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.

While ductile behavior of a reinforced concrete member can be given by flexural longitudinal steel bars, high strength continuous fibers can contribute as shear and confining reinforcement, which can provide excellent durability as well. Composite R/C members encased by fiber-mesh-mortar tubes seem to be therefore one of the most effective systems. In this research, the following aspects of the system were investigated by experimental studies: (a) Tensile behavior of fiber-mesh-mortar plate—Tensile properties of the fiber-mesh-mortar plates were investigated. The test results showed tension stiffening effect, which reduced crack spacing. (b) Compressive capacities of concrete columns with fiber-mesh-mortar tubes—Uniaxial compressive tests of concrete columns cast in fiber-mesh-mortar permanent forms were conducted. Improvements in strength and ductility were obtained. The confining effect was governed by fiber type, mesh directions and number of mesh layers. (c) Shear and flexural behavior of composite R/C beams encased by fiber-mesh-mortar tube—Composite R/C beams fully encased by fiber-mesh-mortar tubes were tested. The fiber-mesh-mortar tube reduces surface crack spacing on the lateral sides of the beams and improved shear/flexural capacities.

Concrete-filled fiber reinforced polymer (FRP) tubes provide an alternative to conventional reinforced and prestressed concrete columns. The tube helps turn normal strength concrete core into a high performance concrete, i.e., one with high strength, ductility, and durability. The over-reinforcement in concrete-filled tubes helps avoid split rupture of the FRP reinforcement in tension, which is catastrophic in nature. A total of 8 concrete-filled FRP tubes were tested as beam-columns under a combination of axial and flexural loads. The tubes were 9 feet long, and had an outside diameter of 13 11/16 in. with a wall thickness of about 0.55 in.. The study showed that over-reinforced concrete-filled FRP tubes generally behave well as beam columns. They deflect to a lesser extent than the corresponding under-reinforced sections. They are also more efficient than under-reinforced sections, because a smaller portion of their sectional capacity is consumed by secondary moments and P-D effects. Their failure, while in compression, is considered to be gradual and progressive.

In this paper, a new approach predicting the punching shear capacity of FRP reinforced concrete flat slabs without shear reinforcement is introduced in the light of the results of an experimental program conducted at the Centre for Cement and Concrete of the University of Sheffield. The new approach is found to accurately predict the punching shear capacity of the tested slabs. Verification of this new approach is undertaken through comparisons with other test results ensures its validity. Comparisons of the new approach with the ACI 318-95 equation calculating the punching shear capacity of reinforced concrete slabs without shear reinforcement show that the current ACI equation is unconservative in case of FRP reinforcement with low reinforcement ratios. A modification is proposed to the current ACI 318-95 code equation for punching shear in order to accommodate low stiffness FRP reinforcement. Comparisons with test results show that the proposed modification of the ACI code equation leads to good predictions.