日本建築学会構造系論文集
Online ISSN : 1881-8153
Print ISSN : 1340-4202
ISSN-L : 1340-4202
機械式定着具を梁主筋に用いた外柱基礎梁接合部における梁主筋の定着長さと柱のせん断補強筋比の影響
大西 直毅西村 康志郎山口 悠太
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ジャーナル フリー

2018 年 83 巻 743 号 p. 167-177

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 Mechanical anchorage has recently been used for simplifying the arrangement of reinforcement in beam-column joint. In AIJ Standard for Structural Calculation of Reinforced Concrete Structures (published in 2010), there are examples of application of mechanical anchorage for foundation beams, and also mentioned that the exterior foundation beam-column joint with pile should be regarded as equivalent to T-shaped joint.
 Yield hinge is generally set not at the ends of foundation beams but at column bases to obtain a global yield mechanism. In considering the use of mechanical anchorage at the ends of a foundation beam, it is possible that the resistance of the anchorage is influenced by the failure of the column base.
 In this paper, loading test of exterior foundation beam-column joint is reported to consider the performance of anchorages at maximum strength and to observe the state of deterioration. Test variables were development length of beam bars, and shear reinforcement ratio of column. In addition, we assumed a model to evaluate the maximum strength of negative loading (see Fig. 2) and compared the calculated value with the experimental value. The following conclusions were drawn from the results:
 (1) The specimen PJ1L with the development length 0.8D (D = column depth) did not satisfy the required development length calculated with yield stress of beam bars. However, if it is calculated with the existing stress of beam bars, it satisfied the development length, though the other two specimens did not satisfy the required development length with both calculation method. In the relationship between lateral force of beam and drift angle, the strength of PJ1L was gradually increased up to the drift angle of 2.0 % after yielding of main column bars. It seems that whether the specimen satisfies the required development length with existing stress of beam bars made the difference of the strength and ductility performance.
 (2) The maximum strengths of the specimens PJ2S and PJ3SR with the development length 0.5D were 0.85 or 0.89 times lower than the flexural strength of column. Because the strain at column bars remained on the same level after yielding, and because V-shaped crack extended from the end of beam bars became wider, it seems that the damage around the anchorage of tensile beam bars was more severe than PJ1L.
 (3) The specimen PJ3SR, which has a greater transverse reinforcement than the specimen PJ2S in the column base and the upper part of the joint, suppressed the widening of cracks along the compressed reinforcing bars of column during positive loading (see Fig. 2) and the soundness of the cover concrete was preserved. It seemed that this made the maximum strength to be higher than that of PJ2S, and the strength increased up to the drift angle of 2.0% even after yielding of main column bars. PJ3SR also had higher yield strength in negative loading. However, damage around the fixing part became large leading to the ultimate state in the end. In the comparison of the equivalent viscous damping factor, PJ3SR with larger shear reinforcement ratio of column was higher than PJ2S at 2.0 % drift angle.
 (4) The ultimate strengths of PJ1L calculated in accordance with the capacity evaluation model in negative loading were close to the experimental value. The model in the ultimate state overestimated the maximum strength of the other two specimens, but the calculated strength at the column bars yield can estimate the maximum strength in the tolerance of six percent. This formula expresses the lower strength with shorter development length, and also the higher strength with higher shear reinforcement ratio of column.

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