Lecture Note –18 Indian Institute of （18 印度理工学院上课笔记）.pdf

86 Lecture Note – 17 PRESTRESS CONCRETE Code: IS1343: 1980 Introduction: Definition of Prestress: Prestress is defined as a method of applying pre-compression to control the stresses resulting due to external loads below the neutral axis of the beam tension developed due to external load which is more than the permissible limits of the plain concrete. The pre- compression applied (may be axial or eccentric) will induce the compressive stress below the neutral axis or as a whole of the beam c/s. Resulting either no tension or compression. Basic Concept Prestressed concrete is basically concrete in which internal stresses of a suitable magnitude and distribution are introduced so that the stresses resulting from the external loads are counteracted to a desired degree. Terminology 1. Tendon: A stretched element used in a concrete member of structure to impart prestress to the concrete. 2. Anchorage: A device generally used to enable the tendon to impart and maintain prestress in concrete. 3. Pretensioning: A method of prestressing concrete in which the tendons are tensioned before the concrete is placed. In this method, the concrete is introduced by bond between steel concrete. 4. Post-tensioning: A method of prestressing concrete by tensioning the tendons against hardened concrete. In this method, the prestress is imparted to concrete by bearing. Materials for prestress concrete members: 1. Cement: The cement used should be any of the following (a) Ordinary Portland cement conforming to IS269 (b) Portland slag cement conforming to IS455. But the slag content should not be more than 50%. (c) Rapid hardening Portland