TORSIONAL BEHAVIOR OF CONCRETE BEAMS STRENGTHENED WITH ADVANCED COMPOSITE SHEETS

Abstract

This multipart thesis investigates the behavior of RC beams strengthened with CFRP sheet under torsion load. The first chapter presents a comprehensive introduction to the research. In Chapter 2, research regarding the torsional behavior of inverted tee-beams strengthened with carbon fiber reinforced polymer (CFRP) sheets when simultaneously subjected to shear- and flexure-combined loading, is presented. Both completely wrapping and side bonded are investigated as CFRP-strengthening schemes. The results show that the load carrying capacity of completely wrapped sheets is higher than that of the beams with side-bonded sheets. For the side-bonded beams, the cross-sectional area of CFRP controls the load-carrying capacity. Subsequently, Chapter 3 presents an investigation of the torsional behavior of reinforced concrete beams strengthened with CFRP sheets. Assorted retrofit schemes are implemented with the variable widths and numbers of single- and double-layered CFRP U-wraps. After loading 27 beams (3 unstrengthened and 24 strengthened), test data are collected to investigate the efficacy of these U-wrap configurations. The width and layer composition of the bonded sheets has the greatest impact on the capacity of the beams, whereas the number of U-wraps in the longitudinal direction is found to have no significant effect. Although the CFRP retrofit decreases structural ductility, the placement of the U-wraps impedes stiffness-reduction rates, reduces twist angles, and redistributes torque-induced stresses. The identified characteristic effective shear modulus of the strengthened beams demarcates the pattern of energy drops, which are replated to the degree of brittleness in failure. As far as effective strains are concerned, the applicability of existing equations is appraised, and a new expression is proposed through reliability theory and stochastic simulations. In addition, Chapter 4 presents the torsional behavior of hollow reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) U-wraps. Test parameters involve a variable wall thickness in the section and the width and spacing of the externally bonded CFRP sheets. An experimental program is conducted with 27 beams (3 unstrengthened and 24 strengthened) to examine their capacities, shear flows, and force distributions when incorporating a ratio of 0.27 to 0.46 between the areas of the hollow and gross cross-sections. Through a machine learning approach combined with stochastic simulations, design recommendations are proposed.