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Mechanical Properties and Stress-Strain Model of Re-Bars Coldly Bent and Straightened (굽힌 후 편 철근의 기계적 성질과 응력-변형률 모델)

  • Chun, Sung-Chul;Tak, So-Young;Ha, Tae-Hun
    • Journal of the Korea Concrete Institute
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    • v.24 no.2
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    • pp.195-204
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    • 2012

  • In the construction of high-rise buildings, bent re-bars are manually straightened to connect slabs to core-walls, which are usually cast before floor structures. During cold bending and straightening of re-bars, plastic deformation causing work hardening, Bauschinger effect and aging hardening is unavoidable. Tensile tests of coldly bent and straightened re-bars were conducted with test parameters of grade, diameter, and bend radius of re-bars as well as age between bending and straightening. Test results showed that proportional limits were lower and strain hardening occurred without yield plateaus. Inside and outside of re-bars with compression and tension deformations, respectively, during bending showed lower yield points due to Bauschinger effect and no yield plateaus due to work hardening, respectively. When re-bar grade was higher, yield point became significantly lower where Grade 400 re-bars had yield strengths lower than specified yield strength of 400 MPa. Because the surface of re-bar has higher strength than the core of re-bar, Bauschinger effect was more obvious for higher-grade re-bars. When age between bending and straightening was greater, yield strength increased and elongation decreased (i.e. embrittlement occurs). Using measured data, stress-strain relationship for straightened re-bars was developed based on Ramberg-Osgood model, which can be used to evaluate stiffness of joints when straightened re-bars are applied.

  • https://doi.org/10.4334/JKCI.2012.24.2.195 인용 PDF KSCI