![]()
This textbook deals with the theory and design of structural components and systems made of fiber-reinforced polymer (FRP) composites. The primary focus of this chapter is on the design of multifunctional structures that are commonly encountered in civil and military infrastructure.
FRP composites are made of two or more constituent materials (fibers, resins, fillers, and additives) with different physical and chemical properties. These constituents retain their identity in a finished composite product without blending fully or even losing their microstructural characteristics. The finished product (composite) exhibits superior thermomechanical performance over its constituents. For example, fibers are weak in compression and do not transfer shear from one fiber to another, while the binder (polymer resin) after curing (commonly known as matrix) provides the shear transfer capability and compressive strength; together they form a composite that is made of glass, carbon, or other fibers or fabrics with polymeric resin, such as epoxy or polyurethane. Composites are tailor-made with different fibers (glass, carbon, aramid, or plant-based) providing strength and stiffness, while the polymer matrix provides force transfer between fibers. The idea of such juxtaposition is to enhance strength, durability, cost-effectiveness, or other features. Furthermore, the matrix protects the fiber from environmental degradation and helps in efficiently manufacturing a product on a high-volume basis.
Polymer composites are identified by a specific fiber. For example, composites with glass or carbon fibers are referred to as glass FRP composites or carbon fiber-reinforced composites, respectively. In addition, composite manufacturers and users refer to these products as fiber-reinforced composites (FRP), glass-reinforced plastics (GRP), and polymer matrix composites (PMC). Though several examples of composites occur in nature, the modern synthetic composite field implementation only began in the late 1940s with the advent of quality glass reinforcements and room-temperature-cured resins. Although Leo Hendrik Baekeland invented modern composites with synthetic resins in the early 1900s, composites have been successfully utilized in a diverse range of applications, only after World War II.
In recent years, several large-scale FRP composite structures have been erected to demonstrate the potential of composites in major civil engineering applications. These include a 112 m pedestrian bridge in Scotland (Head, 1994), a 38 m pedestrian bridge in Denmark (McManus, 1997), and several highway bridges in the USA (GangaRao et al., 1999). Yet, despite the strong indications of the potential of these materials, FRP composites continue to be slow in penetrating the mainstream civil engineering marketplace. One of the reasons for this continued lack of market penetration and growth has been that civil engineers have not possessed the technical information and design tools necessary to exploit composite materials cost-effectively.
This textbook addresses the need for an improved understanding of composite materials and their behavior and design within an infrastructure system context. The broad aim is to improve the fundamental understanding of composite material and system response from a structural engineering perspective. It also aims to assist in the development of a more complete understanding of the constituent materials for fiber composite structural elements and how their behavior influences the overall behavior of such elements, especially when they are assembled. The first half of this book covers engineering properties of the constituent materials (fiber and matrix), mechanics and analyses of composite lamina and components, and consideration of hygrothermal and other environmental effects. The second half then covers the design philosophy for composite members under different loading actions, including the design of composite members, connections and structural systems. The Appendices provide supporting information and theories behind the mechanics and design of fiber composites.
1.1 Historic Perspective
FRP composites are composed of at least two constituent materials (e.g., glass or carbon fibers combined with resins like epoxy or polyester) differing in terms of thermomechanical properties. However, the idea is to engineer the combined properties to be superior to the constituent materials. The constituent materials remain separate and distinct in a composite, that is, the fiber reinforcement remains distinct from the matrix, which is the cured resin. The resins help bond together fibers, fabrics, or fibrous particulates. The resins primarily dictate the manufacturing process and processing conditions. They partially protect fibers and fabrics from environmental damage such as chemical or thermal exposure. In short, fibers and resins contribute their strengths (i.e., fibers with maximum tension or bending strengths while resin providing shear transfer) to “tailor-make” the end product with a specific use in mind, i.e., optimal strength, stiffness, or durability.
The history of FRP composites can be traced back to Mesopotamia (present-day Iraq). The Mesopotamians used mud and straw in bricks and bonded copper sheets with natural resins. In addition, decorative pieces made of cloisonnes (a kind of enamel) were produced in Asia and Europe. All the items were made with at least two distinctly different materials combined into one final product of improved performance. Organic polymers from tree and plant secretions, fossilized resins, and those from fish and animal offal were in practice, also. Furthermore, cotton, wool, and linen are natural organic fibers that have been decorated with fine gold threads as a part of earlier (old) composites. The inclusions of metallic wires to reinforce nonmetallic applications are many. For example, decorative organic plastic and paper pulp were used to make canes and umbrella handles in the late nineteenth century in Europe (Seymour and Deanin, 1986), as nonstructural composites.
Sophisticated applications of composites have been identified in nature from time immemorial, and man-made composite applications such as straw-reinforced adobe or brick in Tulou houses (Figure 1.1a) (Liang et al., 2011) and beehives (Figure 1.1b) (Chernick, 2009) have been cited in the literature. Typical beehive houses of a high-domed structure with adobe brick were found to be extremely durable with significant heat resistance due to favorable thermal properties f...
