Performance of Steel composite concrete pile with high toughness using an inner steel tube

Steel composite concrete pile was developed consisting of double steel tubes, with an inner steel tube installed on the inside face of concrete of an SC pile (hereafter referred to as "WSC pile") for enhancing deformation capacity. The inner steel tube restricts peel-off of concrete in the steel tube during crushing, which is an issue with the SC pile, and enhances the constraining effect of concrete thereby improving the deformation capacity of the WSC pile. This paper reports a series of bending shear tests performed to study the deformation capacity of WSC pile under high compressive load and axial tensile load. Bending shear tests were conducted in three series: "A series" tests for confirming the effect of double steel tubes; "B series" tests for validating the effect on the deformation capacity of WSC pile due to change in the axial force ratio; and "C series" tests to assess the restoring force model of WSC pipe considering the results of the A series and B series tests. Findings from the test results of the different series were as follows: (1) In the SC pile, bearing capacity dropped steeply and toughness reduced with the peeToff of concrete from the crushed internal surface. In the WSC pile using double steel tubes, the peel-off of internal surface of concrete was prevented and bearing capacity did not drop steeply after it reached the peak due to the effect of the inner steel tube. (2) In the range of axial force ratio of-0.31 to +0.32, the WSC pile had adequate deformation capacity with ductility factor exceeding 6.0 and also exceeding the limit of deformation angle of 1/50 radians. To ensure adequate deformation capacity, it was observed that inner steel tube with diameter to thickness ratio ti/ri ≧0.04 must be used to restrict the buckling advance in the said tube. (3) Assessment method using reliable bending moment rMu was proposed as the restoring force model of the WSC pile, and the validity of this model was confirmed. © 2019 Architectural Institute of Japan. All rights reserved.