Wataru Koyanagi

FRACTURE MECHANICS APPROACH TO EVALUATION OF FLEXURAL STRENGTH OF CONCRETE

Size effects and shape effects on the flexural strength of concrete were examined through experiments and numerical analysis with fracture mechanics concepts. Based on the numerical results, the authors proposed an equation for estimating the flexural strength of concrete beams with square or circular cross sections. The beam depth, tensile strength, and the characteristic length of concrete beams are the parameters in the proposed equation. The estimated values of flexural strength given by the equation are in good agreement with the experimental results, especially for square beams. The equation gives moderate values for the flexural strengths of various kinds of concrete, including normal concrete, high-strength concrete, lightweight concrete, mortar, and polyester resin concrete.

Studies on Tensile Stress and Crack Growth of Steam Cured Prestressed Concrete Members.

Longitudinal cracks are found occasionally in the anchorage zone of pretensioned prestressed concrete members with small covering depth. We made an assumption that the crack growth at the time of prestressing was resulted from the flaw in concrete which took place close to the prestressing tendon because of the temperature difference between the tendon and the concrete during steam curing at an early setting period of the concrete. Experimental and analytical studies were made on the effect of temperature difference on the crack growth in hardened concrete and the results approved the above assumption.

STUDY ON THE CEMENT GROUT MATERIALS FOR STRENGTHENING OF CONCRETE SLABS

橋梁・床版の老朽化や車両大型化に伴う補強方法として, 樹脂系接着材を用いた鋼板接着工法が用いられてきた. しかし, より良い施工性・経済性を望んだ場合, セメント系充填材の採用が考えられる. 本研究では, セメント系充填材の材料特性 (特に付着力) や施工性に着目し検討・評価を加えた. この結果, 実用性に富んだ材料を選定するとともに, セメント系充填材に必要とされる要求性能を明らかにすることができた.

Failure Behavior and Structural Design of Concrete Members Reinforced with Continuous Fiber Reinforcing Materials

Continuous fiber reinforcing materials (CFRM), which are made of continuous fibers such as aramid, carbon, etc., bound with resin, are expected to be substituted for steel bars in reinforced and prestressed concrete structures. CFRM are free from corrosion but brittle and the Young’s modulus is low as compared with steel bars. In this paper, the features of CFRM are outlined, and then the ductile and/or brittle failure behavior are investigated using 3-element “parallel” and “series” systems. The favorable failure modes are discussed with relation to the members with CFRM.

FAILURE BEHAVIOR AND DESIGN METHOD OF REINFORCED AND PRESTRESSED CONCRETE BEAMS HAVING HIGH STRENGTH AND HIGH TOUGHNESS

ABSTRACT The purposes of this study are to establish the structural toughness design procedure of reinforced concrete (RC) and prestressed concrete (PC) beams through an energy method and to develop high performance RC and PC beams having high ultimate strength and high toughness. RC and PC beams with different amount of reinforcing and prestressing bars were loaded up to the complete failure. Plain concrete and steel fiber reinforced concrete were adopted. The degree of the ductile failure behavior of RC and PC beams could be roughly controlled by the proposed ductility index λ, which is defined by the sectional constants and the material properties.

Toughness Evaluation and Its Application to Concrete Structural Design

The evaluation, improvement and application of concrete toughness are discussed. It is shown that the differential signal between factored load and displacement is effective to control unstable failure of concrete specimens at loading tests. The relations among impact load, displacement, kinetic energies and duration of concrete beams subjected to impact are presented. Concrete having both high toughness and high strength can be produced by adding steel fibers at high percentage into high strength cement concrete or polyester resin concrete. The analytical relation between the compressive toughness of concrete and the toughess of RC (reinforced concrete) beams in bending is derived. The ductility index is proposed and its validity is proved by experiments of PC (prestressed concrete) beams.