Forensic Analysis of Link Fractures in Eccentrically Braced Frames during the February 2011 Christchurch Earthquake: Testing and Simulation
Publication: Journal of Structural Engineering
Volume 141, Issue 5
Abstract
The earthquake on February 22, 2011, in Christchurch, New Zealand, resulted in the first documented field fractures of links in eccentrically braced frames (EBFs). A comprehensive forensic analysis of these fractures, which occurred in the parking garage of the Christchurch Hospital, is presented. The analysis is based on mechanical and spectrochemical testing and three-dimensional (3D) scanning of procured physical samples of the fractured links. The analysis features nonlinear time history simulations to characterize deformation demands and continuum finite-element simulations to determine the capacities based on a sophisticated fracture mechanics model. The exercise represents a multiscale end-to-end simulation of the system and provides insight regarding the observed fractures. The analysis reveals the inherent challenges in determining the proximate cause of the fractures because the fractures occurred because of a confluence of several interacting factors, primarily the intensity of shaking (several times the intensity that was expected during a design-level event) and the frame geometry, which severely amplified the imposed demands. In addition, the fractured links also suffered from an erection (fit-up) error, in which the link stiffener was not located (as specified) directly above the brace flange, producing a severe strain concentration. This flaw significantly reduced the deformation capacity; however, the simulation of hypothetical scenarios indicates that, even with this flaw, the links would (with high likelihood) have survived a design-level event. Strategies for mitigation include stricter tolerances for stiffener location, consideration of frame geometry to reduce amplification of rotation, and enhancement of the seismic hazard used for design. The limitations of the study are outlined.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The research described in this paper was funded by the National Science Foundation, Grant # CMMI 1138634. The results and opinions presented in this paper are solely of the authors and do not represent those of the Foundation. The authors are also grateful to the Canterbury District Health Board and Chris Allington of Holmes Consulting in New Zealand for consenting to provide the frame samples and Russell Berkowitz of Forell Elsesser Engineers in San Francisco, California, for providing photographs.
References
ABAQUS 6.12 [Computer software]. Providence, RI, Simulia.
AISC. (2010). “Seismic provisions for structural steel buildings.” ANSI/AISC 341-10, Chicago.
Armstrong, P. J., and Frederick, C. O. (1966). A mathematical representation of the multiaxial bauschinger effect, Berkeley Nuclear Laboratories, Research and Development Dept., Berkeley, U.K.
ASCE. (2007). Seismic rehabilitation of existing buildings, Reston, VA.
ASTM. (2011a). “Standard specification for structural steel shapes.” ASTM A992, West Conshohocken, PA.
ASTM. (2011b). “Standard test methods for tension testing of metallic materials.” ASTM E-8, West Conshohocken, PA.
Bruneau, M., Anagnostopoulou, M., MacRae, G., Clifton, C., and Fussell, A. (2010). “Preliminary report on steel building damage from the Darfield earthquake of September 4, 2010.” Bull. New Zealand Soc. Earthquake Eng., 43(4), 351–359.
Clifton, C., Bruneau, M., MacRae, G., Leon, R., and Fussell, A., (2011). “Steel structures damage from the Christchurch earthquake of February 22, 2011, NZST.” Bull. New Zealand Soc. Earthquake Eng., 44(4), 297–318.
Cubrinovski, M., et al. (2011). “Soil liquefaction effects in the central business district during the February 2011 Christchurch earthquake.” Seismol. Res. Lett., 82(6), 893–904.
Dusicka, P., Itani, A. M., and Buckle, I. G. (2010). “Cyclic behavior of shear links of various grades of plate steel.” J. Struct. Eng., 370–378.
Earthquake Engineering Research Institute (EERI). (2010). “The Mw 7.1 Darfield (Canterbury), New Zealand earthquake of September 4, 2010.” EERI Special Earthquake Rep., El Cerrito, CA.
Earthquake Engineering Research Institute (EERI). (2011). “Learning from Earthquakes: The M 6.3 Christchurch, New Zealand, Earthquake of February 22, 2011,” EERI Special Earthquake Rep., El Cerrito, CA.
Fell, B. V., Kanvinde, A. M., and Deierlein, G. G., (2010). “Large scale testing and simulation of earthquake induced ultra low cycle fatigue in bracing members subjected to cyclic inelastic buckling.” TR-172, John A. Blume Earthquake Engineering Center, Stanford Univ., Stanford, CA.
Galambos, T. V. (1998). Guide to stability design criteria for metal structures, 5th ed., John Wiley and Sons, Hoboken, NJ.
Kanvinde, A. M. (2004). “Micromechanical simulation of earthquake induced fracture in steel structures.”, John A. Blume Earthquake Engineering Center, Stanford Univ., CA.
Kanvinde, A. M., and Deierlein, G. G. (2006). “The void growth model and the stress modified critical strain model to predict ductile fracture in structural steels.” J. Struct. Eng., 1907–1918.
Kanvinde, A. M., and Deierlein, G. G. (2007). “A cyclic void growth model to assess ductile fracture in structural steels due to ultra low cycle fatigue.” J. Eng. Mech., 701–712.
