STRUCTURAL PERFORMANCE OF IMPROVED SIMPLIFIED CONNECTION SYSTEM AT PRECAST CONCRETE PILE HEAD UNDER HIGH AXIAL LOAD

An improved semi-rigid connection system which is used to connect a pile head and a pile cap has been proposed by authors and it has proved to be effective to reduce bending moment of a pile head under general level of axial load. However, in recent years, high bearing capacity piles, which have more than twice capacity of general piles, have become widely used. To investigate performances of the proposed system under such a high axial load, full-scale structural tests are conducted. From the test results, it is revealed that the maximum bending moment at a pile head (Mmax) almost agrees with a maximum eccentric moment (Me) under low axial stress, but Mmax/Me decreases with axial stress increase. This paper proposes an experimental formula to evaluate Mmax using Me and axial stress ratio (σn/σB, σn : axial stress at a pile head, σB : concrete strength of a pile cap) under the condition that a pile cap isn't damaged with strength decrease, and an analytical method to judge the condition of its application.