基礎梁主筋を機械式定着したSFRCパイルキャップの耐震性能

抄録

 In this study, the seismic performance of a steel fiber reinforced concrete (SFRC) pile cap using headed bars as main reinforcement in its foundation beams was examined by a lateral loading test and a non-linear 3-dimentional FEM analysis.

 In order to investigate the ultimate shear strength of the SFRC pile cap, a specimen designed to ensure a shear failure of its pile cap was prepared and tested under a lateral loading. The study showed that the critical region of the foundation beam would develop within the pile cap where shear cracks concentrated (area limited by the opposite sides of the column and pile faces).

 Whereas the first main shear crack formed along the diagonal line connecting the compressive parts at the opposite beam end sections, the other crack formed along the line connecting the compressive part at the foundation beam end section to the head anchors of the foundation beam longitudinal bars of the same beam end side.

 Also, in order to investigate the stress transfer mechanism of the pile cap when subjected to a lateral loading, a non-linear 3-dimensional FEM analysis was carried out, considering the Izumo model to define the tensile properties of SFRC. The analysis could accurately reproduce the experimental results, in terms of the shear force – story drift angle relationship, and stress – story drift angle relationship of the reinforcement.

 Also, a double strut model, involving the development of two struts in the pile cap, was identified as the stress transfer mechanism under lateral loading. The first strut to be formed connects the compressive parts at the opposite foundation beams end sections. The other strut to be formed connects the compressive part at the foundation bema end section to the head anchors of the foundation beam longitudinal bars of the same beam end side.

 An FEM analytical model, similar to the tested specimen, but with a square planar shape pile cap was also investigated. The analytical results showed that the deviation of the horizontal failure surface was about θ_h=60° from the headed bar axis. In addition, the ultimate shear strength of the pile cap sub-assemblage was determined by considering the lesser of the double strut model strength and the anchors pull-out strength when the horizontal failure surface is θ_h=60°.