Kanvinde, A. M., Fell, B. V., Gomez, I. R., and Roberts, M. (2008). “Predicting fracture in structural fillet welds using traditional and micromechanics-based models.” Eng. Struct., 30(11), 3325–3335.
Kasai, K., and Popov, E. (1986). “General behavior of WF steel shear link beams.” J. Struct. Eng., 362–382.
Kiran, R., and Khandelwal, K. (2014). “Experimental studies and models for ductile fracture in ASTM A992 steels at high triaxiality.” J. Struct. Eng.,, 140(2), 04013044.
Liao, F., Wang, W., and Chen, Y., (2012). “Parameter calibrations and application of micromechanical fracture models of structural steels.” Struct. Eng. Mech. Int. J., 42(2), 153–174.
Malley, J., and Popov, E. (1984). “Shear links in eccentrically braced frames.” J. Struct. Eng., 2275–2295.
McKenna, F., Fenves, G. L., Scott, M. H., and Jeremic, B. (2000). Open system for earthquake engineering simulation (OpenSEES), Pacific Earthquake Engineering Research Center, Univ. of California, Berkeley, CA.
Melchers, R. E. (1992). “Rotational stiffness of shallow footings.” Comput. Geotech., 13(1), 21–35.
Myers, A. T., Kanvinde, A. M., and Deierlein, G. G. (2009). “Testing and probabilistic simulation of ductile fracture initiation in structural steel components and weldments.” TR-170, John A. Blume Earthquake Engineering Center, Stanford Univ., Stanford, CA.
Myers, A. T., Kanvinde, A. M., and Deierlein, G. G. (2010). “Calibration of the stress modified critical strain (SMCS) criterion for ductile fracture in steels: Specimen size dependence and parameter assessment.” J. Eng. Mech., 1401–1410.
Okazaki, T., Engelhardt, M., Nakashima, M., and Suita, K. (2006). “Experimental performance of link-to-column connections in eccentrically braced frames.” J. Struct. Eng., 1201–1211.
Popov, E. P., and Engelhardt, M. D. (1988). “Seismic eccentrically braced frames.” J. Constr. Steel Res., 10, 321–354.
Popov, E. P., and Roeder, C. W. (1978). “Design of eccentrically braced frames.” Eng. J., Am. Inst. Steel Constr., 15(3), 78–81.
Prinz, G. S., and Nussbaumer, A. (2012). “On the low-cycle fatigue capacity of unanchored steel liquid storage tank shell-to-base connections.” Bull. Earthquake Eng., 10(6), 1943–1958.
Ramadan, T., and Ghobarah, A. (1995). “Analytical Model for Shear-Link Behavior.” J. Struct. Eng., 121(11), 1574–1580.
Rice, J. R., and Tracey, D. M. (1969). “On the ductile enlargement of voids in triaxial stress fields.” J. Mech. Phys. Solids, 17(3), 201–217.
Richards, P., Okazaki, T., Engelhardt, M., and Uang, C.-M. (2007). “Impact of recent research findings on eccentrically braced frame design.” Eng. J., Am. Inst. Steel Constr., 44(1), 41–53.
Richards, P. W., and Uang, C.-M. (2006). “Testing protocol for short links in eccentrically braced frames.” J. Struct. Eng., 1183–1191.
Ricles, J., and Popov, E. (1994). “Inelastic link element for EBF seismic analysis.” J. Struct. Eng., 120(2), 441–463.
Scott, B., Park, R., and Priestley, M. N. (1982). “Stress-strain behavior of concrete confined by overlapping hoops at low and high strain rates.” J. Am. Concr. Inst., 79(1), 13–27.
Standards New Zealand. (1997). “Steel structures standard incorporating Amendment No. 1:2001 and Amendment No. 2:2007.” NZS 3404, Wellington, New Zealand.
Standards New Zealand. (2010). “Structural steel—Hot-rolled bars and sections.” AS/NZS 3679, Wellington, New Zealand.
Stevenson, J. R., Kachali, H., Whitman, Z., Seville, E., Vargo, J., and Wilson, T. (2011). “Preliminary observations of the impacts the 22 February Christchurch earthquake had on organisations and the economy: A report from the field (22 February—22 March 2011).” Bull. New Zealand Soc. Earthquake Eng., 44(2), 65–76.
Tetko, I. V., Livingstone, D. J., and Luik, A. I. (1995). “Comparison of overfitting and overtraining.” J. Chem. Inf. Comput. Sci., 35(5), 826–833.
Trifunac, M. D., and Todorovska, M. I. (1998). “Nonlinear soil response as a natural passive isolation mechanism—The 1994 Northridge, California, earthquake.” Soil Dyn. Earthquake Eng., 17(1), 41–51.
Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 141 • Issue 5 • May 2015
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Apr 5, 2013
Accepted: Feb 4, 2014
Published online: Jul 23, 2014
Discussion open until: Dec 23, 2014
Published in print: May 1, 2015
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.