Raafat El-Hacha

Near-Surface-Mounted Fiber-Reinforced Polymer Reinforcements for Flexural Strengthening of Concrete Structures

Use of fiber-reinforced polymer (FRP) materials to strengthen bridges has been adopted extensively in the last decade. FRP has been used in different configurations and techniques to use the material effectively and to ensure long service life of the selected system. One of these innovative strengthening techniques is near-surface mounting (NSM) that consists of placing FRP reinforcing bars or strips into grooves precut into the concrete cover in the tension region of the strengthened concrete member. This method is relatively simple and considerably enhances the bond of the mounted FRP reinforcements, thereby using the material more effectively. This paper presents test results of reinforced concrete (RC) T-beams strengthened in flexure with different strengthening systems using FRP reinforcing bars and strips as NSM reinforcement and externally bonded FRP strips. The FRP reinforcements used in this investigation include carbon FRP (CFRP) reinforcing bars and strips and glass FRP (GFRP) thermoplastic strips. Behavior and effectiveness of the materials used for the various strengthening systems are compared. The structural performance and modes of failure of the tested beams are presented and discussed. Test results indicated that using NSM FRP reinforcing bars and strips is practical, significantly improves the stiffness, and increases the flexural capacity of RC beams. The limitations of using NSM FRP reinforcing bars and strips are controlled by serviceability requirements in terms of overall deflections and crack widths rather than delamination, observed by many researchers, of externally bonded FRP reinforcement. Strengthening of RC beams using NSM FRP strips provided higher strength capacity than externally bonded FRP strips using the same material with the same axial stiffness.

Innovative System for Prestressing Fiber-Reinforced Polymer Sheets

Strengthening with bonded prestressed fiber-reinforced polymer (FRP) sheets combines the benefits of excellent durability and structural improvement in terms of serviceability and ultimate conditions. The method offers the benefits of both a prestressed system that contributes to load-carrying capacity before further deformation occurs and a bonded system that sustains a major portion of load under further deformations. This work outlines a strengthening technique that involves prestressing carbon FRP (CFRP) sheets using a new external anchorage system to directly add tension to the sheets by jacking and reacting against the concrete beam itself. Results indicate that the CFRP sheets can be effectively prestressed using the developed anchorage system.

Behavior of Large-Scale Concrete Columns Wrapped with CFRP and SFRP Sheets

AbstractCircumferential wrapping of fiber-reinforced polymer (FRP) sheets is one of the most common applications for repair and rehabilitation of large-scale columns. Common types of fibers used for wrapping are carbon FRP (CFRP), glass FRP (GFRP), and aramid FRP (AFRP). Recently, steel FRP (SFRP) has been introduced as a new class of composites for strengthening applications. Up to now, there has been no experimental data available on the behavior of large-scale columns wrapped with SFRP sheets. Thus, in this paper, the behavior of nonreinforced and reinforced large-scale columns (300×1,200  mm) wrapped with CFRP and SFRP sheets is examined and compared with that of unwrapped columns. The experimental results include stress-strain behavior, ultimate stress, ultimate strain, dilation, and ductility of large-scale columns. This study presents the first ever insight into the strain variation of large-scale circular columns wrapped with CFRP and SFRP sheets using the digital image correlation technique (DICT...

Bond Characteristics of High-Strength Steel Reinforcement

This paper summarizes an investigation undertaken to study the bond characteristics of high-strength steel reinforcement bars commercially known as microcomposite, multistructural, formable steel (MMFX). The objective of the investigation is to examine the applicability of the ACT 318-02 equation and a current proposed equation by Zuo and Darwin on bond behavior of steel reinforcement to the concrete member. The experimental program included two phases. The first phase of the experimental program consisted of testing four beam-end specimens reinforced with MMFX steel bars, whereas the second phase included testing eight beam-splice specimens reinforced with MMFX steel bars. The selected four factors considered in this study were bar size, level of confinement, bonded length, and bar cast position. The bond behavior of the MMFX steel bars was found to be similar to that of conventional Grade 420 MPa (60 ksi) steel up to the proportional limit of 550 MPa (80 ksi). The bond strength of the MMFX significantly changes as the tensile stresses developed in the bar exceed the proportional limit. The test results indicated that both the AC! 318-02 equation and the current proposed equation by Zuo and Darwin on bond are adequate and resulted in conservative prediction at low stress levels up to 550 MPa (80 ksi). At high stress levels, however, the prediction using both equations is unconservative due to the nonlinear behavior of the MMFX stress-strain relationship. Based on the limited number of specimens considered in this study, modification to both the AC1 318-02 equation and the Zuo and Darwin equation is proposed to predict the bond forces beyond the proportional limit for MMFX steel bars.

Effect of Severe Environmental Exposures on CFRP Wrapped Concrete Columns

Deterioration of concrete structures caused by corrosion of reinforcing steel, aging, and weathering is a major problem in harsh environments such as coastal areas and cold regions. In addition, a hot environment, such as in the Arabian Gulf, is recognized as one of the most severe and aggressive environments that affects concrete durability. The purpose of this study is to investigate the effectiveness of strengthening plain concrete cylinders, subjected to extreme temperature variations, by wrapping with two layers of unidirectional carbon fiber-reinforced polymer (CFRP) sheets. Thirty-six plain concrete cylinders ( 150×300 mm ) were tested. Nine specimens served as unstrengthened controls and the remaining cylinders were strengthened with two layers of CFRP sheets. Cylinders were subjected to high temperatures ( 45°C ) , to heating and cooling cycles (23 to 45°C ), and to prolonged heat exposure ( 45°C ) . Some of the cylinders that were subjected to heating and cooling, were later subjected to freezin...

