Omar Chaallal

Flexural response of concrete beams reinforced with FRP reinforcing bars

The authors conducted an experimental and theoretical comparison between flexural behaviors of concrete beams reinforced with fiber reinforced plastic (FRP) reinforcing bars and identical conventionally reinforced ones. Comparisons were made in relation to cracking behavior, load-carrying capacities and modes of failure, load-deflection response, flexural rigidity, and strain distribution. The results revealed that perfect bond exists between FRP reinforcing bars and the surrounding concrete. Also, American Concrete Institute (ACI) Code formulas for predicting deflection response, cracking-ultimate moments, and cracked-effective moments of inertia can easily be adapted for modeling the flexural behavior of concrete beams reinforced with FRP reinforcing bars if appropriate modifications are made.

Shear strengthening reinforced concrete beams with fiber-reinforced polymer: Assessment of influencing parameters and required research

This paper focuses on shear strengthening of reinforced concrete (RC) beams with externally bonded fiber-reinforced polymer (FRP) composites. Its aims are to synthesize findings of the research studies conducted to date, and to examine and analyze the parameters that have the greatest influence on the shear behavior of RC members strengthened with externally bonded FRP. Over 100 tests were considered in the synthesis. Several conclusions were drawn from this work and are discussed. It was found that the parameters related to the properties of the FRP and to those of the shear steel reinforcement are not the only ones having an influence on the shear behavior of RC members strengthened with externally bonded FRP. The shear span ratio a/d, longitudinal steel reinforcement ratio, and geometry of the member also have influence on the shear behavior of these members and deserve further investigation. An experimental parametric study with close variable control is recommended.

BOND STRENGTH AND LOAD DISTRIBUTION OF COMPOSITE GFRP REINFORCING BARS IN CONCRETE

The objective of this investigation was to examine the bond strength of glass fiber reinforced plastic (GFRP) reinforcing bars in concrete. Twenty concrete beams reinforced with four nominal diameters from 12.7 to 25.4 mm of GFRP and steel reinforcing bars were tested to determine the bond strength of GFRP reinforcing bars in comparison with steel reinforcing bars. Additionally, the distribution of tensile and bond stresses along the embedment length of GFRP reinforcing bars was studied by five pullout tests using instrumented 19.1-mm-diameter GFRP reinforcing bars compared with steel reinforcing bars in concrete. Only one type of GFRP reinforcing bar was used in this study. Test results reveal that the diameter effect on bond observed for steel reinforcing bars is also present for GFRP reinforcing bars. The bond strength of GFRP bars is lower than that of steel reinforcing bars. The bond strength from beam tests is lower than that from pullout tests. Furthermore, it was found that the distribution of bond stress along the embedment length of GFRP reinforcing bars is nonlinear.

PERFORMANCE OF REINFORCED CONCRETE T-GIRDERS STRENGTHENED IN SHEAR WITH CARBON FIBER-REINFORCED POLYMER FABRIC

Results are presented from an experimental investigation into the performance of 20-ft-long reinforced concrete (RC) T-girders strengthened in shear using epoxy-bonded bidirectional carbon fiber reinforced polymer (CFRP) fabric. The aim was to evaluate and gain insight into the effectiveness of shear strengthening of large-scale girders with externally bonded CFRP under a low shear span condition. Four series of tests, corresponding to stirrup spacings of 5.5, 8, 16, and 24 in, were considered. Each series of girders included control specimens with no CFRP wrap and specimens retrofitted in shear with 1, 2, and 3 layers of CFRP wrap. Results indicate that for unwrapped specimens, values for nominal shear predicted by ACI underestimated, by 40-80%, the shear resistance of beams developing arch action, such as those considered herein. For wrapped specimens, the maximum shear force as well as the midspan deflection generally increased with the number of CFRP layers. The optimum number of layers to achieve the maximum gain in shear resistance was found to depend on the internal shear steel reinforcement provided. The effective CFRP strain used to calculate the contribution of the CFRP to the shear capacity was correlated to the total shear reinforcement ratio consisting of steel stirrups and CFRP wrap. Retrofitting RC girders in shear with CFRP wrap also increased the ductility. Experimental evidence shows an optimum combination of CFRP layers and steel stirrups exists for a maximum increase in ductility.

Behavior of reinforced concrete T-beams strengthened in shear with carbon fiber-reinforced polymer : An experimental study

The results of an extensive experimental investigation on reinforced concrete T-beams retrofitted in shear with externally bonded carbon fiber-reinforced polymer (CFRP) are presented. The authors researched the CFRP ratio, the internal shear steel reinforcement ratio and the shear length to the beams depth ratio. By studying the aforementioned parameters, the behavior of reinforced concrete T-beams strengthened in shear with externally applied CFRP was analyzed. It appears that the contribution of CFRP to shear resistance depends on if a strengthened beam is reinforced in shear with internal transverse steel reinforcement, and not on the CFRP stiffness provided. It seems that the American Concrete Institute and the Canadian Standards Association guidelines fail to incorporate the presence of the transverse resistance and overestimates the shear resistance for high fiber reinforced polymer thickness.

