Strengthening Torsion Critical Reinforced Concrete Beam by Externally Bonded Carbon Fiber Reinforced Polymer: Analytical to Experimental Investigation

Addis Ababa University ABSTRACT Although there is an enormous amount of knowledge on behavior, design and detailing of reinforced concrete (RC) members for torsion, many structural members are found to be torsion critical. If a structural member becomes torsion critical, the available mitigations are either to strengthen or to demolish the structural component. Considering its economic implications, demolishing the structure element might not be feasible; as a result, strengthening becomes the only option. One method of strengthening a torsion critical member is by using externally bonded carbon fiber reinforced polymers (CFRP). While there is a great deal of work conducted on strengthening torsion critical members, most of the studies are limited to the case of pure torsion. Often, along with torsional moment, most of the torsion critical beams are subjected to associated shear and flexural moment. In this study, the effectiveness of the strengthening technique using CFRP is scrutinized by conducting experimental tests on specimens for the combined action of flexure and torsion. Furthermore, the thesis presented an analytical modeling of combined action using a proposed truss model (COMBINED-SMM-FRP). In the thesis, an additional comprehensive analytical study was conducted using nonlinear finite element packages DuCOM-COM3 and VecTor3. Additionally, the capability of the proposed analytical model (COMBINED-SMM-FRP) in predicting the response of fiber wrapped RC members under the action of combined torsion and flexure was also examined. The experimental, analytical and the nonlinear finite element studies showed the application of CFRP can substantially enhance the cracking and ultimate strength of torsion critical members. In the experimental investigation, an ultimate strength enhancement of more than 60 percent is observed for the strengthened specimen relative to their control specimens.Although there is an enormous amount of knowledge on behavior, design and detailing of reinforced concrete (RC) members for torsion, many structural members are found to be torsion critical. If a structural member becomes torsion critical, the available mitigations are either to strengthen or to demolish the structural component. Considering its economic implications, demolishing the structure element might not be feasible; as a result, strengthening becomes the only option. One method of strengthening a torsion critical member is by using externally bonded carbon fiber reinforced polymers (CFRP). While there is a great deal of work conducted on strengthening torsion critical members, most of the studies are limited to the case of pure torsion. Often, along with torsional moment, most of the torsion critical beams are subjected to associated shear and flexural moment. In this study, the effectiveness of the strengthening technique using CFRP is scrutinized by conducting experimental tests on specimens for the combined action of flexure and torsion. Furthermore, the thesis presented an analytical modeling of combined action using a proposed truss model (COMBINED-SMM-FRP). In the thesis, an additional comprehensive analytical study was conducted using nonlinear finite element packages DuCOM-COM3 and VecTor3. Additionally, the capability of the proposed analytical model (COMBINED-SMM-FRP) in predicting the response of fiber wrapped RC members under the action of combined torsion and flexure was also examined. The experimental, analytical and the nonlinear finite element studies showed the application of CFRP can substantially enhance the cracking and ultimate strength of torsion critical members. In the experimental investigation, an ultimate strength enhancement of more than 60 percent is observed for the strengthened specimen relative to their control specimens.