Experimental Performance of Block-Out Connections at the Base of Steel Moment Frames
Publication: Journal of Structural Engineering
Volume 145, Issue 7
Abstract
In a block-out connection, a steel column is connected to a footing through an opening (block-out) in a slab-on-grade that is later filled with unreinforced concrete. In design, engineers generally neglect any beneficial effects of the block-out concrete. The objective of this study is to experimentally quantify the effect of block-out concrete on the lower-bound flexural strength and stiffness of block-out connections at the base of steel moment frames. Eight specimens were tested with varying column shape, block-out depth, and baseplate/anchor rod designs. The block-out concrete increased the connection flexural strengths by 69%–91% for block-out depths that were 1.2–1.5 times the column depth. A strength model proposed in previous work was found to reasonably predict the flexural strength, accounting for the effects of block-out concrete. With regard to stiffness, specimens with block-out concrete depths at least 1.15 times the column depth could be accurately modeled as fixed at the top-of-footing elevation.
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Acknowledgments
Funding for this research was provided by the American Institute of Steel Construction; Mr. Tom Schlafly was the project manager and coordinated a professional advisory group that provided input on the experiment designs. Laboratory personnel at Brigham Young University provided essential assistance in conducting the experiments. The authors appreciate the contributions of others but retain responsibility for the work and conclusions.
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Published In
Journal of Structural Engineering
Volume 145 • Issue 7 • July 2019
Copyright
©2019 American Society of Civil Engineers.
History
Received: Dec 5, 2017
Accepted: Nov 14, 2018
Published online: Apr 29, 2019
Published in print: Jul 1, 2019
Discussion open until: Sep 29, 2019
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