Torsional behavior of reinforced concrete T-beams strengthened with CFRP strips

Torsion is resisted well by locked system of reinforcement, due to the blood nature of the torsion induced-shear flow stresses in a beam. Therefore, it will be more effective to have strengthening schemes, which are wrapped in closed form around the cross section. But strengthening with U wrap (three sides) or strengthening in the web and flange unconnectedly is more useful because of the unreachability of the entire cross section due to addition of flange in uniform beam - slab construction (T section of interior beam). This work aims at studying the strengthening of T beams in torsion by using carbon fiber reinforced polymer (CFRP). The CFRP laminates will be used for strengthening previous to loading. The experimental work includes investigation of twelve reinforced concrete T beams tested under pure torsion. The first beam was the reference beam, without CFRP. The second beam was a simple concrete beam. The remaining ten beams. Variables considered in the test program include; effect of flange strengthening, effect of fiber orientation (90 degrees or 45 degrees CFRP strips with respect to the longitudinal axis), effect of using additional longitudinal CFRP strips with transverse CFRP strips, effect of bolt anchoring CFRP strips in the web and flange and effect of continuous CFRP strips between web and flange (isolated T section). Test results were discussed based on torque - twist behavior, beam elongations, CFRP strain, concrete strain and influence of CFRP on cracking torque, ultimate torque and failure modes.