FE model for simulating wire-wrapping during prestressing of an embedded prestressed concrete cylinder pipe

Abstract

A new 3D FE model, called wire-wrapping model, is proposed to simulate the process of wrapping wire for the prestressing of an embedded prestressed concrete cylinder pipe. This model is described in detail for its presentation and applied to a practical project for the prestressing simulation. The results obtained using this model are analyzed and compared with those obtained using the equivalent external radial pressure method and those using the AWWA C304 standard for its verification. Finally, the characteristics and contributions of this model are specified.

Introduction

Prestressed concrete cylinder pipe (PCCP) was widely used in the world during the last few decades for water conveyance in many areas like municipal, industrial, plant piping systems, etc. Two types of PCCP are produced: lined and embedded. In recent years, some significant projects such as the Great Man Made River (GMMR) in Libya and the South-to-North Water Diversion (SNWD) in China required extremely large diameter embedded PCCP for water transmission. So, most research has been focused on the performance of embedded PCCP for their larger size compared with the lined type. This type of PCCP is compressed by a helical high-strength wire. The wire is wrapped under high tension around a core composed of a steel cylinder encased in concrete. A mortar coating is applied to the exterior of the pipe to protect the wires from corrosion. As we all know, the wire in the PCCP is used to produce compressive prestress in the core that offsets the tensile stresses from loads and pressure. So, the wire should bean important load-bearing component and has a significant influence on the structural integrity of a PCCP. Lots of investigations showed that most failures of PCCPs could be attributed to the loss of prestress due to wire breaking [1].

Recently, FE analysis has been used to study the performance of a PCCP subjected to a combination of many types of loads and pressure, although it is well known that FEA is a difficult method to implement because of the composite structure of the PCCP. Generally, the effects of the wire component on the results of the FE analysis must be considered since the wire is an essential component of the structure as mentioned above. In addition, the simulation of prestressing is pivotal and complicated and can significantly affect the results obtained for the PCCP structure. Currently, some traditional equivalent methods such as those that employ an equivalent external radial pressure, equivalent temperature descent, initial stress, or initial strain are adopted in simulating the prestressing; however, each has its disadvantage.

The equivalent external radial pressure method is popular in engineering and is a conventional approach for simulating the prestressing of a PCCP. The method was proposed by Zarghamee et al. [2], [3], [4], Diab and Bonierbale [5], Gomez et al. [6], and Lotfi et al. [7] among others. This method considers a thin layer of wire so that the stiffness of the wire contributing to the pipe structure is not taken into account and the wire cannot bear any load. Using this method, the composition of the wire and the relation between the stress of the wire and the prestress of the PCCP cannot be considered, and neither can the interaction between the wire and concrete.

Studies by Zhang [8] and Lin [9] included the wire component in the pipe model and used the equivalent temperature descent method for applying prestress, which considers the contribution of the wire stiffness, but the results did not agree well with what is seen in practice. Although the stress of the wire after the temperature descent meets the demands of prestressing, the strain of the wire can be compressive, which is not the case in practice, and thus the wire–concrete interaction is not correctly addressed.

Lin [9] also employed the initial strain method to simulate the prestressing by prescribing the initial strain corresponding to the prestress of the wire. However, this method is suitable only for analysis of part of the cross section rather than the entire cross section. The initial stress method is an intuitive approach for applying prestress and is easily understood by researchers. However, a calculation of the equilibrium iteration should be conducted behind the definition of the initial stress since the initial stress state of the wire and concrete core cannot be an exact equilibrium state for the FE model. In the framework of elasticity, it is easy to achieve an equilibrium state, whereas when the nonlinearity of materials and the interaction is considered, the equilibrium calculation is too difficult to complete.

The objective of this paper is to propose a new 3D FE model using ABAQUS software, called the wire-wrapping model, which is used to simulate the process of wrapping wire for the prestressing of an embedded PCCP. This model is applied to an embedded PCCP with a diameter of 4 m used in the SNWD project for the prestressing simulation. The results obtained using the wire-wrapping model are analyzed and compared with those obtained using the equivalent external radial pressure method and those using the AWWA C304 [10] standard for its verification.