Research On Structural Performance And Durability Theory Of Prestressed Concrete Cylinder Pipe

The safety and durability of water pipelines are necessary to maitain social development and people to live and work in peace and contentment. In recent years, prestressed concrete cylinder pipe (PCCP) is widely used in large-scale water diversion project, such as South-to-North Water Diversion Project. Therefore, research on the bearing mechanism, failure modes, and durability safety of PCCP, which can ensure the safety and smooth operation of the production, has a very important theoretical and practical significance. In this paper, PCCP has been researched in two directions:the pipeline’s structural performance and the theoretical analysis of durability. The main research work carried out as follows:(1) The development process of PCCP structure design theory is reviewed, that calculating the current structure calculation theory of PCCP does not reflect the stress distribution along the wall thickness direction of PCCP, which is a multilayer structure. On this basis, the structure calculation method of PCCP has been improved. The perfection of load calculation theory and section stress analysis model, which conforms to the actual service environment of PCCP, are taken.(2) A two-dimensional PCCP finite element model reflecting the characteristics of cross-section, and a three-dimensional PCCP finite element model reflecting the characteristics of overall entity was established. In accordance with PCCP production process, the whole process of PCCP from manufacturing to the final destruction was simulated. Stress state and structural response of PCCP under various conditions was got. And comparing with the theoretical analysis and experimental results has proved the correctness of the finite element model and analysis methods. The relationship between layers in PCCP was reasonable considerred, by which the peelling and cracking mortar layer, as well as prestressing steel prestressing losses under various conditions was accessed.(3) By analyzing the effect of different depths and different water pressure on the performance of PCCP, the effects of different loads to the structure response of PCCP was studied. It was found PCCP has two different failure modes, which relates on the burying depth of pipeline. Deep buried PCCP would be destroyed by external pressure, and shallow buried PCCP would be destroyed by internal pressure. Current design codes only considered the limit state of PCCP under internal pressure. Under internal water pressure changes, the change rule of structure response was studied, and the process of destruction of structure was simulated. The failure mechanism and failure modes of PCCP under internal water pressure were studied. Combined with previous achievements of PCCP external pressure destructive testing research, the bearing capacity limit state equations of PCCP’s two failure modes were established, proved useful to current design codes by test examples.(4) The effection to structure properties of PCCP, of changing on the core concrete thickness, mortar layer thickness, steel cylinder position, steel cylinder thickness, wire diameter and wire spacing, was analyzed. The functional roles of mortar layer, prestressing steel, concrete and steel cylinder in PCCP was proposed. The affecting to the structural performance of structure size changing was studied. Some significant engineering conclusions which can guide PCCP structural components arrangement and structure designing were proposed. The structural optimization formula reflecting the relationship between the sizes changing and stress on critical sections were established.(5) A variety of factors degrading PCCP structural durability were analyzed. The erosion of chloride ions was considered most harmful to PCCP durability. PCCP life evaluation criteria and durability design methods based on chloride ion penetration were proposed. By studying the mechanism of chloride ion diffusion, it was discovered that chloride ion diffusing to PCCP is two-dimensional diffusion, and the radius of pipe, steel wire and cylinder has a significant impact chloride ion concentration in PCCP. Combined with cross-sectional characteristics of PCCP, chloride ion diffusion theoretical model and residual service life evaluation model of PCCP were established.(6) The corrosion properties of prestressing steel in chloride environment were studied. It was proposed that chloride ion diffusing to PCCP will cause corrosion of three results:partial prestressing loss, partial wire rust and fracture of wire. Three types of analysis model were established, which are PCCP partial prestressing loss model, partial wire corrosion model and wire breakage model. These models were used to study the effects of prestressing steel corrosion damage on structural performance of PCCP. It concluded that the prestressing steel corrosion will reduce the bearing capacity of PCCP, and significantly affect the PCCP durability.