Side-Face Blowout Failure of Headed Bars in High-Strength Concrete
Hye-Jung Sim and Sung-Chul Chun
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The design provisions of ACI 318-19 for the development length of headed bars do not distinguish different failure modes and limit concrete compressive strength to 70 MPa (10 ksi). Failure types regarding headed bars terminating in an exterior beam-column joint can be classified into side-face blowout, concrete breakout, pullout, or joint shear failure. The anchorage capacity of headed bars depends on the failure mode. In this study, a side-face blowout strength of headed bars in high-strength concrete over 70 MPa(10 ksi) was investigated. Thirty-two simulated exterior beamcolumn joints were tested using 80 and 120 MPa (11.6 and 17.4 ksi) concrete of design compressive strength. Side-face blowout failure was anticipated by preventing the other failure modes. Two descriptive equations were developed based on the test results including previous studies. One is expressed as the summation of two terms representing the contributions of head bearing and bond, while the other is xpressed as a single term of total anchorage strength, similar to the design equation of ACI 318-19. Using the two proposed equations, the design yield strength of headed bars against side-face blowout failure can be safely developed in highstrength concrete up to 120 MPa (17.4 ksi).