Technical English Week 9 Unit 8 Section 1

Technical English Week 9: Unit 8 Section 1: Reading Comprehension Shahrood University of Technology English for Civil Engineering Students 1

Prestressing with Post Tensioned Tendons • When a member is fabricated in such a manner that the tendons are stressed, and each end is anchored to the concrete section after the concrete has been cast and has attained sufficient strength to safely withstand the prestressing force, the member is said to be post tensioned. Two types of tendons are used: bonded and unbonded. English for Civil Engineering 2 Students

• Fully bonded post tensioned tendons consist of bars, strands, or wires, in preformed holes, metallic ducts, or plastic tubes, that have been pressure groutedafter stressing. The tube is used to prevent the tendon from becoming bonded to the concrete at the time that the concrete is placed. English for Civil Engineering Students 3

• After the concrete has been sufficiently cured, the tendon is stressed, and the tube is injected with grout. The cured grout effectively bonds the tendon to the tube and the concrete itself (the outside surface of the tube becomes bonded to the concrete when the concrete is placed). English for Civil Engineering Students 4

• Rather than using metallic tubes, bonded tendons can be constructed by using holes formed in the concrete with removable rubber tubes or hoses; in this method the tendons are inserted into the preformed holes after the rubber tubes have been removed, and they are subsequently stressed and grouted. English for Civil Engineering Students 5

• Another form of bonded tendons which may or may not be partially bonded to the concrete section, and are commonly known as external tendons is used in special applications. English for Civil Engineering Students 6

• Unbonded tendons normally consist of strands or wires that are wrapped or encased in plastic after having been coated with grease or a bituminous material. The grease sometimes contains a rust inhibitor to help protect the tendons from corrosion. English for Civil Engineering Students 7

• Also, waterproof paper wrapping has been used rather than plastic. Unbonded tendons normally are assembled in a factory, shipped to the job site, and placed in the forms before the concrete is placed. They are not grouted after they have been stressed, so they do not become bonded to the concrete. English for Civil Engineering Students 8

• Bonded tendons are generally used in bridge construction, but unbonded tendons have been so used quite successfully. Unbonded tendons are most frequently used in building construction, but bonded tendons are sometimes used there also. The quantity of unbonded tendons used annually greatly exceeds the amount of bonded tendons used. English for Civil Engineering Students 9

• Post tensioning offers a means of prestressing on the job site, which may be necessary in some instances. Very large building or bridge girders that cannot be transported from a precasting plant to the job site (because of their weight, size, or the distance between the plant and the job site) can be made by post tensioning on the job site. English for Civil Engineering Students 10

• Post tensioning is used in precast as well as in cast in place construction. In addition, fabricators of pretensioned concrete will frequently post tension members for small projects on which the number of units to be produced does not warrant the expenditures required to set up pretensioning facilities. English for Civil Engineering Students 11

• In post tensioning, it is necessary to use some type of device to attach or anchor the ends of the tendons to the concrete section. Such devices usually are referred to as end anchorages or simply anchorages. The end anchorages, tendons, special jacking, and grouting equipment, if used, in post tensioning concrete are collectively referred to as a post tensioning system. There are several different systems in use. English for Civil Engineering Students 12