Flexural Behavior Of Ultra-High Performance Concrete Beams Prestressed With CFRP Tendons

The new materials of Carbon Fiber Reinforced Plastic (CFRP) and Reactive Powder concrete have good prospects in civil engineering. The excellent properties of CFRP and RPC make them revolutionary materials in the field of concrete technology, and RPC structures reinforced with CFRP tendons offer noticeable advantages, such as reducing dead load significantly and obtaining extreme durability and decreasing loss of prestressing force etc.An experimental study and the corresponding theory analysis are conducted to investigate the behavior of RPC structures reinforced with CFRP tendons under the financial support of Program"Ultra High Performance Concrete Prestressed with CFRP Tendons"of Natural Science Foundation of China and Program"High Performance Concrete Beams Prestressed with External CFRP Tendons"of Excellent Young Teachers Program of Ministry of Education of China. The purpose of the dissertation is to propose a new reinforced concrete type, such as good ductility, super durability, lighter structure, as well as less maintenance etc. This dissertation involves the following work:1. The material property test of CFRP tendon including relaxation test and tensile test under hot water curing are conducted. The test results show the relax loss of CFRP tendon is small, the relax ratio is 1.9% for 288h; the tensile strength of CFRP tendon doesn't reduce under hot water curing at 80±2℃for 48 hours.2. The uniaxial complete stress-strain curve in compression of RPC is obtained by a simple experimental technique. The constitutive model is suggested based on the test values of RPC which show that RPC is of good deformation capacity, the strain at peak stress and ultimate strain of RPC used in this paper is around 3500με, 4500με, respectively.3. Four normal concrete beams prestressed with CFRP tendons, 6 RPC beams prestressed with steel strand and 6 RPC beams prestressed with CFRP tendons are investigated. The detailed studies and corresponding analysis on the flexural behaviors, strain distribution, stress increment in prestressing tendons, failure modes as well as the crack pattern are conducted. The prestressed RPC beams have better ductility and deformation capacity, and the ultimate deformation can be 1/34～1/42 of span for RPC beams prestressed with steel strands, and 1/30～1/70 of span for RPC beams prestressed with CFRP tendons.4 The crack distribution of tested beams is analyzed. RPC beams exhibit tightly spaced cracking. Based on the Gergely-Lutz crack width equation, the crack width prediction of RPC is adjusted by strain ratio of the RPC to normal concrete. And the crack width prediction of FRP prestressed beams is adjusted by a coefficient which accounts for the degree of bond between FRP bars and surrounding concrete and the modulus of ratio of the steel to the FRP tendon. The predicted values are correlated with the tested values.5 A method for evaluating the ductility of RPC beams prestressed with steel strand is presented using the nominal yielding strength. Ductility of FRP prestressed beams based on an energy concept is discussed.6 The numerical and simplified analysis based on the nonlinearly program is presented. And the program analysis of ductility and the ultimate deformation are studied.7 The predicted values of the failure mode, the crack moment, ultimate moment of beams and the ultimate stress in CFRP tendon are proposed. And it is verified that the predicted results from the model presented are in good agreement with the test ones.8 The behavior and economic comparison of normal concrete and RPC simple span bridge with T cross section located at some highway is conducted.