Anchorage Zone Stress Mapping using ANSYS

Abstract

This paper presents a comprehensive analysis of stress development in the anchorage zone of prestressed post-tensioned concrete beams using the finite element method with ANSYS. Focusing on both concentric and eccentric loading scenarios, the study varies the loaded area ratio (k) to investigate its effect on stress distribution. The obtained results are meticulously compared with existing literature, enhancing understanding of the behaviour of anchorage blocks within prestressed concrete members. Beyond stress assessment, the study evaluates the performance and structural integrity of the anchorage zone, providing valuable insights for design optimization and construction practices.

Introduction

I. INTRODUCTION

Many studies have been carried out in pre-stressed concrete beams. Always a special consideration was given to the anchorage zone or end block in Post tensioned beams. The anchorage zone is the zone between the end of the beam and the section where only longitudinal stress exists.

In the post-tensioned concrete beams, a duct is formed inside the beam and prestressing cable is kept inside this duct. Once the concrete gets harden, prestressing cable is stressed and anchored at the end of beam that induces internal stresses in the concrete beam. The stress distribution inside the post-tensioned concrete beam is very complex, especially near the end of beam where prestressing cable is anchored. This zone is called as Anchorage Zone

In the past, few researchers attempted to analyse stress distribution in anchorage zone in post tensioned Concrete beam using different techniques, which include analytical techniques, experimental methods, and numerical methods. [1] 

A. Bursting Force

A portion of a pre-stressed member surrounding the anchorage is the end block. Through the length of the end block, pre-stress is transferred from concentrated areas to become linearly distributed fiber stresses at the end of the block. The theoretical length of this block, called the lead length is not more than the height of the beam. But the stress distribution within this block is rather complicated.

Figure 1. shows the lines of pressure transfer which spread out from the area bd along the end block. The length of end block is usually taken equal to d. these lines of pressure may be taken to act as individual slender strut.

The larger transverse dimension of the end zone is represented as yo. The corresponding dimension of the bearing plate is represented as ypo. For analysis, the end zone is divided into a local zone and a general zone.

The transverse stresses developed in anchorage zone are tensile in nature over a large length and since concrete is weak in tension as shown in figure 2. So  adequate reinforcement should be provided to resist this tension. Hence, from the point of view of designer, it is essential to have good knowledge of the distribution of stresses in the anchorage zone, so that he can provide an adequate amount of steel, properly distributed to sustain the transverse tensile stress [6]

The local zone is the region behind the bearing plate and is subjected to high bearing stress and internal stresses. The behaviour of the local zone is influenced by the anchorage device and the additional confining spiral reinforcement.

The general zone is the end zone region which is subjected to spalling of concrete. The zone is strengthened by end zone reinforcement. The transverse stress (σt) at the CGC varies along the length of the end zone. It is compressive for a distance 0.1yo from the end and tensile thereafter, which drops down to zero at a distance yo from the end.

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Conclusion

This study presents a comprehensive three-dimensional finite element analysis of the anchorage zone in post-tensioned prestressed concrete, utilizing the commercial software ANSYS. The analysis included investigations under both concentric and eccentric loading conditions, examining a range of values for the parameter k. Stress variations were meticulously studied and are comprehensively presented across different combinations of k and e. It was observed that. 1) Magnitude of maximum transverse tensile stresses measured along the axis of loading or along the loaded face reduces with the introduction of eccentricity in prestressing forces. 2) Difference in magnitude of maximum transverse tensile stress at e = 0.0 & e = 0.1 reduces with the increase in value of k.

References

[1] Meenakshi Chougade, “Analysis of stresses in Anchorage zone using ANSYS”, International Journal of Innovative Research in Science & engineering ISSN (online) 2347–320. [2] [2] K. T. S. Iyengar, “Two Dimensional Theories of Anchorage Zone Stresses in Post- Tensioned Prestressed Beams”, Journal of American Concrete Institute, Vol. 59, No. 10, 1962, pp 1443-1465. [3] K. T. S. Iyengar and M. K. Prabhakara, “Anchor Zone Stresses in Prestressed Concrete Beams”, ASCE, Journal of Structural Division, Vol. 97, No. 3, 1971, pp 807-824. [4] Dipindas, C.D., Prashanth, M.H., Lakshmy, P. (2021). “Analysis of Anchorage Zone Stresses in Post-tensioned Concrete Girders” In: Narasimhan, M.C., George, V., Udayakumar, G., Kumar, A. (eds) Trends in Civil Engineering and Challenges for Sustainability. [5] Monika Jain, Rajendra Khapre “Post-tensioned anchorage zone: A review” Institution of structural engineers [6] Krishna Raju “Prestressed Concrete” Tata Mc-Graw-Hill Publishing Company, Delhi 2008 edition Page No 364-378 [7] S. Ramamrutham & R. Narayan “Strength of Materials” Dhanpat Rai Publishing Co. Edition 2001 Page No.371-388 [8] ANSYS Structural Analysis Guide ANSYS Release 9. ANSYS, Inc. Southpointe 275 Technology Drive Canonsburg, PA http://www.ansys.com (T) 724-746-3304 (F) 724-514-9494. [9] IS: 1343-1980: Indian Standard Code of Practice for Prestressed Concrete. 1st Rev. Bureau of Indian Standards, New Delhi, 1981

Copyright

Copyright © 2024 Ajinkya Shrikant Dixit. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.