Nonlinear Analysis Of CFRP Reinforced/Prestressed Concrete Beams

ABSTRACT:Due to its lightweight, high strength, corrosive resistance, fatigue resistance, CFRP can be expected to replace ordinary reinforcing steels in concrete structures which are in harsh environment, However, CFRP bars have linear relationship of tensile stress-strain until damage, without apparent yield steps. Moreover, CFRP bars have high tensile strength and low shear strength. So it's necessary to study the behavior of concrete beams reinforced and prestressed with CFRP bars.The behavior of four concrete beams was experimentally investigated in this paper. Three of them were reinforced with CFRP bars while the last one with steel bars as a reference beam. The number of the longitudinal tensile CFRP bars is the same for all CFRP-reinforced concrete beams. One of CFRP-reinforced concrete beams with positioning the CFRP-bars into single layer, one with positioning the CFRP-bars into single layer and placing circular heliced stirrups in compression zone, and another one with positioning the longitudinal tensile CFRP bars into two layers and placing circular heliced stirrups in compression zone. Test results have showed that the load-deflection curves of CFRP-reinforced concrete beams exhibit two stages, namely elastic and cracked-elastic stages, which is different with the three stages of the steel-reinforced concrete beam. Owing to the poor bond performance between the CFRP bars and concrete, for CFRP-reinforced beams, the number of cracks is limited, the space between cracks is large, and the cracks are wider. Such phenomena are similar to that of the unbonded prestressed concrete beams without non-prestressed steel.The deformability indexes of CFRP-reinforced beams are compared, it's shown that the beam which positioning the longitudinal tensile CFRP bars into two layers or placing circular heliced stirrups in compression zone has favorable deformability.The full-range behavior of concrete beams with FRP bras is numerically analyzed by using finite element software (OpenSees). In analysis, three kinds of concrete beams are included. There are concrete beams reinforced by CFRP bars, partially prestressed concrete beams with bonded AFRP tendons, and partially prestressed concrete beams with unbonded CFRP tendons. Compared with the test results, it is indicated that the selection of the element, the definition of the constitutive relations of the materials, the methods of modeling and convergence criteria are effective and correct.Parameter analysis is carried out for concrete beams with CFRP tendons by using OpenSees. The results indicate that, for concrete beams reinforced by CFRP bars, higher concrete strength and CFRP reinforcement ratio lead to better flexural property and deformability. While for partially prestressed concrete beams with CFRP tendons, with the increase of concrete strength, CFRP reinforcement ratio and tendon effective prestress, and the decrease of steel reinforcement ratio, the flexural properties of the beams are better. However, with the decrease of CFRP and steel reinforcement ratio and tendons effective prestress, the deformability of CFRP partially prestressed concrete beams are improved.