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.

Wrapping of columns by means of FRP (fiber reinforced polymer) reinforcement enhances the structural behaviour of concrete columns considerably. At the Magnel Laboratory for Concrete Research a test programme is set-up to evaluate some specific problems in the modelling of FRP confined concrete, i.e. effective circumferential FRP failure strain and effect of increasing confining action. Parameters studied are FRP type, bonded or unbonded wrapping application, column shape and strengthening lay-out. Both wrapped cylinders and wrapped columns are investigated. An analytical verification of the test results is performed according to different models. From the test results obtained so far, the efficiency of this strengthening technique has been demonstrated, both in terms of structural performance and ease-of-application. Quality of the application (voids, protrusions, etc.) and the wrapping concept (bonded or unbonded, partial wrapping, etc.) influence the strengthening effect.

In the aftermath of the 1995 Hyogo-Ken Nanbu Earthquake in which many severe failures of bridge piers occurred, numerous studies have been conducted on ways to retrofit existing RC columns and piers. As a result of this research, it has been found that continuous fiber sheet offers a feasible means of retrofitting. Consequently, several design guidelines on the use of FRP sheets for retrofitting highway, railway and subway structures have been proposed in recent years. The JSCE (Japan Society for Civil Engineers) Concrete Committee on FRP Sheet, which was setup in 1998, has been commissioned to establish a new design method for seismic retrofit of bridge columns and piers. It seeks to unify all the existing guidelines on a performance-based design concept. This paper describes mainly the new design method of shear strength and ductility of retrofitted RC structures using FRP sheet. Design equations for shear strength and ductility are also presented.

Prevalently compressed concrete columns can be transversely confined in order to obtain increase in strength and ductility. Generally, two principal methodologies of advanced confinement are used: the “Wrapping” technique which consists of wrapped concrete columns using thin carbon or glass flexible straps epoxy-bonded concrete surface; and concrete filled FRP tubes (CFFT) in which the tube is the pour form, protective jacket, confining mechanism, and shear and flexural reinforcement. The purpose of this paper is to theoretically model the stress-strain behavior of concrete confined by FRP straps or tubes, evidencing the straight dependence of s - e curve on the hoop mechanical properties of the transverse composite reinforcement. The proposed model consists of a generalization of the theory of elasticity, i.e. a step by step application of Navier classical relations which define the stress-strain laws in states of triaxial stress. The theoretical results are compared with experimental compression tests carried out on ten cylindrical concrete specimens confined with two different typologies of fiber composite tubes.