Prestressing systems

In many vessels only unbonded systems have been adopted. This choice is based on a condition that all tendons must be inspected for defects including those due to corrosion. The advantages or disadvantages of bonded and unbonded tendons are fully discussed [200] by the author. 

The liner in general is to protect concrete from excessive reactor temperatures and radiation developed from inside. It carries cooling pipes circulating water at suitable intervals. The liner is anchored to the concrete by means of plugs, etc. The details are given later on under a separate caption. 

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In addition, FE simulation is applied to determine load-adapted tool layouts by modeling the die insert and the prestressing system. This helps to enhance tool life and to reduce tool failure by overload and fatigue. Especially in 2D axially symmetric FE models, a combined modeling of workpiece and tool, including the prestressing... 

Burrow, R. E. D. and Brunton, J. D. Developments in large prestressing systems for nuclear pressure vessels. FIP Sixth International Congress. Prague, 1970. 

The state-of-the-art review of the prestressed concrete reactor vessels covers, in this chapter, historical development, the available methods of analysis and design procedures of vessels and their elements such as concrete, prestressing systems, conventional steel, vessel steel liner and anchorages including penetration liners. Each section is presented with a clear-cut discussion on its contents. 

The experimental tests have been carried out on two pressure vessel models, namely that of Dungeness B and Oldbury, both cylindrical with top and bottom flat caps, with different prestressing systems, indicate different modes of failure. These will be the reference models of the limit state analysis which has been developed in the text and which will be finally provided by using 3D hybrid finite element analysis under increasing gas load pressure. The Oldbury will be given a detailed assessment later on in the text. 

Figures 5.1, 5.2, 5.3, 5.4 and 5.5 show the prestressing systems adopted or recommended for the several existing and future vessels. Table 5.1 shows a summary of equations in case of wire-winding for obtaining axial, circumferential, radial and boundary pressures. Details and geometry of each vessel are given in several references [13-15].

Figures 5.2, 5.3, 5.4, 5.5 and 5.6 show typical layouts of prestressing systems for existing prestressed concrete vessels.

Prestressing systems would be able to avoid completely a premature failure either in the primary zones or in local areas. Under such conditions greater emphasis can be laid on the control of cracking by using good quality bonded steel. 

This failure mechanism is different from that predicted for the Dungeness B vessel, although they both have an identical shape and reactor system layout but with different prestressing system and gas design pressure. 

Appendix C gives data on various prestressing systems. 

Generally, high-strength concrete is used for prestressed concrete work. The steel used in prestressed concrete is generally of a much higher strength than mild steel. This aspect is discussed later on in the choice and evaluation of prestressing systems. 

Typical layout of prestressing systems. Oldbury (With compliments from Sir Robert McAlpine.)... 

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