高強度プレストレストコンクリート杭とフーチング接合部の回転拘束度および破壊耐力に関する実験的研究

抄録

This paper discusses experimental results of full-scale bending-shear tests for pile-footing joint under various axial load conditions, in order to investigate degree of restraint for rotation at joint and ultimate strength of piles. As test specimens, 29 sets in total of prestressed high strength concrete (PHC) piles are used by combining three grades of effective prestress (σ_e=40, 80, 100 kg/cm^2) and two kinds of diameter (35cm, 50cm). Three types of joint method are selected in phase 1 test series. Type X is the most common method that pile cut together with PC bars is buried simply in footing with 10cm depth, and plain concrete is filled inside up to the length corresponding to pile diameter. Type Y is the same method as type X except that reinforced concrete is filled inside with a little longer length. Type Z is the method that pile cut leaving PC bars 50 times as long as those diameter is buried in footing with 10cm depth, and covered by steel pipe with concrete outside and filled with plain concrete inside to 40cm long from pile top. Similar three types of joint method, i.e., X', Y' and Z' are selected in phase 2 test series, in order to investigate effects of embedding length of pile head in footing. Statically indeterminate loading system is used, i.e., concentrated load is applied at intermediate point between pile head joint and the other pinned supporting point of pile, in order to produce simulated bending moment distribution of pile in the ground by horizontal load. Conclusions derived from experimental results are classified into the following two categories : 1) Degree of restraint for rotation at pile head joint α_r in the range of allowable capacity design is affected significantly by embedding length and axial load. When the ratio of embedding length to pile diameter changes from 0.2 to 1.0, α_r increases from 0.7 to 0.9, and from 0.4 to 0.75 in average, under the conditions with and without axial load, respectively. 2) Final state of PHC pile results in shear failure type, especially in axial load condition, so that it's important to make an effort to keep its ductility in ultimate capacity design.