Hau Yan Leung

Flexural behaviour of concrete beams internally reinforced with GFRP rods and steel rebars

Use of fibre‐reinforced polymer (FRP) composite rods, in lieu of steel rebars, as the main flexural reinforcements in reinforced concrete (RC) beams have recently been suggested by many researchers. However, the development of FRP RC beam design is still stagnant in the construction industry and this may be attributed to a number of reasons such as the high cost of FRP rods compared to steel rebars and the reduced member ductility due to the brittleness of FRP rods. To resolve these problems, one of the possible methods is to adopt both FRP rods and steel rebars to internally reinforce the concrete members. The effectiveness of this new reinforcing system remains problematic and continued research in this area is needed. An experimental study on the load‐deflection behaviour of concrete beams internally reinforced with glass fibre‐reinforced polymer (GFRP) rods and steel rebars was therefore conducted and some important findings are summarized in this paper.

Uniaxial stress-strain relationship of spirally confined concrete

This paper presents an analytical method of ascertaining the uniaxial stress-strain relationship of spirally confined concrete. Concrete confined by two interlocking spirals is also studied, using a finite element model to determine the magnification factors caused by multiple confinement. Predictions for the behavior of compression specimens with various kinds of reinforcement are given. The paper also presents methods of discerning the behavior of concrete in the compression zone of beams in flexure, which are subjected to strains that vary through the depth.

Compressive Behaviour of Concrete Confined by Aramid Fibre Spirals

Publisher Summary This chapter discusses the experimental results of compressive tests on concrete cylinders wrapped by aramid fiber spirals. The concept of using spiral reinforcement is to restrain the concrete from expansion and thus delay the failure. The increase in ductility and strength are prominent. With the advent of composite materials, replacement of steel by fiber reinforced plastic (FRP) seems to be a rational method to solve the corrosion problems. In addition, due to the difference in the stress–strain behavior of FRP and steel, the induced confining pressure is also different when subjected to compression. The stress of steel remains virtually constant after its yield point so the induced pressure cannot increase after yielding. Both circular concrete cylinders with a single spiral and rectangular concrete specimens with two interlocking spirals are investigated. Concentric compression tests were carried out. It was found that the behavior of confined concrete is influenced not only by the concrete strength but also the spiral leg spacing and the degree of interlocking. Concrete cylinders with close spacing and a high degree of interlocking usually gave higher strength and ductility. Experimental results are compared with analytical data.

Strengthening of RC beams: some experimental findings

This paper aims to study the effect of external glass fibre reinforced polymer (GFRP) plates on the flexural and shear behaviour of structurally deficient reinforced concrete (RC) beams, a total of ten 180mm×250mm×2,500mm beams, including over‐designed, unplated under‐designed and plated under‐designed, were tested under four‐point bending condition. Experimental results indicate that the use of GFRP plates enhances the strength and deformation capacity of RC beams by altering their failure modes. Application of side plates on shear‐deficient RC beams appears to be more effective than using bottom plates on flexure‐deficient RC beams. However, without any improvement of concrete compressive capacity, additional shear capacities provided to the beams under the action of side plates increase the likelihood of beam failure by concrete crushing. Simultaneous use of bottom and side plates on flexural‐ and shear‐deficient RC beams may result in reduced deflection.

Fibre reinforced polymer materials for prestressed concrete structures

Fibre reinforced polymer (FRP) materials are currently used for concrete structures in areas where corrosion problems are serious. Recent applications of FRP rebars in normal reinforced concrete structures in fact cannot fully utilise the strength of FRP. A more rational use of FRP would be in the area of prestressed concrete (PC) structures. In spite of the superb strength provision of FRP tendons over steel tendons, use of FRP PC members is often questioned by practising design engineers. This is largely due to the brittleness of FRP tendons and lack of ductility in FRP RC structures. Recent research has demonstrated some important findings in promoting the confidence of adopting FRP RC beams. This paper reviews some recent work on the use of FRP in PC structures. Future possible research areas are also highlighted.

Flexural Performance of Concrete Beam Splices with Different Surrounding Concretes

In this study, tests were conducted to investigate the effect of different concretes on the behaviour of reinforced concrete beams with central splices. Five beam specimens were prepared using different concrete mixes in their splice regions. Experimental results indicated that the bond failure of the spliced rebars governed the ultimate flexural behaviour of all specimens, except the one cast with steel fibres. A small increase in flexural strength was found for both the spliced beams cast with high‐strength concrete and steel fibres. Moreover, use of high‐strength concrete and steel fibrous concrete led to a remarkable improvement in the beams displacement capacity. The effect of pulverised fuel ash on the splice performance was insignificant while the introduction of silica fume caused improvements in loading capacity and ductility.

Analysis of FRP-Reinforced Concrete Beam with Aramid Spirals as Compression Confinement

Publisher Summary This chapter presents a method of analysis for the response of concrete beams reinforced with fiber-reinforced-plastic (FRP) tension rods and aramid spirals. FRPs are largely noncorrodable, light in weight, and high in strength and are attractive as replacements for steel in reinforced concrete. Depending on the quantities of compression confinement and longitudinal reinforcement, failure may occur either in the compression region or the tensile bars. However, because FRPs exhibit linear elastic behavior, it is desirable that concrete crushing controls the failure of flexural concrete members. Such behavior can be enhanced by the use of compression confinement, which significantly enhances the ultimate strain in compression. Three different kinds of longitudinal reinforcement are adopted; carbon fiber reinforced polymer, AFRP, and GFRP. Both under-reinforced and over-reinforced sections are described in the chapter. It is found that the ratio of neutral axis depth and effective depth can be used as an indicator for FRP-reinforced beam with aramid spirals. Based on the computer solutions, a simple design chart is also proposed in the chapter.

Test on Prestressed Concrete Beam with AFRP Spiral Confinement and External Aramid Tendons

An experimental study of a new form of prestressed concrete beam is described in this paper. The paper shows how Aramid Fiber Reinforced Polymers (AFRPs) are used to provide compression confinement in the form of interlocking circular spirals, while external tendons are made from parallel-lay aramid ropes. The response shows that the confinement of the compression flange significantly increases the ductility of the beam, allowing much better utilization of the fiber strength. The failure of the beam is characterized by rupture of spiral confinement reinforcement.