Behaviour of GFRP Wrapped Beams Under Pure Torsion

Abstract

In the design of many concrete structural elements, torsion is signi cant and has to be considered. Structural elements subjected to torsion experience diagonal tension and compression and fails in a brittle manner. Brittle failure of elements is undesirable and could lead to an nonductile seismic behaviour of structures during earthquakes.There are various structural elements like beam supporting cantilever slab, beam curved in plan, skew bridges, spandrel beam, box girder, inverted T-beam supporting pre-cast slabs etc. are primarily subjected to torsional moment. For understanding behaviour of R.C. element under torsion and to nd torsional resistance of R.C. element various theories like skew bending theory, space truss analogy are developed which consider the e ect of concrete, longitudinal reinforcement and transverse reinforcement and GFRP wrapping. Fiber Reinforce Polymer (FRP) composites are emerging as an important construc- tion material for upgrading capacity of existing structure and for construction of new structure. The role of FRP in improving torsional strength of concrete is studied in this project. The objective of present project is to evaluate torsional strength of GFRP wrapped R.C. specimens. For analytical solution of R.C. beam subjected to torsion, Space truss analogy is used. Experimental work comprises of casting and testing of 22 specimen with di erent con guration of FRP wrapping. The cross sectional dimensions of the specimens are 150mm 150mm and length is 1.3m. Specimens are tested under pure torsion. The ultimate torque and angle of twist are measured. The torque and angle of twist behaviour is presented in graphical form. The role of longitudinal, transverse rein- forcement are evaluated and presented. vi Experimental evaluation shows brittle failure in plain concrete beam, while ductile failure in R.C. beams. In R.C. beams due to reduced spacing of transverse rein- forcement improves in torsional resistance. The increase of 28% in longitudinal steel increased torsional strength by 13.8%. The increase of 37.5% in transverse reinforce- ment increased torsional strength by 8.4% to 13.9%. GFRP wrapping has increased torsional strength of plain concrete beams by 80% to 104%. Di erent con guration of GFRP wrapping has increased torsional resistance of reinforced concrete beams by 36% to 70%. Out of di erent types of wrapping con gurations diagonal strip wrapping is more e ective in torsional resistance. Nonlinear nite element analysis of plain concrete beams and reinforced concrete beams is carried out using ANSYS. Comparison of nite element analysis results and experimental results shows 4% to 13% variations in ultimate torsional resistance of R.C. beams. The content of report is divided in to various chapters. Chapter 1 includes gen- eral introduction, objectives of study and scope of work. Chapter 2 presents the brief review of literature for torsion in R.C. beam and torsion in FRP wrapped R.C. beams. Theories for torsional behaviour like space truss analogy and skew bending theory are presented in chapter3 to evaluate the torsional resistance of R.C beam. Chapter 4 includes FE modeling and analysis of plain concrete and R.C. beam using ANSYS. Chapter 5 presents the experimental programme conducted on plain, R.C. and GFRP wrapped R.C.beams. The results and discussion are presented in chap- ter6. Finally summary, conclusions and future scope of work are included in chapter 7.