Torsional Strengthening of Low-Strength RC Beams with Post-Tensioned Metal Straps: An Experimental Investigation


  • Monthian SETKIT School of Engineering and Technology, Walailak University, Nakhon Si Thammarat 80160, Thailand
  • Thanongsak IMJAI Center of Excellence in Sustainable Disaster Management, Walailak University, Nakhon Si Thammarat 80160, Thailand
  • Udomvit CHAISAKULKIET Department of Civil Engineering, Rajamangala University of Technology Rattanakosin, Nakhon Pathom 73170, Thailand
  • Reyes GARCIA School of Engineering, The University of Warwick, Coventry, UK
  • Komsan DANGYEM School of Engineering and Technology, Walailak University, Nakhon Si Thammarat 80160, Thailand
  • Katipoj SANUPONG School of Engineering and Technology, Walailak University, Nakhon Si Thammarat 80160, Thailand
  • Weerasit CHAMNANKIT School of Engineering and Technology, Walailak University, Nakhon Si Thammarat 80160, Thailand



Torsional strengthening, Low strength concrete, Post-tensioned metal straps, Active confinement, Torsion, Steel straps, Strengthening


This article investigates the behaviour of low-strength reinforced concrete beams under pure torsion with and without strengthening. Four beams were cast and tested in torsion: i) a control beam without vertical reinforcement, ii) two beams with internal stirrups designed for shear and torsion demands using different stirrup spacing (50 and 100 mm), and iii) a beam having steel stirrups with a spacing of 100 mm strengthened using high ductile post-tensioned metal straps (PTMS). The main objective of the PTMS strengthening solution was to investigate the enhancement of torsional strength confined along the beam. The failure modes, torsional capacities, rotation, and strengthening performance in torsion are discussed in in this study. The experimental results indicate that the PTMS improved the cracking torque capacity by up to 15 % compared to the control beam. Moreover, the PTMS also increased the ultimate torque by up to 19 % compared to the unstrengthened beam. Current code equations to predict the torsional capacity of RC beams are also compared with the experimental results. It is found that the predictions obtained by current ACI equation gives a good agreement and yield in general conservative values compared to the experimental ones.


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How to Cite

SETKIT, M. ., IMJAI, T. ., CHAISAKULKIET, U. ., GARCIA, R. ., DANGYEM, K. ., SANUPONG, K. ., & CHAMNANKIT, W. . (2020). Torsional Strengthening of Low-Strength RC Beams with Post-Tensioned Metal Straps: An Experimental Investigation. Walailak Journal of Science and Technology (WJST), 17(12), 1399–1411.