Experimental study on the influence of scattered broken wires on the structural performance of prestressed concrete cylinder pipe

Abstract

Given that the prestressed concrete cylinder pipe (PCCP) derives compressive strength from high-tensile prestressing wires, breaking of steel wires is endangering the safety of PCCP lines. To deeply explore the influence of broken wires on the performance of PCCP, two 3.4 m PCCPs with the same design parameters are tested until failure by separately cutting their steel wires in clustered and scattered manners. And this paper mainly presents the destructive test with scattered broken wires (SBWs) under the water pressure of 1.15 MPa. To collect spatially continuous strain data, four different types of distributed optical fibers are applied on five material layers of the test pipes during the production. The results show that the distribution of breakpoints is highly scattered and each broken wire regains its full tension gradually over about a 60° angle from the breakpoint when the number (ratio) of SBWs does not exceed 120 (39.6 %). As a consequence of the subsequent wire breakage, the scattered breakpoints gradually concentrate, and then mortar cracking and delamination from the wires occurs and increases the length of the wire needed to regain full tension. The numbers (ratios) of SBWs corresponding to the onset of visible cracks in the outer concrete, and mortar, yielding of the steel cylinder, visible cracks in the inner concrete, and final failure are 125 (41.3 %), 145 (47.9 %), 165 (54.5 %), 170 (57.8 %), and 185 (61.1 %), respectively. The measured sizes of breakpoint separation show that the SBWs in one wire-cutting zone has small influence on other zones. And the number of SBWs is greater than three times that of clustered broken wires at the final failure. Both the number and concentration degree of broken wires should consequently be factored into the condition assessment of PCCP. It is worth reminding that the test results obtained are not to be applied indiscriminately to other pipe designs.