Method of Pre-stress concrete can be made by two main categories: 1. Pretensioning In this method steel tendons, in the form of wires or strands, are tensioned between end-anchorages and the concrete members cast around the tendons. Once the concrete has hardened sufficiently, the end-anchorages are released and the prestress force is transferred to the concrete through the bond between the steel and concrete. The protruding ends of the tendons are then cut away to produce the finished concrete member. Pretensioned members usually have a large number of wires or strands to provide the prestress force, since the force Page 7 in them is developed by bond to the surrounding concrete, and as large an area of surface contact as possible is desirable.
Figure 1.9. This method is ideally suited to factory production since large anchorages are required to anchor all the tendons, and several members can be cast along the same set of tendons (Fig. 1.9). It is important to ensure that the members are free to move along the prestressing bed, otherwise undesirable tensile stresses may be set up in them when the end-anchorages are released. It is interesting to note the use of in situ prestressing in cable-stayed and suspension bridge construction. In the former, the stays are tensioned in order to reduce the deflections of the bridge and also to optimize the deck cross-section. Pretensioning of suspension bridge cables has also been employed to ensure that the grout used to protect them from corrosion remains in compression, and therefore crack-free, under all load conditions. Some examples of pretensioned members, other than beams, which are commonly produced are shown in Fig. 1.10.
Figure 1.10. Reference 1. M.k.Hurst. MSc, DIC, MICE, MIstruct.E, (1998). Prestressed concrete Design 2nd edition. If you want to read more on pdf download file below:
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