This chapter discusses the structurally deficient civil engineering infrastructure: concrete, metallic, masonry, and timber structures. The repair of deteriorated, damaged, and substandard civil infrastructure has become one of the important issues for the civil engineer worldwide. The rehabilitation of existing structures is fast growing, especially in developed countries, which completed most of their infrastructure in the middle period of the last century. The structures that were built after World War II had little attention paid to durability issues and the U.S, and Japan had inadequate knowledge of seismic design. The chapter gives an overview of the forms and properties of concrete, metallic, masonry, and timber structures that might need rehabilitation. The ways in which externally bonded FRP can be used to extend the lives of the structures are described. It describes general structural deficiencies and discusses the reasons for using FRP strengthening rather than conventional strengthening techniques.

This chapter discusses the design of externally bonded Fiber-Reinforced Polymer (FRP) strips and plates for shear strengthening of Reinforced Concrete (RC) beams. Flexural and shear failures are the two main failure modes for normal unstrengthened RC beams. Flexural failure is generally preferred to shear failure as the strength-governing failure mode because the former is ductile, which allows stress redistribution and provides warning to occupants while the latter is brittle and catastrophic. Although the flexural failure mode in an RC beam strengthened with FRP in flexure shows much reduced ductility compared to a normal RC beam, it is still a more ductile mode than shear failure. When an RC member is deficient in shear or when its shear capacity is less than the flexural capacity after flexural strengthening, shear strengthening must be considered. It is important to assess the shear capacity of RC beams, which are intended to be strengthened in flexure, and to ensure that the shear capacity exceeds the flexural capacity.

Publisher Summary The durability of externally bonded fiber-reinforced polymer (FRP) composite systems refers to the ability of those materials to provide enhanced structural characteristics to existing structures over timeframes of interest. The durability characteristics of a given FRP composite material applied to a given substrate material is influenced by numerous interrelated factors. This chapter discusses durability issues for generic types of wet-laid and pre-cured thermosetting FRP material systems as well as the interaction between these material systems and four of the most commonly encountered substrates – concrete, wood, masonry, and steel. The durability issues for the types of reinforcements, such as FRP materials bonded into slots cut into a substrate, are expected to overlap with those for internal FRP reinforcements and externally bonded FRP reinforcements. Carefully planned and executed accelerated tests on laboratory specimens can be useful for one-on-one comparisons of various FRP systems applied to a particular type of substrate under a fixed set of testing conditions, although such data might not accurately predict the field performance of the substrate–FRP hybrid system.

Publisher Summary This chapter discusses the design guidelines for Fiber-Reinforced Polymer (FRP)-strengthened Reinforced Concrete (RC) structures. Several documents on the design and construction of externally bonded fiber-reinforced polymer systems for the strengthening of reinforced concrete structures have been published in recent years. The chapter focuses on the design provisions for the flexural and shear strengthening of RC beams and the strengthening/retrofit of RC columns. Both the similarities and the differences between these guidelines are examined. The information presented in the chapter intends to assist the users of the guidelines in interpreting the design provisions contained in them and in looking for the best solutions within the guidelines and beyond. The partial safety factors are intended to account for changes in material properties with time as well as other factors, which is the main reason for the dependency of partial safety factors on fiber types.

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.

Publisher Summary An important application of Fiber-Reinforced Polymer (FRP) composites is to provide confinement to Reinforced Concrete (RC) columns to enhance their load-carrying capacity and ductility. This method of strengthening is based on the phenomenon that the axial compressive strength and ultimate axial compressive strain of concrete can be significantly increased through lateral confinement. Various methods have been used to achieve confinement to columns using FRP composites. In situ FRP wrapping has been the most commonly used technique, in which unidirectional fiber sheets or woven fabric sheets are impregnated with polymeric resins and wrapped around columns in a wet lay-up process, with the main fibers orientated in the hoop direction. In addition, filament winding and prefabricated FRP jackets have also been used. The filament winding technique uses continuous fiber strands instead of sheets/straps, so that winding can be achieved automatically by the means of a computer-controlled winding machine. When prefabricated FRP jackets are used, the jackets are fabricated in half-circles or half rectangles and circles with a slit or in continuous rolls, so that they can be opened up and placed around columns.

Currently, the information regarding the durability and long-term loading characteristics of composite materials used in the construction industry must be obtained from case studies of actual structural systems exposed to their particular environmental conditions. To understand the results of case studies, there must be detailed information on the type of materials used, their manufacturing methods, their strength and stiffness characteristics, the type of environment to which they are exposed, and the length of exposure. This chapter presents the case studies that involve the composites made from carbon fiber, glass fiber, or aramid fiber in a matrix of epoxy or vinylester polymer. Structural members manufactured more than 10 years ago were fabricated using isophthalic polyester resins. Currently, epoxy or vinylester polymers and carbon, aramid or glass fiber materials are invariably used to rehabilitate and to retrofit reinforced, prestressed concrete, metallic systems and timber structures. The chapter discusses the various manufacturing systems that have been used in the case studies.

The use of externally bonded Fiber-Reinforced Polymer (FRP) composite systems for flexural strengthening of structures is the most common application of FRP composites in the civil infrastructure worldwide and has received the greatest amount of research attention. The first uses of externally bonded FRP composite systems for flexural strengthening were on reinforced concrete; however, FRP composites are increasingly being used to strengthen cast iron, modern steel, timber, and masonry in flexure and, in limited cases, wrought iron and riveted steel structures. Most applications of FRP composite systems for flexural strengthening use unstressed FRP plates manufactured in the factory and adhesively bonded to the substrate, mainly due to the relative lack of research and more complicated installation procedure for prestressing technology. This chapter discusses the application of unstressed FRP composite strengthening systems and the current prestressing technology. The chapter focuses on the stages most closely associated with application of FRP strengthening; specification of materials and workmanship, contractor experience, application methods and sequence, site supervision and final inspection, with reference to current guidance and standards. In addition, case studies are used to highlight the practical issues involved in each step.

This chapter discusses the strengthening of metallic structures with fiber-reinforced polymer (FRP) composites. FRP composites can be used to address a variety of structural deficiencies in metallic infrastructure. A superficial comparison of flexural strengthening for metallic and concrete structures suggests many similarities between the design methods; however, virtually every aspect of the design of metallic structures is different in detail. The structural failure modes, critical issues, degradation, and analysis techniques all differ significantly from concrete strengthening. FRP strengthening for metallic structures is a younger technology than for concrete structures and research into the method is still in progress. The chapter focuses on design guidance for strengthening flexural members. It is combined with a description of the current state-of-the-art for other forms of strengthening, advantage could be taken of emerging applications of FRP strengthening to metallic structures. There are two principal stages to designing FRP flexural strengthening for metallic structures. The first of these is a sectional analysis to determine the amount of FRP material needed and the second is a bond analysis to check the capacity of the adhesive joint.