Overview
Worldwide attention is given to the use of fiber reinforced polymer (FRP) materials in highway and civil structures. Their natural resistance to the corrosive effects of de-icing salts and marine environments represents an attractive feature for the construction industry. Over the years, corrosion of reinforcing and prestressing steel has been a major problem. Epoxy coated steel and cathodic protection systems are examples of the methods used to control or prevent corrosion. Some of these methods can be successful. However, the majority are too costly and produce mixed results.
The magnitude of the structural damage observed due to recent earthquakes in California, Japan and some other parts of the world indicate that many of our existing structures require capacity and ductility upgrades in order to resist future earthquakes. A large number of bridges and structures need to be repaired or replaced. However, the cost of upgrading the existing transportation infrastructure is a major concern.
Also, in many cases due to outdated or marginal design, poor construction, inferior materials, etc., structural members in a bridge or a building are classified as incapable of resisting the design loads. Practical guidelines for damage assessment and repair techniques are often sketchy or not available for the design engineers. Traditional methods used in many repair applications include external jacketing with concrete or steel collars, pressure grouting, bonding of steel plates to the member, or applying external post-tensioning tendons.
While many of these methods are applicable, the resulting increases in dead load, lack of aesthetics, problems associated with steel corrosion and high cost are undesirable. In addition, most often these methods require a long time for completion and therefore closure or limited use of the structure during the rehabilitation period. These limitations led to the need for research in the use of lightweight composite materials with higher corrosion resistance.
In recent years, a number of new fiber reinforced polymer (FRP) composite material systems and technologies have been developed. Such systems provide not only alternatives to traditional materials and structural repair systems, but also opportunities for simpler and more rapid rehabilitation. Some of these products have been successfully used in highway structures.
FRP composites consist of high strength fibers bonded together with a continuous polymer or resin matrix. The use of these materials can improve serviceability (e.g., deflections and cracking) as well as the ultimate strength of flexural members. Moreover, they can be applied while the structure is in use with negligible changes in the member dimensions.
Examples are included of the past and current research activities on FRP materials performed by the staff of SDR, Inc. The results of this research led to the development of the MAS2000 Fiber Wrap System. The system has been subjected to a variety of severe environments and load testing to assess its performance under adverse conditions.
Other advantages include high strength and stiffness-to-weight ratios, a high degree of chemical inertness, controllable thermal expansion, damping characteristics and electromagnetic neutrality.
FRP products can be formed into rods, grids, sheets and winding strands. Fibers make 40 % to 70% of the volume and are the principal load carrying elements. The polymer matrix, on the other hand, acts as a load transfer medium and protects fibers from environmental damage.
FRP materials have come to maturity, as related to short-term and long-term performance have been answered. Increased strength, long- term behavior (bond, creep, etc.), and fatigue performance along with durability are some of the fundamental aspects investigated in developing the MAS2000 Fiber Wrap System. It is designed not only to provide the needed additional strength but also to provide the desired long-term durability.
This innovative system is based on the results of many years of pioneering research and development, field applications and monitoring. Through this research, the outstanding benefits observed in the application of external bonding of FRP laminates have been such that the technique has been used for the rehabilitation of large structural systems, as can be seen in the case studies presented herein.
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