Fiber-Reinforced Composite Material (FRP)

Fiber-Reinforced Composite Material (FRP), also known as Fiber Reinforced Polymer/Plastics, consists of fiber materials and matrix materials. When used in building structures, commonly used fiber materials are carbon fiber and glass fiber, while matrix materials include epoxy resin, vinyl ester resin, and unsaturated polyester resin. From micro to macro scale, extremely fine fiber filaments are first arranged or woven in specific directions into forms such as plates or fabrics, then bonded with matrix materials to form FRP products.

Features of FRP

(1)Lightweight

The density of FRP is approximately 14–21 kN/m³, about 1/6–1/4 that of steel, and lighter than aluminum. When used in large-span structures, it significantly reduces the dead weight of the structure.

Taking the Jobs Theater as an example, the entire carbon fiber roof weighs only 80 tonnes and can be installed through integral hoisting. With a roof diameter of approximately 47 m, the average weight per square meter is 46 kg, equivalent to only a 6 mm thick steel plate. This remarkable weight reduction makes it possible for the roof to support the surrounding structural glass, creating an amazing spatial effect.

(2)High Strength

Natural materials have defects in their crystal structure. The finer the material, the fewer defects and the higher the strength. Carbon fiber and glass fiber can achieve strengths 10–20 times that of steel. Considering the strength difference between fiber and matrix, the strength-to-weight ratio of FRP material can typically reach more than 4 times that of steel, enabling FRP large-span structures to achieve spans 2–3 times larger than traditional structures. Some researchers have demonstrated that Carbon Fiber Reinforced Polymer (CFRP) cables could be used to construct the Gibraltar Bridge with a span of 10,000 m, illustrating its remarkable strength.

(3)Easy Molding

The production process of FRP includes pultrusion, winding, hand lay-up, injection molding, and other methods. Not only can FRP products with regular shapes be mass-produced, but plates of almost any shape can be manufactured to create nonlinear architectural forms.

(4)Easy to Disassemble and Assemble

FRP offers various connection methods, including bolting, and its lightweight nature makes disassembly and assembly easier. Zaha Hadid's Chanel Mobile Art Museum, covering an area of approximately 700 m², features main structural components made of steel and an outer skin of Glass Fiber Reinforced Polymer (GFRP) curved panels no wider than 2.55 m. It can be dismantled and assembled in a short time, enabling successful global tours from Hong Kong to Tokyo, New York, Moscow, London, and Paris.

(5)Corrosion Resistance

What is the biggest concern when building by the sea? It's corrosion, which affects both steel and concrete structures. FRP can be used long-term in acidic, alkaline, saline, and humid environments, and can also resist corrosion from de-icing salts and airborne salt.

(6)Anisotropy

Unlike isotropic materials such as steel and aluminum, FRP exhibits significantly different mechanical properties along and perpendicular to the fiber direction due to directional fiber arrangement (unidirectional or bidirectional weaving). This characteristic falls within the realm of composite material mechanics, making mechanical analysis complex and design challenging. Due to low interlayer tensile/shear strength, connection points can become structural weak points, necessitating minimal connections and careful connection design. Steel nodes can be used for critical connection points.

Other Characteristics of FRP

Elastic Modulus

The elastic modulus of FRP is comparable to that of concrete and wood. Despite its high strength, structural design is often controlled by deformation. Deformation can be managed through appropriate structural form selection, combination with other materials, and prestressing applications.

Linear Expansion Coefficient

The coefficient is significantly lower than that of metallic materials such as steel and aluminum. This results in minimal temperature stress in ultra-long structures, facilitating structural design, while also providing excellent thermal insulation without requiring additional building insulation layers, saving building space.

Fire Resistance

Resin mechanical properties decrease at high temperatures due to softening. Fire resistance can be improved by incorporating flame retardants into the resin and applying surface fire protection treatments. Well-treated FRP can achieve fire resistance comparable to concrete.

Economic Efficiency

While FRP materials are more expensive than steel, their overall cost-effectiveness is competitive when considering their lightweight nature, high strength, corrosion resistance, and low maintenance requirements. Technological advances continue to reduce production.