Enhancement of Torsional Resistance of R. C. Beams using Fiber Reinforced Polymer Composites

Abstract

The loading mechanism of beams located at the periphery of buildings which carry loads from slabs, joists and beams from one side of the member generates torsional forces that are transferred from the beams to the columns. The structural elements subjected to torsion show cracking if they are not designed and detailed properly. Further change in loading or deterioration of structural element cause the de ciency in torsion resistance. To strengthen such structural element in torsion, Fiber Rein- forced Polymer (FRP) composites can be used. FRP as an external reinforcement is used extensively to address the strength require- ments related to exure and shear in structural systems. But the strengthening of members subjected to torsion is yet to be explored. The main objective of the present project is to study improvement in torsional resistance of Reinforced concrete (RC) beam with di erent con guration of (GFRP) wrapping. The behaviour and perfor- mance of RC members strengthened with externally bonded GFRP sheets subjected to pure torsion and combined torsion and bending is presented in this project. An experimental investigation is conducted on the RC beams using GFRP wrapping. A total of 24 beams are cast. Ten beams are tested under pure torsion and fourteen beams are tested in combined torsion and bending. The cross sectional dimensions of the specimens are 150mm 150mm with 4-10 mm diameter longitudinal bars and 2 leg 8 mm diameter stirrups at 150 mm c=c. The length of the specimens tested under pure torsion is 1.3 m and length of the beams tested under combined torsion and bending is 1.7 m. Total 4 beams are designated as control specimens and twenty beams are strengthened by GFRP wrapping of di erent con guration. GFRP wrap- ping con gurations considered for beams under pure torsion are 300 mm central strip wrapping, Corner and strip wrapping at the location of stirrups, Corner and strip wrapping in between stirrups, Corner and diagonal strip wrapping. GFRP wrapping con gurations considered for beams under combined torsion and bending are complete longitudinal, complete transverse, vertical strips, diagonal strips, corner and vertical strips, Corner and diagonal strips. For control as well as for each con gu- ration of GFRP wrapping two specimens are prepared. Averages of results of two specimens are presented in report. For applying pure torsion as well as combined tor- sion and bending, support conditions to allow twisting and set-up to apply torsional moment are fabricated. A loading frame of 200 kN capacity is also developed and fabricated for applying torsion on specimens. Measurements are taken during test- ing of specimens include Angle of twist at interval of torque, Torsion at rst crack, Angle of twist at rst crack, Ultimate torque, Ultimate twist, Torque and twist at col- lapse, strain at interval of loading. Also the failure patterns of specimen are reported. Based on the test results presented in this project, it is observed that reinforced concrete beams wrapped with di erent con guration of GFRP wrapping exhibited signi cant increase in their cracking and ultimate strength as well as ultimate twist deformations. Corner and diagonal strip wrapping (CO&DS) is most e cient in enhancement of the torsional resistance of reinforced concrete beams compared to other GFRP con gurations when beams are tested in pure torsion, and combined torsion and bending. Corner and diagonal strip wrapping increased ultimate torque by 238.5% when beam is subjected to pure torsion. The beam with corner and Di- agonal strip wrapping (CO&DS) exhibited a maximum (110%) increase in cracking torque and maximum (117%) increase in ultimate torque when beam is subjected to combined bending and torsion.