubes under axial compression Part 1: Experiments & Part 2: Analysis” International Journal of Mechanical Sciences 48 (2006): 830 – 854. Das, Sreekanta, et al. "Wrinkle behavior under cyclic strain reversal in NPS12 pipe." 20th International Conference on Offshore Mechanics and Arctic Engineering. 2001. Gresnigt, A. M., and R. J. Van Foeken. "Local buckling of UOE and seamless steel pipes." Proc. Eleventh International Offshore and Polar Engineering Conference (ISOPE), Stavanger. 2001. Hutchinson, John W. Advances in Applied Mathematics: Plastic Buckling. New York: Academic Press Inc., 1974. Article. Mahdavi, Hiva, et al. "Significance Of Geotechnical Loads On Local Buckling Response Of Buried Pipelines With Respect To Conventional Practice." Canadian Geotechnical Journal 50.1 (2013): 68-80. Academic Search Premier. Web. 17 June 2014. Mohareb, M., Kulak, G.L., Elwi, A., and Murray, D.W. “Testing and analysis of steel pipe segments.” Journal of Transportation Engineering 127 (2001): 408 – 417. Murray, David W. "Local buckling, strain localization, wrinkling and postbuckling response of line pipe." Engineering Structures 19.5 (1997): 360-371. Paquett, J. A. and Kyriakides, S. “Plastic buckling of tubes under axial compression and inernal pressure” International Journal of Mechanical Sciences 48.8 (2006) 855 – 867. Ravet, Fabien, et al. "Distributed Brillouin Sensor For Structural Health Monitoring." Canadian Journal Of Civil Engineering 34.3 (2007): 291-297. Academic Search Premier. Web. 17 June 2014. Sheinman, I. and Simitses, G. J. “Buckling and postbuckling of imperfect cylindrical shells under axial compression” Computers and Structures 17.2 (1983): 277 – 285. Sohal, I. and Chen, W. “Local Buckling and Sectional Behavior of Fabricated Tubes” Journal of Structural Engineering 113.3 (1987) 519 – 533. Teng, J. G. and Hu, Y. M. “Behavior of FRP – jacketed circular steel tubes and cylindrical shells under axial compression” Construction and Building Materials 21 (2007): 827 – 838.

Objectives:

Determine how much force is required to reach each pipe’s critical strain capacity and compare it to the predicted force derived from the empirical equations of past studies. Determine how the D/t ratio affects the amount of force required to

reach each pipe’s critical strain capacity. Determine how the length of the pipe affects the amount of force

required to reach each pipe’s critical strain capacity. Determine if a pipe can reach a point of fracture prior to cyclic loading. Inform a physics-based fracture model utilizing stress and plastic strain

demands from finite element analyses

1) Capabilities:

Empirical Equations Used From Literary Findings:

O.D.

max-thickness

(Fmax = 50 kip) D/t

max-thickness

(Fmax = 250 kip) D/t

4 0.051 79 0.093 43

6 0.057 105 0.102 59

8 0.063 128 0.110 73

10 0.068 147 0.117 86

12 0.073 164 0.123 97

14 0.078 179 0.129 108

16 0.083 192 0.135 118

18 0.088 205 0.141 128

20 0.092 216 0.146 137

22 0.097 226 0.152 145

24 0.102 236 0.157 153

2) Maximum Capacity Candidates

O.D. Length Wall Thickness D/t

4” 8”

.083” – Sch 5 48 4” 12”

4” 24”

6” 8”

.083” – GA 14 72 6” 12”

6” 24”

12” 8”

.109” – GA 12 110 12” 12”

12” 24”

3) Nominal Pipe Sizes

Specimen

300 Kip

Screw Jack

Introduction This project will investigate the local buckling induced fracture behavior of round steel tubes subjected to axial compressive loads, representative of observed failures in buried pipelines during seismic events. The investigation will be planned and conducted in the Sacramento State structural engineering laboratory, investigating compressive wrinkling fracture behavior across a range of pipe lengths and diameter-to-thickness (D/t) ratios of the pipe cross-sections. Ancillary tensile coupon tests will be extracted from the steel pipes to obtain fundamental material properties. The experimental results will be used to inform a physics-based fracture model utilizing stress and plastic strain demands from finite element analyses.

