Theoretical Research On Mechanical Behavior Of Prestressed Concrete Cylinder Pipe

Prestressed Concrete Cylinder Pipe(PCCP)is a kind of high quality composite pipe. In the field of large diameter pipes, it has been demonstrated more competitive than other pipes. The mechanical performance of PCCP is not uniform yet, because of its complicated structure and work condition. In this paper, the mechanical behavior of PCCP is researched, design method of prestressing is discussed, distributing rule of stress, cracking and peeling performance and anti-crack reliability of PCCP are also analyzed.First of all, the mechanical model is established in PCCP working stage, based on the elastic plane strain theory of axisymmetric multilayer cylinders and the mechanism of the ring-like strands action. Design method of prestressing is put forward according to the aim at the crack control and the ultimate bearing resistance, then the method is amended compared with the finite-element analysis.The distributing rule of the biggest ring-like stress in the condition of different burying depth , hydraulic pressure, thickness of pipe wall and rank of concrete, the developing of cracks and the coating delamination are analyzed by finite-element analysis. It is shown as follows: The ring-like stress of pipe wall increases with the increscent burying depth and hydraulic pressure. The biggest ring-like stress of pipe wall decrease obviously with the thickness of pipe wall rising, on the contrary, the variation of stress is not obvious with the rank of concrete rising. The mortar cracks prior at springline and the crack expands towards both sides along with increasing of the internal pressure. The outer core cracks at the springline earlier than at other parts, and the crack expands towards both sides and extends deeply as the internal pressure increasing. The inner core cracks at crown at one blow. There is a sudden change of stress at the corresponding position when crazing in pipe wall. The coating delamination is a conjunct result of the relaxation of prestressed wire, the internal and external difference in temperature and the shrinkage of the coating.At last, the anti-crack reliability is analyzed with the method of improved Support Vector Machine (SVM) response surface method. It is indicated that the concrete tensile strength and the concrete changeability, as well as the hydraulic pressure affect the anti-crack reliability obviously, otherwise, the influence of variation of section area of prestressed wire, effective prestressing and burying depth is not obvious correspondingly.