Circular Prestressing

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This onez a term paper for Circular Prestressing which is a part of Special Structures in Prestressed Concrete

Text of Circular Prestressing

PRESTRESSED CONCRETE: TERM PAPER: CIRCULAR PRESTRESSING Table of Contents 1 2 2.1 2.1.1 2.1.2 2.2 3 3.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 4 4.1 4.2 4.2.1 4.2.2 4.3 4.3.1 5 5.1 6

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Introduction............................................................................................................................................................................................ 2 Design Parameters................................................................................................................................................................................. 3 General Analysis ............................................................................................................................................................................... 3 Analysis at Transfer..................................................................................................................................................................... 3 Analysis at Service Loads ........................................................................................................................................................... 3 Design ................................................................................................................................................................................................. 3 Prestressed Concrete Pipes .................................................................................................................................................................. 3 Construction Methodology ............................................................................................................................................................. 4 Analysis .............................................................................................................................................................................................. 4 Longitudinal prestressing........................................................................................................................................................... 4 Circumferential prestressing ...................................................................................................................................................... 4 Self weight .................................................................................................................................................................................... 4 Transport and handling .............................................................................................................................................................. 4 Weight of fluid ............................................................................................................................................................................. 4 Weight of soil above .................................................................................................................................................................... 4 Circumferential prestressing ...................................................................................................................................................... 5

Liquid Storage Tanks ............................................................................................................................................................................ 6 Construction Methodology ............................................................................................................................................................. 6 Analysis .............................................................................................................................................................................................. 7 For base ......................................................................................................................................................................................... 7 For top ........................................................................................................................................................................................... 7 Design ................................................................................................................................................................................................. 8 Detailing Requirements .............................................................................................................................................................. 8

Ring Beams ............................................................................................................................................................................................. 8 Analysis .............................................................................................................................................................................................. 9 Conclusion .............................................................................................................................................................................................. 9

List of Figures Figure 1: Internal Forces under Service Conditions............................................................................................................................................. 2 Figure 2: Use of Buttress in Circular Prestressing ................................................................................................................................................ 3 Figure 3: Stress Profiles across Section................................................................................................................................................................... 5 Figure 4: Forces due to Vertical Loads ................................................................................................................................................................... 5 Figure 5: Stress profiles across the thickness ........................................................................................................................................................ 6 Figure 6: Circumferential Prestressing & Shotcreting Operation ...................................................................................................................... 6 Figure 7: Fixed Base and Free Top / Hinged Base and Free Top ....................................................................................................................... 7 Figure 8:Cross-section of a nuclear containment structure & typical layout of prestressing tendons at dome and ring beam junction8 Figure 9: Containment Structure, Kaiga Atomic Power Plant, Karnataka ....................................................................................................... 8 Figure 11: Forces in the ring beam.......................................................................................................................................................................... 9 Figure 10: Forces at the base of dome .................................................................................................................................................................... 9

RAHUL N.SOMPURA (UC2905), SCHOOL OF BUILDING SCIENCE & TECHNOLOGY, CEPT UNIVERSITY, AHMEDABAD

PRESTRESSED CONCRETE: TERM PAPER: CIRCULAR PRESTRESSING

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A Study on Circular PrestressingRahul N.Sompura, Student, School of Building Science & Technology, CEPT University, Ahmedabad ABSTRACT The term "circular prestressing" is employed to denote the prestressing of circular structures such as pipes and tanks where the prestressing wires are wound in circles. In contrast to this term, "linear prestressing is used to include all other types of prestressing, where the cables may be either straight or curved, but not wound in circles around a circular structure. In most prestressed circular structures, prestress is applied both circumferentially and longitudinally, the circumferential prestress being circular and the longitudinal prestress actually linear. The circumferential prestressing resists the hoop tension generated due to the internal pressure. The prestressing is done by wires or tendons placed spirally, or over sectors of the circumference of the member. The wires or tendons lay outside the concrete core. Hence, the centre of the prestressing steel (CGS) is outside the core concrete section. The following term paper tries to cover the basic concepts of Circular Prestressing along with the Design and Construction Methodology associated with its respective structures. Keywords: Circular Prestressing, Circumferential, Prestressed Concrete Pipes, Liquid Storage Tanks, Ring Beams 1 Introduction

When the prestressed members are curved, in the direction of prestressing, the prestressing is called circular prestressing. For example, circumferential prestressing in pipes, tanks, silos, containment structures and similar structures is a type of circular prestressing. In these structures, there can be prestressing in the longitudinal direction (parallel to axis) as well. Circular prestressing is also applied in domes and shells. The circumferential prestressing resists the hoop tension generated due to the internal pressure. The prestressing is done by wires or tendons placed spirally, or over sectors of the circumference of the member. The wires or tendons lay outside the concrete core. Hence, the centre of the prestressing steel (CGS) is outside the core concrete section. The hoop compression generated is considered to be uniform across the thickness of a thin shell. Hence, the pressure line (or Cline) lies at the centre of the core concrete section (CGC). The following sketch shows the internal forces under service conditions. The analy