Comparison of Stresses for Circular and Rectangular Pre-stressing Plates in Post-Tensioned Anchorage Zone

Author Name(s): Monika R. Jain, Rajendra N. Khapre
Author Email: jainmr_3@rkned.edu

Abstract

This paper presents the case study on 3-dimensional analysis of end block of rectangular post tensioned concrete beam. The end block of post tensioned concrete beam is modelled in finite element based software ANSYS. Concentric prestressing force is applied on two different shapes of plates. A case study is performed in which the loaded area ratio is varied. The results obtained are compared in terms of transverse tensile stress, longitudinal tensile stress and bursting force for both circular and rectangular shape plate. The calculated bursting tensile force is also compared from IS 1343:2012.

Introduction

It is well establish fact that the basic economy of prestressed concrete lies in its high strength to weight and cost ratio, its resistance to fire and corrosion and its versatility and adaptability. In prestressed concrete members, stresses are induced during the construction in such a way that they can resist stresses caused by external applied loads. Prestressed structural member are widely used to achieve high strength at lower self-weight. Prestresed concrete is most suitable for long span structural element like beam and girder. Broadly there are two methods of prestressing namely Pre-tensioning and Post-tensioning. In pre-tensioning, the prestressing tendons are tensioned before the concrete is placed while in Post-tensioning hardened concrete is stressed by applying external loads. In Post tensioned concrete beams, a duct is formed inside the beam and prestressing cable is kept inside the duct. Once the concrete gets harden, prestressing cable is stressed and anchored at the end of beam that reduced internal stresses in the concrete beam. Post tensioning application include office and apartments building, parking structure, slab-on-ground, bridges, sport stadium, rock and soil. The anchorage zone is defined as the end portion of prestressed post-tensioned concrete beam starting from the loaded face to the section at a distance of d (depth of the beam) measured along the axis of the beam.

Conclusion

Based on computer simulation carried out on ANSYS on end block of post tensioned concrete beam, following conclusions are drawn. 1. From Case 1 and case 2 i.e. Geometry with circular shape and rectangular shape anchorage plate it is clear that there are very fine changes and differences between the results of circular and rectangular plate. Hence shape of anchorage plate does not influence the maximum tensile stress and the bursting tensile force of end block very much. 2. As the value of area ratio (k) increases the transverse tensile stress along the loaded face decreases from 0.1 to 0.5 also the position of zero stress shifted away from centre both the cases. 3. For longitudinal tensile stress as the value of area ratio (k) increases the stress along the longitudinal axis also increases for both circular and rectangular prestressing force.4. Study shows that as the value of area ratio increases the bursting force reduces. Also the bursting force calculated from present study gives very much less magnitude of bursting force when compared with the IS code values. 5. Results indicates that the cross section of prestressing plate does not influence the maximum transverse tensile stress, location of zero stress and also the bursting tensile force in anchorage zone.

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