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Title |
A Reevaluation of Anchorage Strength of Headed Bars in Exterior Beam-Column Joints
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Authors |
심혜정(Hye-Jung Sim) ; 천성철(Sung-Chul Chun) |
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DOI |
https://doi.org/10.4334/JKCI.2018.30.2.207 |
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Keywords |
외부 보-기둥 접합부 ; 확대머리철근 ; 정착강도 ; 측면파열파괴 ; 접합부 전단파괴 exterior beam-column joint ; headed bars ; anchorage strength ; side-face blowout failure ; joint shear failure |
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Abstract |
Failure modes of exterior beam-column joints, where headed bars as beam longitudinal bars are terminated, are classified into concrete breakout, pullout, side-face blowout, and joint shear failures. The design equation for the development length of headed bars of KCI (2012) is derived from lap splice tests and does not consider the characteristics of applied members and failure modes. For safe and economical design, the anchorage of headed bars should be designed considering each failure mode. This study reevaluates the anchorage strengths of headed bars in exterior beam-column joints of previous studies using the current design code and previous models. Pullout failure does not occur due to the existence of the head in headed bars and concrete breakout failure can be prevented by adjusting the effective depth of beam and anchorage length. For the side-face blowout failure, the current design code significantly underestimates the anchorage strength of headed bars and Chun et al. (2017)'s model including the effects of side cover and transverse reinforcement can properly evaluate the anchorage strengths of headed bars. For the joint shear failure, the design provisions of KCI (2012) on transverse reinforcement and joint shear strength can be applied. For the specimens satisfying the requirements for the transverse reinforcement, beam flexural failures with ductile behavior were observed or joint shear failures occurred with a shear strength ratio (Vj/Vn) of 1.0 or higher. Consequently, exterior beam-column joints where headed bars were anchored as beam longitudinal bars can be safely and economically designed if side-face blowout and joint shear failures are prevented.
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