Posttensioned concrete

Posttensioned Concrete This material is frequently used for tanks to about 57,000 m (15 X 10 gal), usually containing water. Their design is treated in detail by Creasy (Pre.stre.s.sed Concrete Cylindrical Tanks, Wiley, New York, 1961). For the most economical design of... 

Prestressed (posttensioned) concrete tanks cost about 20 percent more than steel tanks of the same capacity. Once installed, however, concrete tanks require veiy little maintenance. A true comparison with steel would, therefore, require evaluating the maintenance cost of both types. 

Ban S. et al. Anchorage zone stress distributions in posttensioned concrete members. Proceeding World of Conference, Prestress. Concrete, San Francisco, July 1957, 16.1-1 6.14. 

PCI Journal (PCI) (0887-9672). The leading international source on the use of prestressed and posttensioned concrete. 

Concrete pressure vessels may be used in applications that require large sizes. Such vessels, if made of steel, would be too large and heavy to ship. Through the use of posttensioned (prestressed) concrete, the vessel is fabricated on the site. In this construc tion, the reinforcing steel is placed in tubes or plastic covers, which are cast into the concrete. Tension is applied to the steel after the concrete has acquired most of its strength. 

In the present discussion, reinforced concrete and prestressed concrete corrosion control methods are combined. Although prestressed concrete bridges have special concerns such as anchorage in both posttensioned and pretensioned structures and ducts for post-tensioned structures, the general corrosion control methods are applicable to both prestressed and conventional reinforced bridges. 

Post-tensioning is the process of casting the concrete wdth ducts in. After the concrete has hardened and developed sufficient strength cables in the ducts are tensioned and anchored. Ducts may be filled with cement grout (bonded) or with protective grease (unbonded). The grouting process is vital to the corrosion protection of the posttensioning cables. 

Structural materials—Materials for foundations can be timber, precast concrete, cast-in-place concrete, compacted dry concrete, grouted concrete, posttension steel, H-beam steel, steel pipe, composite, etc. 

Prestressing steel (see typical stress-strain diagram in Fig. 3) is used in external tendons (posttensioning) in the form of strands or wires or bundle of monostrands (inside corrugated metal or plastic ducts or inside smooth steel or plastic pipes) in concrete stmctures. 

Active confinement, and its subsequent beneficial effects, has also been achieved by means of prestressed metal strips. Recently, posttensioned metal straps were used to retrofit a full-scale reinforced concrete structure tested in shake table (Garcia et al. 2014). Also, unbonded high-strength steel wire was used to passively confine concrete cylinders. Typical curves for prestressed straps or high-strength wire spirals are illustrated in Fig. 2. 

Seismic Anaiysis of Concrete Bridges Numericai Modeiing, Fig. 1 Pier region of a bridge with deck consisting of precast posttensioned beams and cast in situ slab continuous over the piers... 

Another technique, in which stresses are applied after the concrete hardens, is appropriately called posttensioning. Sheet metal or rubber tubes are situated inside and pass through the concrete forms, around which the concrete is cast. After the cement has hardened, steel wires are fed through the resulting holes, and tension is applied to the wires by means of jacks attached and abutted to the faces of the structure. Again, a compressive stress is imposed on the concrete piece, this time by the jacks. Finally, the empty spaces inside the tubing are filled with a grout to protect the wire from corrosion. 

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