PERFORMANCE OF FIBER-REINFORCED POLYMER-WRAPPED REINFORCED CONCRETE COLUMN UNDER COMBINED AXIAL-FLEXURAL LOADING

Many countries around the world have the tremendous need to repair and strengthen their existing infrastructure. This paper presents results of an experimental investigation into the performance of reinforced concrete beam-columns strengthened with externally applied bidirectional carbon fiber-reinforced polymer (CFRP) material. The external moment was applied to the specimens through corbels that were part of the columns. The overall length of the column specimens, including the corbels, was 11.8 ft (3.6 m). Six series of tests were performed on the specimens. The first five series, corresponding respectively to eccentricities of 0, 3, 6, 12, and 16 in. (0, 75, 150, 300, and 400 mm), were performed under a combined axial-flexural loading condition. The sixth series was tested in four-point pure flexure with no axial load. Results indicate that the strength capacity of beam-columns improved significantly as a result of the combined action of the longitudinal and the transverse weaves of the bidirectional composite fabric. The longitudinal CFRP elements contributed mostly to flexural capacity, whereas the transverse elements enhanced the compressive capacity of the compression zone through confinement action. The maximum capacity gain achieved was slightly below 30% in pure compression, and over 54% in pure flexure. Under combined axial force-bending moment conditions, the gain in moment capacity attained 70%. The increase in the compressive strain attributed to the confinement effect varied from 49% to 166%. The transverse confinement was engaged in the compression zone from the early stage of loading. Finally, within the conditions and the limits of this study, the proposed design procedure, based on the stress of confined concrete in the compression zone in conjunction with an effective confinement ratio that takes into account the rectangular shape of the beam-columns, compared reasonably well with experimental results.

Glass fibre reinforced plastic (GFRP) rebars for concrete structures

Abstract The study described is a part of a large-scale experimental and theoretical programme on the application of fibre reinforced plastic ( frp ) reinforcement for concrete structures initiated at the Universite de Sherbrooke (Sherbrooke, Canada). The programme is being carried out to gain an insight into the flexural behaviour of concrete beams reinforced with glass fibre reinforced plastic ( gfrp ) rebars. Results of experimental study on 3.3 m long beams reinforced with two different types of gfrp rebars are presented and compared to that of conventional steel reinforced concrete beams. Three series of reinforced concrete beams were tested in flexure. The beams were 200 mm wide and respectively 300, 450 and 550 mm high. The paper also attempts to present the properties of gfrp and its components and to give an oversight of relevant research activities involving gfrp rebars as reinforcement for concrete units.

Influence of Coarse Aggregate on Elastic Properties of High-Performance Concrete

The paper resports tests carried out on high-strength concrete made with differnt types of crushed rocks. These tests highlight the role played by coarse-aggregate through the elastic properties of the parent rock. The results obtained open an opportunity to review the present formulas relating E sub c to F sub c recommended by some codes.

CONFINEMENT MODEL FOR AXIALLY LOADED SHORT RECTANGULAR COLUMNS STRENGTHENED WITH FIBER-REINFORCED POLYMER WRAPPING

A confinement model, describing the behavior of rectangular concrete columns retrofitted with externally bonded fiber-reinforced polymer (FRP) material and subjected to axial stress, is presented. The derivation of the proposed model is based on the findings of an extensive experimental investigation involving the testing of 90 rectangular specimens representing 3 cross-sectional aspect ratios, 2 concrete strengths, and 5 different numbers of FRP layers. The proposed model is trilinear, both in the axial and lateral directions, and captures the key parameter observed; namely, the ratio of the stiffness of the FRP jacket in the lateral direction to the axial stiffness of the column. The proposed model was found to fairly accurately describe results reported in other similar research studies.

Shear Strengthening of RC Beams with EB FRP: Influencing Factors and Conceptual Debonding Model

This paper deals with the shear strengthening of RC beams using externally bonded (EB) fiber-reinforced polymers (FRP). Current code provisions and design guidelines related to shear strengthening of RC beams with FRP are discussed in this paper. The findings of research studies, including recent work, have been collected and analyzed. The parameters that have the greatest influence on the shear behavior of RC members strengthened with EB FRP and the role of these parameters in current design codes are reviewed. This study reveals that the effect of transverse steel on the shear contribution of FRP is important and yet is not considered by any existing codes or guidelines. Therefore, a new design method is proposed to consider the effect of transverse steel in addition to other influencing factors on the shear contribution of FRP ( Vf ) . Separate design equations are proposed for U-wrap and side-bonded FRP configurations. The accuracy of the proposed equations has been verified by predicting the shear st...