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Title |
Lap Splice Test of SD400 D10 Reinforcing Bars Confined with Spiral or U-Bar
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Authors |
김진규(Jin-Gyu Kim) ; 천성철(Sung-Chul Chun) ; 김인호(In-Ho Kim) |
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DOI |
https://doi.org/10.4334/JKCI.2021.33.4.389 |
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Keywords |
나선철근; U철근; 겹침이음; 설계식 spiral; U-bar; lap splice; design equation |
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Abstract |
Splices of reinforcing bars are needed to connect old and new concrete slabs. For lapping bars, breaking concrete in the old slab cannot be avoided, and this may cause deterioration in the old slab and increase repair costs. Connections are designed to be located in low stress regions and, SD400 D10 bars are often used. In this study, lap splice tests on SD400 D10 confined by spiral or U-bar were conducted. Test variables included concrete strength, lap length, spacing of splices, location of splice, existence of confining bars, and types of confining bars and a total of 34 specimens were tested. Most specimens showed higher bar stresses than expected. Splices of SD400 D10 confined by spiral or U-bar with only 10 db lap length developed a design yield strength of 400 MPa. Developed bar stresses were calculated through sectional analyses. Twenty-six stresses, including two specimens from the ACI 408 database, which had similar conditions to this study, were compared with four equations. The comparison shows that the ACI 408 equation can predict the bar stresses of confined SD400 D10 splice because, among the four equations, an average of test-to- prediction ratios by the ACI 408 equation is 1.12 and is the closest to 1.0, and the COV of the ratios is 12 % and is the lowest. More variables are included in the ACI 408 equation than the others and the ACI 408 equation can accurately predict the bar stresses of confined SD400 D10 splice. A design equation of splice length of SD400 D10 confined by spiral or U-bar is proposed from the ACI 408 equation incorporating a 5 % fractile coefficient.
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