異形鉄筋のコンクリート内の定着性状に及ぼす拘束の効果に関する実験的研究

Abstract

Vertical wall reinforcing bars of a boxed wall precast concrete structure in Japan must be anchored straight in the foundation beam. Sometimes, the beam width may not be sufficient to develop anchorage strength in the concrete although the AIJ (Architectural Institute of Japan) Standard for Structural Calculation of Reinforced Concrete Structure requires minimum concrete volume for the development of deformed bars. A series of pull-out tests were carried out to investigate structural performance of anchored bars using various prototype specimens. The purpose of the test series was to study the effect of various parameters and to clarify the failure mechanism. A new series of tests were carried out using high strength deformed bars and varying the foundation beam widths. The anchored bars were pulled out from the base beam exhibiting the relationship between maximum bond stresses and flexural stresses with in the beam. It can be concluded as follows: (1) D19 (diameter 19 mm) deformed bars of Grade SD345 and SD685 (nominal yield stress of 345 and 685 MPa) can be anchored with a development length of 40d (d: bar diameter) for the precast reinforced concrete box-wall construction. When deformed bars are anchored using sheath pipes after construction of the beam, the sufficient development strength was achieved. (2) D19 deformed bars of Grade SD980 were pulled out of the beams of 180, 220, 330, and 440mm widths. (3) Bond failure of a deformed bar developed from the beam top and progresses to deeper region with load. (4) Flexural compressive stresses in the foundation beam increased bond resistance of the deformed bars. (5) Flexural tensile stress or strain of concrete in the foundation beam had less influence on the bond resistance along a deformed bar. (6) The beam width had not much effect on the development strength of a deformed bar within the foundation beam. (7) The development strength of deformed bars was proportional to the flexural compressive stresses in the foundation beam. (8) The development strength increased at a higher rate for beam width less than 180mm, but the increase rate became smaller for the beam width more for 220mm to 440mm.