Nobuaki Takagi

Retrofiting Method of RC Beams Using Tensioned Carbon Fiber Sheets

Retrofitting methods for RC beams were proposed in the present work. Tensioned carbon fiber sheets were employed to improve the bending strength of the RC beams for both live and dead loads. A novel tensioning device was developed to apply the tensile stress to the carbon fiber sheets and to prevent the interfacial debonding between the carbon fiber sheets and RC beam. Experimental results showed that the proposed device could apply by far higher tensile stress to the carbon fiber sheets than the conventional methods. As a result, the bending strength of the beams retrofitted by the present method was higher than that of the beams retrofitted by the conventional methods. Especially, the critical load at the crack initiation in the concrete increased about 3.8 times comparing with that of the original RC beam and about 1.6 times comparing with that of the RC beams retrofitted by the conventional methods by using the present method.

DEVELOPMENT OF PC TRUSS BEAMS WITH CYLINDRICAL CONTINUOUS FIBER REINFORCEMENT DIAGONAL

本研究では, 筒状連続繊維補強材を型枠および拘束体として用い, 膨張材の混入によりケミカルプレストレスを導入した高強度コンクリート部材の製作方法およびトラスなどの構造部材に適用するための基本的特性について実験的に検討を行った. また, 本部材を斜材に適用したPCトラス桁の静的載荷試験を行い, せん断耐力および変形性状などについて検討を行った.その結果, 筒状連続繊維補強材を用いたモルタル部材は, トラス部材として十分機能することが確認できた. 引張斜材破断後もPCトラス桁は, 耐荷機構が圧縮斜材と床版部材によるタイドアーチ機構に移行し, じん性的な破壊性状を示した.

Study on Shrinkage Characteristics of High-Strength Silica Fume Concrete

Autogenous shrinkage and drying shrinkage tests were carried out to determine the shrinkage characteristics of high-strength concrete. Three levels of water-cementitious materials ratios [W/C+SF): 20, 30 and 50%] were chosen. The drying shrinkage test with specimens of 10x10x40 cm under the condition of 20 + or - 1 degree C and 60 + or - 5%RH started at the age of 7 days or 28 days after the measurement of autogenous shrinkage. The autogenous shrinkage strain was also measured in other specimens until the age of about two years. The autogenous shrinkage strain increased both in its amount and its percentage in the total shrinkage strain with the decrease of W/(C+SF). Almost the same total shrinkage strain was observed after about one year in the specimens under the drying condition, independent of the mixture proportions of concrete, the curing method or its period.