コンクリート系梁の主筋座屈に基づく安全限界性能の定量化

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タイトル別名
  • QUANTIFICATION OF COLLAPSE PREVENTION PERFORMANCE OF CONCRETE BEAMS BASED ON LONGITUDINAL REBAR BUCKLING
  • コンクリート系梁の主筋座屈に基づく安全限界性能の定量化 : 靭性型コンクリート系建物の安全限界性能指標の提案
  • コンクリートケイリョウ ノ シュウスジザクツ ニ モトズク アンゼン ゲンカイ セイノウ ノ テイリョウカ : ジンセイガタ コンクリートケイ タテモノ ノ アンゼン ゲンカイ セイノウ シヒョウ ノ テイアン
  • －Proposal of collapse prevention performance index for ductile concrete buildings－
  • －靭性型コンクリート系建物の安全限界性能指標の提案－

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<p>1. Introduction</p><p>In the authors’ previous study3) on weak beam-strong column type RC moment-resisting frames (Figs. 1 and 2), buckling of longitudinal rebars was visually observed at the beam ends at large drift ratios (Fig. 4 and Photo 1). This result indicated that the buckling of beam longitudinal rebars was related to the safety limit (collapse preventaion performance) of weak beam-strong column type frames. However, to date, no method is presented to quantitatively evaluate the ultimate performance of RC frames at the buckling of beam longitudinal rebars. Hence, numerical and practical evaluation methods for the buckling of beam longitudinal rebars are proposed and verified through comparisons with the previous test3), as described above, and an additional one.</p><p>2. Experimental investigations</p><p>A prototype building of this study was introduced (Fig. 1), then the preceded tests of two moment-resisting frame specimens with/without RC secondary walls partially representing the prototype building were summarized (Figs. 2 to 4 and Photo 1). From the tests, buckling of the beam longitudinal rebars was visually observed after peeling off of the cover concrete at the ends of the beams (Photo 1). It indicated that the buckling of the beam longitudinal rebars affected the ultimate performance of the specimens.</p><p>3. Quantification of the safety limit (collapse prevention performance) of RC beams based on longitudinal rebar buckling</p><p>A numerical method to evaluate buckling occurrence of beam longitudinal rebars was proposed by comparing the stress-strain behavior of the beam longitudinal rebar with the buckling resistance by Eqs. 2 and 6. Thus, one of the specimens described in Chapter 2 was replaced by an idealized numerical model (Figs. 8 and 9) and numerically analyzed (Figs. 10 and 11). The analysis gave a good agreement for a drift at the beam longitudinal rebar buckling with that from the experiment (Fig. 13).</p><p>4. Simplification for application to practical design</p><p>Since the neutral axis on cross-sections of general RC beams is likely to be close to rebar under compression, the strain of the beam longitudinal rebars described in Chapter 3 was assumed to be zero under the maximum compression. This assumption simplifies the evaluation method proposed in the previous chapter and provides a practical evaluation method for the ultimate performance of RC beams at the buckling of beam longitudinal rebars by Eqs. 9 and 10. An estimated ultimate hinge rotation by the practical method was also verified to show a good agreement with the experimental result (Table 4).</p><p>5. Additional verification based on a full-scale RC beam test</p><p>An experimental study was performed using a full-scale beam specimen focusing on buckling of longitudinal rebars. This specimen also showed buckling behavior of the longitudinal rebars at the member end (Photo 2), then deteriorated (Fig. 23). The hinge rotation angle at the buckling of longitudinal rebars was evaluated as 1.26%rad based on the practical method proposed in Chapter 4. Consequently, the estimation was consistent to the experimental result (Table 8).</p><p>6. Conclusions</p><p>The present paper experimentally showed the safety limit (collapse prevention performance) for RC beams with buckling of longitudinal rebars; thus, proposed numerical and parctical evaluation methods. The proposed methods well evaluated the ultimate hinge rotations of the beam specimens at the longitudinal rebar buckling.</p>

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