Alternative TitleAFRPシートで曲げ補強したRC梁の耐衝撃挙動に関する実験的研究
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近年，RC構造物の耐衝撃性向上法の１つとして，高強度重量比や高耐食性および高施工性を有するFRP材料を用いた補強方法に着目した実験的検討が行われている。しかしながら，FRP材料を用いたRC構造物の合理的な耐衝撃設計法に関しては，未だ確立されていないのが現状である。このような観点より，本研究では，衝撃荷重を受けるFRP材料で補強したRC構造物の合理的な耐衝撃設計法手法を確立することを目的に，アラミド繊維（AFRP）シートで曲げ補強したRC梁を対象に静荷重および重錘落下衝撃荷重載荷実験を実施した。ここでは，シート補強量がRC梁の耐衝撃性に与える影響を確認するために補強量を３種類に変化させた。測定項目は，衝撃荷重，支点反力，載荷点変位，シートの軸方向ひずみに関する時刻歴波形および実験終了後のRC梁のひび割れ分布である。本論文の構成は以下の通りである。第１章は本論文の序論であり，本研究の背景や既往の研究，および目的について述べている。第２章では，既往の研究をレビューするとともに，FRP材料を用いた補強方法について述べている。第３章では，本研究で対象とした試験体や静荷重および重錘落下衝撃荷重載荷実験法の概要について述べている。第４章では，無補強及びシート補強梁を対象とした静荷重載荷実験について述べている。実験結果より，シート補強量が大きいほど最大荷重は増加すること，およびシート補強RC梁の破壊形式は既往の研究成果と同様に，シート補強量によって“曲げ圧壊型”と“剥離破壊型”に分類されることなどを明らかにしている。第５章では，無補強およびシート補強RC梁を対象に単一衝撃荷重載荷実験について述べている。実験結果より，衝撃荷重を受けるシート補強梁は，無補強梁と比較して最大載荷点変位を35%程度抑制できること，シート補強の有無にかかわらずRC梁の最大/残留変位は，入力衝撃エネルギーに対してほぼ線形に増加する傾向を示すこと，衝撃荷重を受けるシート補強RC梁の破壊モードは，シートの補強量によって“シート破断型”と“シート剥離型”の２種類に分類されること，さらに前者は静荷重下における“曲げ圧破型”に，後者は“剥離破壊型”に対応することなどを明らかにしている。第６章では，漸増繰り返し載荷実験について述べている。その結果，絶対最大変位と累積入力エネルギーには線形関係が成立すること，漸増繰り返し載荷における破壊形式は単一衝撃荷重時と同一の傾向を示すことなどを明らかにしている。第７章は本論文の結論であり，本研究で得られた知見を整理している。
Traditional methods of strengthening or retrofitting existing concrete structures, such as steel plate bonding, section expansion, and external post-tensioning, have been used. However, these techniques have the disadvantages of increasing the structure's weight, being difficult to install, and having the reinforcing material corrode, resulting in higher maintenance expenses. Fiber-reinforced polymer (FRP) materials have many outstanding advantages, including corrosion resistance, a high strength-to-weight ratio, and ease of installation. Due to these features, many studies and applications on FRP materials containing carbon, glass, aramid, and basalt fibers have been carried out in civil engineering. Most of the FRP materials were applied to strengthen RC beams in flexure and/or shear under static loadings. Design recommendations for reinforcing concrete structures with externally bonded FRP systems have been developed and are being widely applied. However, worldwide terrorist activities and threats have recently posed a significant challenge to civil infrastructure, necessitating the construction of structures with blast and impact resistance. As a result, FRP materials can be used to strengthen RC constructions against both static and blast and impact loads. However, studies on FRP-strengthened RC beams against impact loading are relatively limited. Design specifications for strengthening RC members under impact loading have not been established yet. From this point of view, this work focuses on RC beams with stirrups that approach the ultimate state statically and demonstrate flexural failures. Low-velocity drop-weight impact loading tests on RC beams strengthened in flexure with Aramid FRP sheets were performed with varying drop heights of the weight (0.5, 1.0, 2.0, 2.5, 3.0, and 3.5m) and sheet volume (415, 830, and 1660 g/m2) to investigate the strengthening effect and the failure mode of the RC beams. The experiments in the case of consecutive impact loading with gradually increasing energy were also conducted to investigate the impact-resistant characteristics of the RC beams. Here, the sheet volumes used were 415, 830, and 1660 g/m2. The drop height of the weight was increased in the order of 1, 2, 2.5, and 3 m up to the corresponding ultimate state of the beam. Furthermore, to study the load-carrying capacity, strain distribution, crack distribution, and failure behavior of the beams, static loading experiments were also tested on the RC beams. The results were compared with impact loading tests, calculated results by means of the multilayered method, and the failure mode of the previous study. From the experimental results, the following are the findings of this research: (1) In the case of the static loading, the failure mode of the strengthened RC beams with AFRP sheets was classified into two types: flexural compression failure and debonding failure, depending on the sheet volume. These results are in good agreement with the previous study. (2) In the case of impact loading (with a single loading method), the maximum and residual displacement of the strengthened beams can be restrained by up to 35% and 85%, respectively, compared with unreinforced beams. (3) The maximum/residual displacement of the RC beams with/without AFRP sheets linearly increased with the input impact energy. (4) The failure mode of the strengthened RC beams under impact loading was classified into two types depending on the sheet volume: rupturing and debonding. The former corresponds to the flexural compression failure mode, while the latter corresponds to the debonding failure mode under static loading. (5) In the case of the consecutive drop-weight impact loading, the absolute maximum/residual deflections of the strengthened beams were linearly distributed corresponding to the accumulated input impact energy, and the failure mode of RC beams in this case had the same tendency as in the case of the single impact loading.
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2023-03-02T11:18:11+09:00
Data Provider (Database)国立国会図書館 : 国立国会図書館デジタルコレクション