Research and application of a new method for axial force test of prestressed high-strength concrete pipe piles

In order to figure out actual shaft resistance, axial forces of pile shaft have to be calculated based on strain test, which is a challenge for heat and steam cured prestressed high-strength concrete pipe piles. Disadvantages of three common methods of strain test and the empirical linear equation between axial force and strain are analyzed. A new strain test method, namely the slot-forming wood method, is proposed and applied in laboratory and field test. Taking pipe pile PHC500AB-125 as an example, laboratory tests were performed to establish the nonlinear function between axial force and strain. Field tests were performed and strains were tested by the slot-forming wood method. Results calculated by the nonlinear function between axial force and strain were compared with that by traditional linear equation to reveal the difference. The tests indicated that the new method of strain test was applicable and useful since the survival rate of strain gauges was high and the accuracy has been improved. Overcoming the disadvantages of the traditional linear equation, the proposed function between axial force and strain is more accurate. The study provides theoretical basis for technology innovation in pile test and for revision of related technical standards.