55 Kip Actuator

Load Cell

12.0000

Specimen

The initial step in designing the experiment in this study was to determine what pipe specimens we would be able to test with the given equipment that we have. Using the principle that the maximum force divided by the buckling capacity must be equal to the area of cross section, we were able to determine test candidates.

Pipe Testing • 6 specimens were taken from 10 feet long A135B steel pipes and welded

onto ½” end plates. The specimens were loaded into the 300 kip screw jack and compressed to an average axial strain of 4.2%.

This material is based upon work supported by the Chevron Corporation, Howard Hughes Medical Institute, the National Marine Sanctuary Foundation, National Science Foundation, S.D. Bechtel, Jr. Foundation and the California State University Sacramento Office of Research Affairs. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the funders. The STAR program is administered by the Cal Poly Center for Excellence in STEM Education (CESAME) on behalf of the California State University.

Ancillary Testing

7" X 7" X 12 " PLATE

(QTY: 6)

CL

CL

2.25"

2.25"

Ø0.625" (Typ.)

Base metal

Specimen sY (ksi) eY (%) sUTS (ksi) eF (%)

OD 4-1 52.657 0.476 57.350 15.345 32.246 OD 4-2 56.730 0.376 61.901 22.863 60.770 OD 4-3 60.428 0.396 64.174 19.888 50.235 OD 4 - AVG 56.605 0.416 61.142 19.365 47.750 OD 4 - Median 56.730 0.376 61.901 19.888 60.770 OD 4 - COV 6.867 12.687 5.683 19.551 30.206 OD 6-1 56.626 0.389 70.305 20.575 52.906 OD 6-2 60.580 0.409 74.683 23.687 57.900 OD 6-3 58.153 0.468 72.643 21.398 45.771 OD 6 - AVG 58.453 0.422 72.544 21.887 52.192 OD 6 - Median 58.153 0.409 72.643 21.398 52.904

OD 6 - COV 3.411 9.676 3.020 7.368 11.680 OD 12-1 62.805 0.453 75.331 20.136 44.450 OD 12-2 61.382 0.389 75.459 23.786 61.194 OD 12-3 63.640 0.416 76.722 20.191 48.548 OD 12 - AVG 62.609 0.419 75.837 21.371 51.397 OD 12 - Median 62.805 0.416 75.459 20.191 48.548 OD 12 - COV 1.824 7.700 1.014 9.787 16.981

Weld metal

Pipe Testing

4) Experimentation

Ancillary testing • 14 Coupons were taken from the specimens to determine mechanical

properties of materials based on ASTM E8/8M – 09. Hardness was also determined using the Rockwell scale.

0

10

20

30

40

50

0 0.1 0.2 0.3 0.4

Stre

ss (

kip

s)

Displacement (in)

OD 4 - 8

Future Work: This research is the introduction to a much larger project which will continue on at the Sacramento State structural engineering laboratory. Further studies will include compressive testing of 15 additional specimens and following these tests, all 21 specimens will be cyclic tested for fracture strength.

Special thanks to Jim Ster & Mike Newton from the CSUS Machine Shop

OD Wall

Thickness D/t Length

Fmax

(kips) scr (kips) εcr

4 .078” 51

8” 46.3 46 0.00332125 12” 38.5 30 0.00200325

Average 42.4 38 0.00266225 COV 13.0081 29.77 35.00673256

6 .078” 77

8” 58.25 31 0.003375875 12” ** ** 0.005195833

Average - - 0.004285854 COV - - 30.02680047

12 .098” 122

8” 128.75 80 0.0047275 12” 161.5 160 0.0066425

Average 145.125 120 0.005685 COV 15.9571 47.14 23.81898832

**The data for this section was not collected in the same manner as the other tests and was omitted.

0

0.002

0.004

0.006

0.008

0.01

0.012

0 50 100 150 200

Cri

tica

l Str

ain

D/t

Test Data (L=8")

Test Data (L=12")

2.42(t/D)^1.59

0.5(t/D) - 0.0025

15(t/D)^2