Flexural Strengthening of RC Beams Using Steel Reinforced Polymer (SRP) Composites

Synopsis: This paper presents the application of a new generation of externally bonded composite material in flexural strengthening of reinforced concrete beams. The steel reinforced polymer (SRP) composite consists of high-carbon steel unidirectional Hardwire® fabrics embedded in epoxy resin, and offers high strength and stiffness characteristics at a reasonable cost. In this paper, the mechanical properties of SRP are evaluated and its application in flexural strengthening of RC beams is investigated. Six beams have been tested in three-point bending to study the effect of SRP retrofitting on flexural behavior, failure modes, and crack patterns. Test parameters include variation of the width of SRP sheets and the use of SRP U-wraps at both ends to prevent premature failure caused by delamination of the longitudinal sheet. Significant increase in flexural capacity, up to 53 %, and pseudo-ductile failure modes have been observed in the SRP-strengthened beams. Failure is governed primarily by concrete cover delamination at the tips of the SRP sheets or crushing of concrete at mid-span. It is also shown that the U-wraps have improved flexural stiffness by means of controlling diagonal crack width and providing anchorages to the longitudinal SRP sheets, which reduces their slip. Shear stress concentration near the cut-off point of the SRP sheet has also been investigated. An analytical model is proposed to predict the nominal strength of the SRP-strengthened beams.

Anchorage System to Prestress FRP Laminates for Flexural Strengthening of Steel-Concrete Composite Girders

Using externally bonded (EB) fiber-reinforced polymer (FRP) laminates for strengthening steel-concrete composite girders has recently received more attention from researchers. By prestressing the EB FRP laminates, the material is used more efficiently because a greater portion of its tensile capacity is employed and it contributes to the load-bearing capacity under both service and ultimate conditions. This is an ideal technique because it combines the advantage of using noncorrosive and lightweight advanced composite materials in the form of bonded FRP laminates with the high efficiency offered by external prestressing. An innovative mechanical anchorage system was developed to prestress the FRP laminates directly by jacking and reacting against the steel girder itself. The efficiency of the system was investigated using two types of FRP laminates for flexural strengthening of large-scale steel-concrete composite girders. The used FRP composite materials included carbon-fiber-reinforced polymer (CFRP) plate and steel-fiber-reinforced polymer (SFRP) sheets. The developed anchorage/prestressing system was easy to use/apply and proved to be a feasible and practical system for prestressing both CFRP plate and SFRP sheet. The prestressing levels in the FRP laminates were sufficiently maintained. The prestressing losses were insignificant.

Prestressed and non-prestressed CFRP sheet strengthening: damaged continuous reinforced concrete beams

There is an economy of design inherent in a continuous multiplespan concrete bridge. If one of its spans is severely damaged, there will be a loss in continuity, and the positive bending moments of the remaining spans may become much greater than accounted for in the original design. The remaining spans, even if they carry reduced traffic loads, can deteriorate so severely as to be no longer serviceable. This paper investigates the effectiveness of externally bonded non-prestressed and prestressed carbon fibre reinforced polymer (CFRP) sheets for strengthening the damaged spans of continuous, multiple-span beams. Four two-span, 8.0 m concrete T-beams were constructed and tested. The slenderness of the beams closely approximated that of reinforced concrete bridge girders. All beams were continuous over two equal 4.0 m spans, and were designed to fail in flexure. The beams were damaged by severely damaging one of the two spans, which caused light damage in the second span. One beam was used as an undamaged control, and one beam served as a damaged control. The remaining two beams were damaged and strengthened using external strengthening systems. Both prestressed and non-prestressed CFRP sheets were applied to restore the flexural strength and service load behaviour of the beams. In general, the CFRP sheets effectively restored strength and stiffness to the damaged members.

Modelling of Reinforced Concrete Flexural Members Strengthened with Near-Surface Mounted FRP Reinforcement

Synopsis: This paper presents an analytical investigation conducted to study the flexural behavior of reinforced concrete beams strengthened with various Near-Surface Mounted (NSM) Fiber-Reinforced Polymers (FRP) reinforcements. The materials used in this investigation included carbon-fiber-reinforced-polymer (CFRP) rebars and strips, and glass fiber-reinforced-polymer (GFRP) rebars and strips. The analysis included the effects of strengthening on the serviceability and ultimate limit states as well the effect of tension stiffening. The effectiveness of NSM FRP rebars and strips was examined and compared to externally bonded (EB) FRP strips and sheets using the same material type and axial stiffness. Results from the analytical models were compared with those obtained from experimental studies. The analytical results agree very well with those obtained from the experimental results. It was found that the analytical model could effectively simulate the behaviour of the reinforced concrete beams strengthened with various NSM FRP and EB FRP reinforcements. Using the same axial stiffness of FRP to strengthen reinforced concrete beams, the beams strengthened with NSM FRP reinforcement achieved higher ultimate load than beams strengthened with EB FRP reinforcement. This result is due to the high utilization of the tensile strength of the FRP reinforcement.