Carbon Fiber Sheet Reinforced Concrete Beam Flexure

Reinforced concrete bridges become structurally deficient for several reasons, including corrosion of steel, increases in allowable truck weights, deterioration due to age and exposure to deicing salts. All these result in an urgent need to strengthen many of these bridges with an effective and reliable method. For numerous deteriorated, underrated, and overloaded aging bridges in our country, externally bonded carbon fiber reinforced polymer (CFRP) sheet is an efficient technique to retrofit or strengthen existing bridges due to their high tensile strength, light weight, resistance to corrosion, high durability, and ease of installation. Combining with the research program 'application of carbon fiber reinforced polymer (CFRP) for strengthening reinforced concrete bridges' of Shangdong province, the key techniques of application of CFRP composite to strengthen reinforced concrete bridges are studied. The major contents are mainly summarized as follow:1. An experimental investigation is conducted on the performance of 2.7m long reinforced concrete beams strengthened in flexure. The experimental program consist of nine RC beams with a rectangular cross-section of 150-mm-wide and 250-mm-deep. The variables investigated in this program include pre-cracking load, installation load level and tension reinforcement ratio. The experimental results indicate that strengthening pre-cracked beam with CFRP can not only enhance its stiffness, but also decrease crack width on the surface of beams and reduce tensile strain of steel.2. The method to define the ultimate limit state of carrying capacity , critical failure, critical strengthened quantity and critical height coefficient of concrete compressive region is suggested. Design algorithms in Specifications for Highway Bridges and Culverts(JTJ021 -85) format as well as Code for Design of Concrete Structures (GB50010-2002) format are proposed to predict the capacity of available beams strengthened in flexure with CFRP. Results show that the proposed design approach is conservative and acceptable.3. FRP systems have already used to strengthen concrete bridges, and there is an urgent need for information relating to the behavior and performance of these systems when they are applied to RC bridges. Load tests were conducted 'before' and 'after' installation of the laminate system. The main objectives were to evaluate, through the 'before' and 'afterinstallation load testing, effectiveness of the strengthening system and investigate its effect on structural behavior. Tests results indicate that strengthening RC integral bridges and simply-supported reinforced concrete bridges with externally bonded CFRP reinforcement can not only reduce the width of cracks and strains in concrete, but also improve the transverse load distribution in superstructure.