Fibre Reinforced Polymer (FRP) Composites
The Evolution of Composites within Civil Engineering
For years, civil engineers have been in search for alternatives to steels and alloys
to combat the high costs of repair and maintenance of structures damaged by corrosion and heavy use. For example, cost estimates
for maintenance of highway bridge decks composed of steel-reinforced concrete are up to $90 billion/year. Since the 1940s,
composite materials, formed by the combination of two or more distinct materials in a microscopic scale, have gained increasing
popularity in the engineering field. Fiber Reinforced Polymer (FRP) is a relatively new class of composite material manufactured
from fibers and resins (Figure 1) and has proven efficient and economical for the development and repair of new and deteriorating
structures in civil engineering. The mechanical properties of FRPs make them ideal for widespread applications in construction
FRP Laminate Structure
FRPs are typically organized in a laminate structure, such that each lamina (or flat layer)
contains an arrangement of unidirectional fibres or woven fibre fabrics embedded within a thin layer of light polymer matrix
material (Figure 2). The fibres, typically composed of carbon or glass, provide the strength and stiffness. The matrix, commonly
made of polyester, Epoxy or Nylon, binds and protects the fibers from damage, and transfers the stresses between fibers.
Suitability of FRP for Uses in Structural Engineering
The strength properties of FRPs collectively make up one of the primary reasons for which
civil engineers select them in the design of structures. A material's strength is governed by its ability to sustain a load
without excessive deformation or failure. When an FRP specimen is tested in axial tension, the applied force per unit cross-sectional
area (stress) is proportional to the ratio of change in a specimen's length to its original length (strain). When the applied
load is removed, FRP returns to its original shape or length. In other words, FRP responds linear-elastically to axial stress.
The response of FRP to axial compression is reliant on the relative proportion in volume of fibers, the properties
of the fiber and resin, and the interface bond strength. FRP composite compression failure occurs when the fibers exhibit
extreme (often sudden and dramatic) lateral or sides-way deflection called fiber buckling.
FRP's response to transverse
tensile stress is very much dependent on the properties of the fiber and matrix, the interaction between the fiber and matrix,
and the strength of the fiber-matrix interface. Generally, however, tensile strength in this direction is very poor.
stress is induced in the plane of an area when external loads tend to cause two segments of a body to slide over one another.
The shear strength of FRP is difficult to quantify. Generally, failure will occur within the matrix material parallel to the
Among FRP's high strength properties, the most relevant features include excellent durability and corrosion
resistance. Furthermore, their high strength-to-weight ratio is of significant benefit; a member composed of FRP can support
larger live loads since its dead weight does not contribute significantly to the loads that it must bear. Other features include
ease of installation, versatility, anti-seismic behaviour, electromagnetic neutrality, excellent fatigue behaviour, and fire
However, like most structural materials, FRPs have a few drawbacks that would create some hesitancy in
civil engineers to use it for all applications: high cost, brittle behaviour, susceptibility to deformation under long-term
loads, UV degradation, photo-degradation (from exposure to light), temperature and moisture effects, lack of design codes,
and most importantly, lack of awareness.
Applications of FRP Composites in Construction
There are three broad divisions into which applications of FRP in civil engineering can be
classified: applications for new construction, repair and rehabilitation applications, and architectural applications.
have been used widely by civil engineers in the design of new construction. Structures such as bridges and columns built completely
out of FRP composites have demonstrated exceptional durability, and effective resistance to effects of environmental exposure.
Pre-stressing tendons, reinforcing bars, grid reinforcement (Figure 3), and dowels are all examples of the many diverse applications
of FRP in new structures.
One of the most common uses for FRP involves the repair and rehabilitation of damaged or deteriorating
structures. Several companies across the world are beginning to wrap damaged bridge piers to prevent collapse and steel-reinforced
columns to improve the structural integrity and to prevent buckling of the reinforcement.
Architects have also discovered
the many applications for which FRP can be used. These include structures such as siding/cladding, roofing, flooring and partitions.
Intelligent Sensing for Innovative Structures (ISIS) Canada is a program that consists of
collaborative research and development efforts of Canadian Universities in various engineering disciplines. Its primary
mission is in the development of innovative uses of FRPs in concrete structures.
In Canada, engineers have integrated fibre optic sensors into numerous FRP-reinforced
systems to ensure that adequate supervision of the systems is provided.
Current Research on FRP
A serious matter relating to the use of FRPs in civil applications is the lack
of design codes and specifications. For nearly a decade now, researchers from Canada, Europe, and Japan have been collaborating
their efforts in hope of developing such documents to provide guidance for engineers designing FRP structures.
Natalie Y.L. Chung, who started her career in structural engineering in 1997, completed
her final year at Queen's University in Kingston in May 2002. Relevant work experience includes the design
of reinforced concrete, structural steel, masonry and timber structures. Over the years, she has developed many solid friendships
with professionals and academics in the engineering industry. Should you require additional information about FRP or
Canadian codes or standards, please contact individuals on the following site http://www.civil.queensu.ca/research/structural.htm or contact Natalie by email.