Softened Truss Model for FRP Strengthened RC Members Under Torsion Including Tension Stiffening Effect

  • Mukesh Kumar Ramancha
  • T. Ghosh Mondal
  • S. Suriya PrakashEmail author
Conference paper


This paper presents an analytical model for prediction of torsional behavior of reinforced concrete beams strengthened with fiber reinforced plastics (FRP). Improved model proposed in this study is based on softened truss model (STM) which was developed to predict the response of reinforced concrete (RC) members under torsional loading. Tensile strength of concrete being very low, its contribution to torsional capacity of a RC member was neglected in the original STM. However, previous studies have suggested that neglecting tension stiffening may lead to considerable discrepancies in STM predictions. Therefore, in the present study the original STM has been modified to include the effect of tension stiffening for improved predictions of FRP strengthened RC beams. The developed model has been validated with experimental data obtained from literature. The proposed model shows the contribution of externally bonded FRP to the torsional capacity of RC members in addition to enhancing the ductility and is well supported by the experimental results. RC beams with two different FRP configurations, i.e. continuously wrapped and strip wise wrapped, were considered in this study. The analytical prediction of the overall torque-twist behavior compare favorably with the test data. The developed model can also be used for future parametric studies on FRP retrofitted RC beams under torsion.


Torsional Softened truss FRP Stiffening Torque-twist 


  1. 1.
    Ameli M, Ronagh HR, Dux PF (2007) Behavior of FRP strengthened reinforced concrete beams under torsion. Compos Constr 11(2):192–200CrossRefGoogle Scholar
  2. 2.
    Belarbi A, Hsu TTC (1995) Constitutive laws of softened concrete in biaxial tension-compression. ACI Struct J 92(5):562–573Google Scholar
  3. 3.
    Chalioris C (2007) Analytical model for torsional behavior of reinforced concrete beams retrofitted with FRP materials. Eng Struct 29(12):3263–3276CrossRefGoogle Scholar
  4. 4.
    Chalioris C (2008) Torsional strengthening of rectangular and flanged beams using carbon fibre reinforced-polymers-experimental study. Constr Build Mater 22(1):21–29CrossRefGoogle Scholar
  5. 5.
    Collins MP, Mitchell D (1991) Prestressed concrete structures, Response publications, Canada pp 766Google Scholar
  6. 6.
    Deifala AF (2007) Behavior and strengthening of RC T-girders in torsion and shear. Ph.D. thesis, Department of Civil Engineering, McMaster University, Hamilton, Ontario, CanadaGoogle Scholar
  7. 7.
    Deifala AF, Ghobarah A (2005) Simplified analysis for torsionaly strengthened RC beams using FRP. In: Proceeding of the international symposium on bond behavior of FRP in structures, BBFS 2005, International Institute for FRP in constructionGoogle Scholar
  8. 8.
    Ghobarah A, Ghorbel MN, Chidiac SE (2002) Upgrading torsional resistance of reinforced concrete beams using fiber-reinforced polymer. J Compos Constr 6(4):257–263CrossRefGoogle Scholar
  9. 9.
    Hsu TTC, Mo YL (1985) Softening of concrete in torsional members-theory and tests. J Am Concr Inst Proc 82(3):290–303Google Scholar
  10. 10.
    Hsu TTC (1993) Unified theory of reinforced concrete. CRC, Boca Raton (Fl)Google Scholar
  11. 11.
    Jeng CH, Hsu TTC (2009) A softened membrane model for torsion in reinforced concrete members. Eng Struct 31(9):1944–1954CrossRefGoogle Scholar
  12. 12.
    Kozonis D (1997) Strength evaluation and retrofit of reinforced concrete beams subjected to pure torsion. M.Sc. thesis, Department of Civil Engineering, RICE University, Huston, TexasGoogle Scholar
  13. 13.
    Mondal TG, Prakash SS (2014) Effect of tension stiffening on the behaviour of square RC column under torsion. Magazine of Concrete Research, ICE Publishing, UK (Accepted)Google Scholar
  14. 14.
    Panchacharam S, Belarbi A (2002) Torsional behavior of reinforced concrete beams strengthened with FRP composites. In: Proceedings 1st FIB congress, JapanGoogle Scholar
  15. 15.
    Salom PR (2001) Spandrel beams retrofitted with carbon fibre polymer and subjected to torsion. MSc thesis, Civil Engineering Department, University of North Carolina at Charlotte, Charlotte, N. CGoogle Scholar
  16. 16.
    Vintzileou E, Panagiotidou E (2008) An empirical model for predicting the mechanical properties of FRP-confined concrete. Constr Build Mater 22(8):841–854CrossRefGoogle Scholar

Copyright information

© Springer India 2015

Authors and Affiliations

  • Mukesh Kumar Ramancha
    • 1
  • T. Ghosh Mondal
    • 2
  • S. Suriya Prakash
    • 2
    Email author
  1. 1.Indian Institute of Technology, Guwahati (IITG)GuwahatiIndia
  2. 2.Indian Institute of Technology, Hyderabad (IITH)HyderabadIndia

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