| 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 hi 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 after installation 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.4. Cover delamination or FRP debonding from RC beams strengthened with CFRP may result in premature failure in addition to the conventional failure modes observed in un-strengthened RC beams. The main objective of this study was to assess the effects offlexural cracks in the mid-span tension zone of the plated beams on interfacial stresses. The methods for calculating interfacial stresses of CFRP strengthened un-cracked and pre-cracked RC beams are proposed. Combining with CFRP-strengthened RC structures in use, the effects of delaminations or debondings on the structural applicability and reliability of the FRP system are studied. Results show that the Delaminations or air voids in FRP-strengthened structures affects not only the width of cracks, but also the rigidity of strengthened structures. Finally, general recommendations for CFRP design and installation are proposed for preventing or delaying premature failures of CFRP-strengthened beams.5. An experimental investigation on the performance of 3.1m long RC beams strengthened in shear with externally bonded CFRP strips is conducted. The experimental program consists of 19 simply supported beams. The parameters investigated in this study include shear...
|
PDF Full Text Request