Retrofitting of reinforced concrete beams using composite laminates

ABSTRACT

This paper presents the results of an experimental study to investigate the behaviour of structurally damaged full-scale reinforced concrete beams retrofitted with CFRP laminates in shear or in flexure. The main variables considered were the internal reinforcement ratio, position of retrofitting and the length of CFRP. The experimental results, generally, indicate that beams retrofitted in shear and flexure by using CFRP laminates are structurally efficient and are restored to stiffness and strength values nearly equal to or greater than those of the control beams. It was found that the efficiency of the strengthening technique by CFRP in flexure varied depending on the length. The main failure mode in the experimental work was plate debonding in retrofitted beams.

Keywords:

Carbon fibre reinforced plastic (CFRP)

Strengthening

Retrofitting

Laminate

Reinforced concrete beam

Flexure

Debonding

Contents 1. Introduction 2. Materials and methods 2.1. Materials 2.2. Experimental procedure 2.2.1. Manufacture of beams 2.2.2. Testing of control beams 2.2.3. Preloading of beams 2.2.4. Retrofitting of beams 2.2.5. Testing of retrofitted beams 3. Results 3.1. Beams in group RF 3.1.1. Control beams 3.1.2. Retrofitted beams 3.2. Beams in group RS 3.2.1. Control beam 3.2.2. Retrofitted beams 4. Concluding and remarks References

1. Introduction

There are many existing structures, which do not fulfill specified requirements. This may for example be due to upgrading of the design standards, increased loading, corrosion of the reinforcement bars, construction errors or accidents such as earthquakes. To remedy for insufficient capacity the structures need to be replaced or retrofitted.

Different types of strengthening materials are available in the market. Examples of these are ferrocement, steel plates and fibre reinforced polymer (FRP) laminate. Retrofitting of reinforced concrete (RC) structures by bonding external steel and FRP plates or sheets is an effective method for improving structural performance under both service and ultimate load conditions. It is both environmentally and economically preferable to repair or strengthen structures rather than to replace them totally. With the development of structurally effective adhesives, there have been marked increases in strengthening using steel plates and FRP laminates. FRP has become increasingly attractive compared to steel plates due to its advantageous low weight, high stiffness and strength to weight ratio, corrosion resistance, lower maintenance costs and faster installation time.

Earlier research has demonstrated that the addition of carbon fibre reinforced polymer (CFRP) laminate to reinforced concrete beams can increase stiffness and maximum load of the beams. In a study by Toutanj et al. [1] beams retrofitted with CFRP laminates showed an increased maximum load up to 170% as compared to control beams. Another study by Kachlakev and McCurry [2] shows an increase of 150% when beams were strengthened in both flexure and shear with CFRP and glass FRP laminates respectively. Other studies have also been conducted by David et al. [3], Shahawy et al. [4], Khalifa and Nanni [5], Shehata et al. [6], Khalifa et al. [7] in an attempt to quantify the flexural and shear strengthening enhancements offered by the externally bonded CFRP laminates. Ferreira [8] showed that when a...