International Concrete Abstracts Portal

The simple-supported concrete beams reinforced with aramid FRP (AFRP) rods and carbon FRP (CFRP) sheets were tested to failure using a symmetric two-point concentrated static loading system. AFRP rods were used instead of steel reinforcing bars, and CFRP sheets were epoxy bonded to the tension face of the concrete beams to enhance their flexural strength. Moreover, a 5-cm wide strip of CFRP sheet in some places were wrapped around the web (hereafter, called “U-jacket”) after the CFRP sheets were bonded. The strain distributions on AFRP rods and CFRP sheets, and flexural behavior of the beams with AFRP rods and CFRP sheets were examined experimentally. The results showed that; 1) peeling of CFRP sheets occurred near the maximum flexural moment region, 2) ultimate load and deflection of the beam with U-jackets were higher, and 3) the U-jacket was a significant factor affecting the ductile behavior of beams with CFRP sheets.

In addition to the conventional modes of failure observed in RC beams, new ones can be detected in RC members strengthened by means of externally bonded FRP reinforcement. Concrete cover delamination is a mode of failure caused by shear transfer and local regions of tension stress fields. A series of tests were carried out in order to study the concrete cover delamination failure, wherein the variables were length of beam span, bonded area, number of plies, and U-jacketing schemes. Two mechanisms within the concrete cover delamination failure were observed: one starting at the cutoff point of the FRP, which is originated by a high concentration of normal (out-of-plane) and shear stresses, and second one starting at an intermediate crack. The latter mode of failure is caused by normal and shear stresses at the level of the steel reinforcement. From the point of view of design, it is important to recognize this premature type of failure, and determine algorithms for its prediction.

When the serviceability or ultimate strength of a reinforced or prestressed concrete beam is assessed to be inadequate, fibre reinforced polymer (FRP) sheets may be suitable for strengthening these beams. FRP sheets exhibit high strength-to-weight ratios and are non-corrosive. When bonded to the tensile face of a concrete beam, FRP sheets supplement the flexural reinforcement of the beam, increasing the beam’s strength. To improve the efficiency of this strengthening technique, FRP sheets may be applied with an induced prestress. This paper presents results from an on-going experimental investigation that examines the effectiveness and feasibility of using prestressed carbon fiber reinforced polymer (CFRP) sheets to increase the capacity and improve the serviceability of damaged concrete members. A practical mechanical anchorage system for prestressing the CFRP sheets against the concrete beam is presented and the results of the prestressing process are discussed. The flexural behaviour of one 4.5 metre T-section prestressed concrete beam strengthened with prestressed sheets and loaded to failure at room temperature (22×C) is presented and compared to that of an unstrengthened control beam. The paper describes the on-going investigation into the behaviour of beams strengthened with prestressed CFRP sheets and tested at low temperature (-27×C). Aspects of the research program related to the long-term behaviour of beams strengthened with prestressed FRP are also discussed.

In this paper, a new method to use Carbon Fiber Sheets(CFS) which is prestressed before they are bonded to the concrete surfaces based on the concept of prestressing technique is developed. A prestressing system is first designed to be suitable for strengthening existing concrete structures. An experimental program is carried out to verify the reinforcement effects of beams such as on the improvements of flexural strength, ductility, stiffness and crack resistance. To avoid the debonding failure near the ends upon releasing the pre-tensioned force, the anchorage zone are dealt with by several proposed reinforcing methods and the effects of anchorage treatments are also discussed. An effort is also made to investigate the determination of appropriate presressing stress level of CFS and structural optimization of reinforcement.

In this paper, uniaxial tension tests on CFS(carbon fiber sheet)-strengthened concrete specimens with and without steel bar reinforcement and bending tests on CFS strengthened RC beams were conducted to examine the crack behavior in the concret. The testing showed that the crack spacing of the uniaxial tension members strengthened with CFS was only slightly affected by the diameter of the reinforcing steel bars, the thickness of the concrete covering and the stiffness of the CFS. The crack spacing and the crack width both for tensile and flexural members was significantly smaller when the CFS was used. And also the cracks were distributed in the plain concrete tension member without steel reinforcement strengthened with CFS. Finally, it was recognized that the tension stiffening effect is realized to be improved by the non-liner behavior of the CFS-concrete interface.