Experimental study on mechanical properties of prestressed concrete cylinder pipes (PCCPs) under external load

Prestressed concrete cylinder pipes (PCCPs) have been applied for various water conveyance projects recently, especially in long distance. PCCPs not only bear internal water pressures, but also external loads. The excess of external loads may cause major accidents. However, the mechanical behavior of PCCPs under external load is different from that of PCCPs under internal pressure. In this study, a three-edge bearing test (TEBT) of a PCCP was performed to study its mechanical properties under external load. Meanwhile, the fiber Bragg grating (FBG) sensing technology and pulse pre-pump Brillouin optical time-domain analysis (PPP-BOTDA) optical fiber sensing technology were successfully employed to monitor the deformation of PCCPs. The test results show that the deformation of five components of the pipe is proportional to the external load. At the springline of the pipe, the outer concrete core and the prestressing wire are in tension, the inner concrete core and the steel cylinder are in compression. The loading status at the crown and invert of the pipe are opposite with those at the springline of the pipe, but the deformation coordination is consistent. Moreover, the test results demonstrate that PPP-BOTDA-based distributed optical fiber sensors can not only accurately monitor the real-time loading response of the PCCP under the external load like FBG point optical fiber sensors, but also obtain the dynamic and continuous strain distribution of the circumferential section of the pipe. This study has identified the relationship of the external load and deformation, the interaction and strain distribution of each component of PCCPs. This study also confirms that the distributed optical fiber sensing technology can provide an effective means for the structural health monitoring in long-term operation of PCCPs.