Steel wire prestress analysis of large section jacking prestressed concrete cylinder pipe (JPCCP): Site experiment and numerical investigation

As one of the key factors of Jacking Prestressed Concrete Cylinder Pipe (JPCCP), stress condition of the steel wire has a significant influence on the safety and durability of the JPCCP. In this paper, the stress of the steel wire was analyzed in the process based on the in-situ test monitoring results and numerical investigation in the water conveyance project in Shanghai. According to test results, the stress losses during the entire process were ruled out and turned out to be quantized. The reduction rate of steel wire was quite high in the early stage of prestress, and gradually slowed down with the time. The relaxation of steel wire was the main influencing factor of prestress loss. The numerical model of JPCCP was established and verified by field test data. Mechanical properties and failure modes of JPCCP under high inner water pressure and under different prestress losses were analyzed. After the initial prestress of steel wire was reduced from 1048 MPa to 888 MPa, the prestress of concrete in pipe core was reduced by 15%, while the compressive stress of the outer concrete was reduced by 23%. The water pressure carrying capacity of the structure was reduced by 10%. The larger the prestress loss of the steel wire was, the earlier the concrete in the pipe core entered the plastic phase. The results indicate that the prestress loss of steel wire has a direct and prominent influence on the bearing capacity of the water pressure on JPCCP. To help tunnel designers incorporate the prestress requirement into their basis of design and structural analysis, an assessment method was also proposed.