Hollaway / Teng Strengthening and Rehabilitation of Civil Infrastructures Using Fibre-Reinforced Polymer (FRP) Composites

1. Auflage 2008
ISBN: 978-1-84569-489-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 416 Seiten

Reihe: Woodhead Publishing Series in Civil and Structural Engineering

The repair of deteriorated, damaged and substandard civil infrastructures has become one of the most important issues for the civil engineer worldwide. This important book discusses the use of externally-bonded fibre-reinforced polymer (FRP) composites to strengthen, rehabilitate and retrofit civil engineering structures, covering such aspects as material behaviour, structural design and quality assurance.The first three chapters of the book review structurally-deficient civil engineering infrastructure, including concrete, metallic, masonry and timber structures. FRP composites used in rehabilitation and surface preparation of the component materials are also reviewed. The next four chapters deal with the design of FRP systems for the flexural and shear strengthening of reinforced concrete (RC) beams and the strengthening of RC columns. The following two chapters examine the strengthening of metallic and masonry structures with FRP composites. The last four chapters of the book are devoted to practical considerations in the flexural strengthening of beams with unstressed and prestressed FRP plates, durability of externally bonded FRP composite systems, quality assurance and control, maintenance, repair, and case studies.With its distinguished editors and international team of contributors, Strengthening and rehabilitation of civil infrastructures using fibre-reinforced polymer (FRP) composites is a valuable reference guide for engineers, scientists and technical personnel in civil and structural engineering working on the rehabilitation and strengthening of the civil infrastructure. - Reviews the use of fibre-reinforced polymer (FRP) composites in structurally damaged and sub-standard civil engineering structures - Examines the role and benefits of fibre-reinforced polymer (FRP) composites in different types of structures such as masonry and metallic strengthening - Covers practical considerations including material behaviour, structural design and quality assurance

Autoren/Hrsg.

