This paper presents the torsional behavior of R.C. beams strengthened with externally steel
stirrups, steel links and Fiber Reinforced Polymers (FRP) systems, R.C beams with web opening
subjected to pure torsion. A total six rectangular beams were tested. Two un-strengthened
specimens without and with web opening, which considered as control specimen, the rest four
beams with web opening which one specimens strengthened with external steel stirrups, one
specimen strengthened with steel links, one specimen strengthened with external stirrups made
from Glass Fiber Reinforced Polymer (GFRP), and one specimen strengthened with external
stirrups made from Carbon Fiber Reinforced Polymer (CFRP). All the beams were subjected to
pure torsion till failure. The type of strengthening material and system is the basic parameter in this
study. The experimental results showed a noticeable increase in torsion resistance for the
strengthened specimens compared to control specimen. In comparison with control beam, the
ultimate torsional moment increased up to 287% for beam strengthened with steel links, up to 134
% for beam strengthened with CFRP and increase capacity of beams with, and up to 100% for
beam strengthened with GFRP stirrups.
An analytical model was proposed and applied to predict the torsional strength of the tested RC
beams, the predicted strengths were found to be in good agreement with the experimental results.