Researchers confirm U-bolts’ role in to rebar cage safety

Nevada-Reno investigators observed the behavior of 43-ft. cages fabricated with U-bolt or tie wire cross-bar connections. U-bolts can add lateral integrity, they conclude, and help lower the rate of cage incidents resulting in injuries or fatalities and construction schedule delays.

A Charles Pankow Foundation investigation geared to identifying fabrication and assembly practices curtailing rebar cage collapse or failure incidents confirms the potential of U-bolt hardware to replace tie wires commonly used in lateral and transverse bar connections and increase lateral strength. The Haymarket, Va. organization teamed with the American Society of Civil Engineers Construction Institute, University of Nevada, Reno and a host of heavy/civil construction interests to prove the U-bolts’ efficacy in tests and engineering analyses. They have released their findings and perspectives in “Application of U-bolt Connector for Improving the Safety of Rebar Cages” and “Guidelines for Circular Rebar Cage Assembly with U-bolt Connectors,” both posted at

Along with reviewing analytical models, Nevada-Reno Department of Civil & Environmental Engineering investigators measured U-bolt connections’ mechanical behavior through experiments determining force-deformation response behavior in different degrees of freedom and for different rebar conditions. Data obtained from a previous study on a full-scale tie-wired rebar cage was used to develop and calibrate a nonlinear finite element model of the test specimen. The force-deformation response of U-bolt connections was then included in the model, replacing the tie wires, to investigate the effect of mechanical connectors on the lateral stiffness and strength of the rebar cage.

Joining Pankow Foundation and the ASCE Construction Institute in research funding were Association of Drilled Shaft Contractors, Association of Foundation Drilling, Concrete Reinforcing Steel Institute, Harris Rebar and Nucor Corp., Keller Companies, Kiewit Corp., Parsons Corp., P.J.’s Rebar, Siefert Associates LLC, and Williams Form Engineering. 

Nucor Corp. is scouting the Pacific Northwest to build a rebar micro mill with annual capacity of 650,000 tons, a full range of product sizes, and spooling capabilities for smaller bar. The facility would become the company’s fourth such operation, its template especially tailored to concrete reinforcements and lower cost production than larger steel facilities covering a broader range of end uses. A Pacific Northwest mill would serve external accounts, plus Nucor’s Harris Supply rebar distribution, fabrication and installation business. 

“We have had great success with our rebar micro mills in Florida and Missouri and are on schedule to begin operating our third micro mill in the first quarter of 2025, which we are currently building in North Carolina,” says Nucor Chair Leon Topalian. “Locating a new rebar micro mill in the Pacific Northwest provides us with an excellent opportunity to better serve our customers in the region and continue to build our modern economy with some of the most sustainable steel in the world.”