Shear-torsion interaction of RC beams strengthened with FRP sheets

One of the most common options for structural strengthening and rehabilitation is the use of FRP sheets for shear-torsion strengthening of reinforced concrete beams (RCBs). Their widespread use owes much to their ease of application in addition to many other advantages. The availability of technical references and construction codes today make it easy to calculate the shear and torsion capacities of strengthened beams. Practically, however, it is the combined shear and torsion rather than pure torsion that develops in beams. The present article investigates the use of FRP sheets in strengthening RC beams. For the purposes of this study, 14 RC beams were used that were classified into three different sets: one set consisted of 5 non-strengthened (plain) beams and two sets (one with 5 and the other with 4 beams) consisted of RC beams strengthened with CFRP sheets in two different strengthening patterns. The shear-torsion interaction curves were derived for them by loading the beams under a variety of eccentricities ranging from 0 (pure shear) to infinity (pure torsion). The supports were constructed with flexure and torsion rigidity. Laboratory tests revealed that the shear-torsion interaction curves for all the three sets of beams were close to straight lines.