Junichiro Niwa

Experimental Study on the Possibility of Using Steel Fiber–Reinforced Concrete to Reduce Conventional Rebars in Beam-Column Joints

AbstractIn rigid-framed railway bridges, because of excessive amounts of rebar in beams and columns, overcongestion at the beam-column joints of rigid-framed railway bridges was investigated in this paper. The experiments were conducted on eight one-sixth scaled specimens that include four T-joint and four knee-joint specimens. In the control specimens, the amount of steel rebars and their arrangements and detailings resembled the as-built configuration of the rigid-framed railway bridge in Japan. In the other specimens, the amount of steel rebars was reduced and steel fibers were varied as 0, 1.0, and 1.5% by volume. The experimental results of the specimens were compared in terms of crack patterns, load-displacement relationships, ductility, energy dissipation capacity, and stiffness degradation and found that the performance of the control specimens and specimens with 1.5% of steel fibers and reduced steel rebars was comparable.

Effect of Post Shear Reinforcing Methods with Plate and Head Anchored Shear Reinforcing Bars

Some reinforced concrete (RC) structures in Japan which were built before 1980’s had low shear reinforcement and actually failed in shear. Accordingly, various shear strengthening methods, such as steel jacketing, FRP sheet jacketing, have been applied for existing RC structures. A new post shear reinforcing method with a plate and head anchored shear reinforcing bars (PHB method) has also been developed and widely used on site. In this study, some influential factors on this new method were experimentally investigated. A total of seven RC slender beams were tested under a four-point bending loading with the parameters of the spacing, the diameter and the embedded length of plate and head anchored shear reinforcing bars (PHBs). All beams had a rectangular cross section and a fixed a/d ratio of 3.2. The experimental results showed that PHB method improved the shear capacity of RC beams and the shear capacity of RC beams was affected by the spacing of PHBs, whether the PHBs were crossed by the diagonal crack or not. However, the magnitude of the shear capacity became smaller when the effective coefficient (β aw ) was reduced. With the increase in the spacing of PHBs, the shear capacity of RC beams decreased. This result suggests that the shear capacity can be controlled by increasing the shear reinforcement ratio. Furthermore, the shear reinforcement effect can be also promoted by shorter embedment length.

TESTING METHOD FOR RETAINED WATER OF FINE AGGREGATE BY UTILIZING CENTRIFUGAL FORCE

It was presumed that in reality fine aggregate would hold surface moisture peculiar to its own in addition to water defined by the JIS testing method for content of absorbed moisture of fine aggregate. The authors tried to clarify the actual conditions of the retained water by a new testing method by utilizing centrifugal force. As the results of a series of experimental studies, a fundamental conception of the testing method could be proposed. This testing method can measure the retained water as the sum of absorbed moisture and surface moisture of fine aggregate. Besides the conception, basic test results were presented.