Hollaway, L C

Teng, J G

Leseproben

2 Fibre-reinforced polymer (FRP) composites used in rehabilitation
L.C. HOLLAWAY,     University of Surrey, UK Publisher Summary
This chapter provides an introduction to the Advanced Polymer Composite (APC) materials used in the rehabilitation of Reinforced Concrete (RC), Prestressed Concrete (PC) and metallic and masonry structures. The type of upgrading considered is that required for flexural and shear resistance of beams and wrapping of RC columns. The chapter discusses the mechanical and in-service properties of the two major components of the composite and the properties are considered in terms of Fiber-Reinforced Polymer (FRP) composites used in construction and exposed to various civil engineering environments. As the composite plate or the FRP composite wraps used in the rehabilitation of structures are fabricated from the same materials and manufactured by the same techniques as those for the FRP civil engineering structural materials, their mechanical and in-service properties would be of similar values. The chapter discusses some aspects of bonding composites to the more conventional civil engineering materials. 2.1 Introduction
This chapter provides an introduction to the advanced polymer composite (APC) materials used in the rehabilitation of reinforced concrete (RC), prestressed concrete (PC) and metallic and masonry structures. The type of upgrading considered is that required for flexural and shear resistance of beams and wrapping of RC columns. The chapter will discuss separately the mechanical and in-service properties of the two major components of the composite (viz. the polymer matrix and the fibre) and will continue by considering these properties in terms of fibre-reinforced polymer (FRP) composites used in construction and exposed to various civil engineering environments. As the composite plate or the FRP composite wraps used in the rehabilitation of structures are fabricated from the same materials and manufactured by the same techniques as those for the FRP civil engineering structural materials, their mechanical and in-service properties will be of similar values. APC materials consist of strong stiff fibres in a polymer matrix and require scientific understanding from which design procedures may be developed. The mechanical and physical properties of the composite are controlled by the constituent properties and by the microstructural configurations. The matrix must bond well with the fibre surface to enable transfer of stresses efficiently between the fibres. Fibre alignment, fibre content and the strength of the fibre–matrix interface all influence the performance of the composite. Furthermore, highly specialised processing techniques are used which take account of the handling characteristics particularly of carbon fibres, a material now commonly used to upgrade or strengthen structural systems. The materials used for composite plate bonding of beams or the wrapping of columns could be fabricated by a number of techniques, but two methods are mainly used; these are the pultrusion and the pre-impregnated fibre in a resin (prepreg). This latter method can be a factory-made preformed plate or an uncured prepreg used in conjunction with a film adhesive. Both components are wrapped around the structural member on site and then fully cured under pressure and elevated temperature in one operation. The advantage of utilising the latter method over that of the two former methods is that the structural member can be of any geometrical shape. In certain circumstances, other systems have been used; these include: (i) the wet lay-up system for plate bonding or column wrapping, (ii) the resin transfer moulding (RTM) systems or variations of these, mainly for plate bonding, such as resin infusion under flexible tooling (RIFT), (iii) the XXsys Technologies (which is used only for specialised work) or variations of this method, mainly for column wrapping. In the above three processing methods, the polymer of the composite also acts as the adhesive between the composite and the structural members; they have been fully described in Hollaway and Head (2001). The successful strengthening of structural members with FRP materials is dependent upon the quality and integrity of the composite adherent, the effectiveness of the adhesive used and the surface preparation of the two adherents to be joined. The basic requirements for the creation of a satisfactory bonded joint are: • selection of a suitable adhesive; • adequate preparation of the adhesive surface; • appropriate design of the joint; • controlled fabrication of the joint; • a post-bonding quality assurance. This chapter will discuss some aspects of bonding composites to the more conventional civil engineering materials. The long-term durability of FRP composite materials for rehabilitation of structural systems is often quoted as the main reason for utilising the material. However, the durability of the composite material is highly dependent upon the choice of the constituent materials, the methods of their fabrication and the environment into which they are placed throughout their lives. Although FRP composite materials do not corrode they do undergo chemical and physical changes over a period of time. In addition, the durability of adhesives may be affected by the environment into which they are placed. The chemical degradation of the matrix component of the composite, of the adhesive, of the substrate and of chemical bonds across the interface as a result of interaction with water and other chemicals are all possible; however, the matrix component and the structural adhesives are selected with essentially hydrolysis-resistant chemistry and so chemical attack is not generally an important degradation mechanism. Any significant weakening of adhesive joints as a result of swelling would be associated with the absorption of large amounts of water, and such materials are considered unsuitable for structural applications. However, the rehabilitation of structures is not generally associated with immersion in water or chemicals, but there may be occasions on which a high humidity associated with the construction exists. If these conditions do exist the resin manufacturer should be consulted. This chapter will detail the materials that are used for the upgrading of structures and will address the issues raised in this introduction. It will show that advanced polymer composites utilised in the rehabilitation of structural members can provide long lifetimes with very little maintenance. 2.2 Component parts of composite materials
The advanced polymer composite essentially consists of two component materials: (i) the matrix material or polymer, which is generally the low-strength and low-modulus component and (ii) the fibre, which is the relatively high-strength and high-modulus component. Under stress, the fibre utilises the plastic flow of the matrix to transfer the load to the fibre; this results in a high-strength and high-modulus composite. The primary phase, the fibres of high aspect ratio, must be well dispersed and bonded into the secondary phase, the matrix. The principal constituents of the composite are, therefore, the fibre, the matrix and the interface. This last component is an anisotropic transition region with a graduation of properties. The interface is required to provide adequate chemical and physical bonding stability between the fibre and the matrix in order to maximise the coupling between the two phases and thus allow stresses to be dispersed through the matrix, and thus transferred to the reinforcement. By wetting the reinforcement with the matrix in the liquid or low-viscosity state, coupling between the two components is provided. In the plate bonding technique, the fibre array is invariably aligned along the longitudinal direction of the beam or aligned transversely around the column. Consequently, the main function of the matrix is to combine and to protect the fibre against the external environment into which the composite will be placed. The two component parts of the polymer composite will now be discussed. 2.3 Properties of matrices
The polymer is an organic material composed of molecules made from many repeats of the same simpler unit called the monomer. There are many different polymer matrices used in advanced polymer composites but, within the composite family, there are two major types, the thermosetting and the thermoplastic binders. The thermoplastic polymer is not used as the matrix material for the rehabilitation of structural members, but the thermoplastic polyacrylic fibre, which is formed from the thermoplastic polymer, polyacrylonitrile, is used as the PAN precursor for the manufacture of high-strength and high-modulus carbon fibre (see Section 2.4). Further information on the thermoplastic polymer may be obtained from Hollaway and Head (2001). The thermosetting polymers are those which form the matrix material of the composite used in the rehabilitation of structures. They are manufactured from liquid or semi-solid precursors, which harden irreversibly. On completion of the chemical reaction, the liquid resin is converted to a hard solid by...