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  • 多段配筋RC梁のサイドスプリット型付着割裂耐力に関する考察
  • タダンハイキン RCリョウ ノ サイドスプリット カタツキチャクカツレツタイリョク ニ カンスル コウサツ

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 When a reinforced concrete flexural member is designed against shear loads according to the AIJ standard for reinforced concrete structures, bond performance between reinforcing bars and concrete should be verified. The bond splitting strength in the AIJ standard is based on pull-out test results of longitudinal deformed bars embedded in concrete. The bond strength is evaluated as shear stress on the surface of the bars. On pull-out test of deformed bars, bond strength of the deformed bar in second layer is apparently lower than that of the bar in first layer because of influence of bond stress in the first layer. In the AIJ standard, the bond strength in the second layer is simply reduced multiplying by 0.6. However, on bending-shear test results of R/C beams, when the deformed bar in second layer cut off, the bar performs higher strength. That is because bond stress distribution in the first and second layers is different from the case that all the double layered bars are arranged continuously through the span of beam. On the other hand, although more than three layers of longitudinal bars are arranged in foundation beams these days, the provision in the AIJ standard doesn't show methods for the bars more than three layers. It is necessary to consider the bond stress in all the tension bars totally in order to evaluate the side-splitting bond strength.<br><br> In this paper, evaluation method of the side-splitting bond strength is reviewed in order to examine bond performance of the R/C beams with multi-layered longitudinal bars including cut off bars.<br> The previous pull-out test results and bending-shear test results were reviewed in order to avoid side-splitting bond failure of the beams arranged more than three layers and including cut off bars. As a result of the revision, a new method for evaluating tensile force of all the longitudinal bars at the side-splitting bond failure is proposed. In this method, the direct shear failure of the concrete at the reinforcement layer is considered rather than the bond stress of each bar. The tensile force at the bond failure is expanded and simplified from the bond strength provided in the Design Guidelines for Earthquake Resistant Reinforced Concrete Buildings Based on Inelastic displacement Concept published by AIJ in 1999. However, the bond stress on the bar surface should be verified for local bond failure of the cut-off bar, corner-splitting failure, and V-notch splitting failure. If bond strength of cut-off bar in the second layer is estimated higher than the present provision, although it is the result observed in the loading test of the beam, a problem may occur. The problem can be avoided when the proposed method is adopted.<br> In order to examine the new method, the tensile force at the bond failure was applied to shear strength formula provided in the 1999 AIJ Guidelines. It is rational to avoid the side-splitting bond failure by examine the shear capacity of the beams. The 1999 AIJ guidelines provide Tx, which is the bond strength, in the shear strength formula. In this paper, the proposed method was applied to Tx. The modified shear strength formula is verified by comparing with the previous test results. The test results of the R/C beam specimens of single, double and more than three layers arrangement, and the specimens including cut off bar, were selected. As the results of comparison, the modified method shows good agreements with the test results with almost the same accuracy as the method in the 1999 AIJ guidelines.


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