Seismic Performance of Embedded Column Base Connections Subjected to Axial and Lateral Loads
Publication: Journal of Structural Engineering
Volume 143, Issue 5
Abstract
Embedded column base (ECB) connections are used in mid- to high-rise steel moment frames to transfer base moments and forces into the footing. These connections, which feature a steel column embedded into a concrete footing, are used when exposed base plate connections are unfeasible for providing the requisite strength or stiffness. Results from five full-scale tests on ECB connections are presented to examine their seismic response. The test specimens, representing prevalent construction practice, were subjected to cyclic lateral deformations in the presence of an axial (tensile or compressive) load. Test variables included embedment depth, axial load, and column size. Damage was observed in the form of concrete crushing in the bearing zones ahead of the column flanges, shear cracking in the joint panel region, and flexural cracking of the entire footing. Two types of failure were observed: (1) gradual loss of strength due to concrete crushing ahead of the flange and (2) upward pryout of concrete on the tension side of the connection. The former mode was dominant in the specimens with deeper (762 mm) embedments, whereas the latter was dominant in shallower (508 mm) embedments. These failure modes and experimental measurements suggest that the base moment is resisted through a combination of horizontal bearing stresses on the column flanges and vertical bearing stresses on the embedded base plate. All specimens sustained significant deformations (2–7% column drift) prior to load loss or failure. It is determined that even if designed as rotationally fixed, the specimens have significant flexibility, which must be considered in simulation and design. Limitations of the study are discussed, and suggestions are provided for the development of a strength model based on the experimental findings.
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Acknowledgments
The authors are grateful to the Charles Pankow Foundation and the American Institute of Steel Construction for providing major funding for this project. Supplementary funding was provided by graduate fellowships at the University of California, Davis. Gregory Deierlein of Stanford University provided valuable feedback, as did Geoff Bomba of Forell Elsesser Engineers, Paul Cordova of Simpson Gumpertz and Heger, and Ron Klemencic and Rob Chmielowski of Magnusson Klemencic Associates.
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Information
Published In
Journal of Structural Engineering
Volume 143 • Issue 5 • May 2017
Copyright
©2017 American Society of Civil Engineers.
History
Received: May 13, 2015
Accepted: Nov 2, 2016
Published online: Jan 30, 2017
Published in print: May 1, 2017
Discussion open until: Jun 30, 2017
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