Civil Engineering Association

Evaluation Of The Orientation Of 90° And 180° Reinforcing Bar Hooks

This report describes test results of a study initiated to evaluate the potential influence of hook tilt angle of standard reinforcing hooks on the bond strength of concrete. The topic of the evaluation of the orientation of 90 and 180 degree reinforcing bar hooks in concrete members was identified by the Concrete Reinforcing Steel Institute (CRSI) as high-priority for the reinforcing steel industry. In the test program conducted, a series of single bar and multiple bar specimens was designed and tested to examine bar behavior and potential group effects that may exist in wide flexural members with multiple bars, such as a slab or footing. Using beamend specimens, 90 and 180 degree standard reinforcing hooks were placed at varying angles to compare the angle of tilt and to compare the two hook types. Twelve single bar specimens and twelve multiple bar specimens, each containing either No. 5 or No. 8 standard reinforcing bars,were tested by axially loading the reinforcing bar(s) in tension. Measuring the bar displacement and strain at varying locations along the bar, load-displacement curves obtained were utilized in the analysis of hook tilt. Based on the results, design recommendations for tilted hooked bar anchorages were made. For No. 5 bars and smaller with concrete compressive strength, f’c, greater than 4500 psi, spacing between 0.5 and 2 times the hook length, A, and concrete cover equal to or exceeding the values used in this study, tilting reinforcing hooked bars from vertical at any angle did not compromise the structural integrity. For No. 5 bars and smaller with concrete compressive strength less than 4500 psi, spacing less than 0.5 times the hook length,A, or concrete cover less than the values used in this study, further study is needed. Additionally, further study is needed for bars larger than No. 5.