International Concrete Abstracts Portal

Current design methods for predicting deflections and crack widths at service load in concrete structures reinforced with steel bars may not be necessarily applicable in those reinforced with fiber reinforced polymer (FRP) bars. In this paper, methods for predicting deflections and crack widths and spacing of glass fiber reinforced polymer (GFRP) reinforced concrete beams were proposed. In order to use the effective moment of inertia for concrete beams reinforced with FRP bars, the effect of reinforcement ratios and elastic modulus of the FRP reinforcement were incorporated in Branson’s equation. This paper also presents a new equation to predict crack width. Six concrete beams reinforced with different GFRP reinforcement ratios were tested. Deflections and crack widths were measured and compared with those obtained by the proposed models. The comparison between the experimental results and those predicted was in good agreement.

This paper summarizes research findings on the use of carbon fibre reinforced polymer (CFRP) sheets for shear strengthening of pretensioned AASHTO bridge girders. The research includes an experimental program conducted at the University of Manitoba using scale models of pretensioned concrete girders in composite action with the deck slab. Seven ten meter long beams were strengthened with three different types of CFRP sheets using ten different configurations and were tested to failure at each end. The paper describes the experimental program, test results, failure mechanisms and the effectiveness of each configuration of CFRP sheets. A rational model is introduced to define the contribution of the CFRP sheets to the shear resistance in addition to the contributions provided by the stirrups and the concrete for I-shaped pretensioned concrete members. Test results are used to verify the proposed model.

The uniaxial tensile tests of Reinforced Concrete elements with Carbon fiber sheet (RCC) are conducted to clarify the basic mechanical characteristics which affect the tension stiffness of RCC. This paper mainly presents the difference between RCC and ordinary Reinforced Concrete member (RC) in the load carrying capacity, the average crack spacing, stress and/or strain distributions of steel, and the average stress – strain relationship of concrete. Crack spacing of RCC becomes smaller between 25% and 60% of that in RC as the amount of Carbon Fiber Sheet (CFS) increases. The strain distributions of steel in RCC before and after the yielding of steel differ from those in RC. The tension stiffness developed by the bond action of CFS increases as the amount of CFS increases but that of steel becomes less. With the steel and CFS contributions combined, the tension stiffness of concrete as a whole generally becomes greater than that in RC. There is, however, a case in which tension stiffness of concrete in RCC decreases more than that in RC, because the average bond stress of steel rapidly decreases after the yielding of steel.

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.