FRP as a retrofitting solution
Generally structures are subjected to natural and man-made loads during their service life. When the magnitude of these loads exceed the capacity or strength of the structures, they are likely to be damaged. Sometimes the strength of a structure is reduced because of the use of substandard materials in its construction or due to the application of additional load because of change in functioning or due to seismic forces for which the structure had not been designed originally. These situations warrant strengthening or up-gradation of the structure to carry the enhanced loading. Considering the economy of putting up another new structure in place of the damaged structures with the associated loss of revenue due to interruption in the functioning of the structure as well as economic and environmental factors, a decision to repair the structure becomes essential.
A variety of structural up-gradation and retrofitting techniques has been evolved over the years for different structures and also has been used. Some methods of seismic upgrading such as addition of new structural frames or shear walls have been proven to be impractical because they have been either too costly or restricted in use to certain types of structures. Other strengthening methods are grout injection, insertion of reinforcing steel, pre-stressing, jacketing, different surface treatments, etc. Each of these methods involves the use of skilled labor and disrupts normal functions of the building. These well-known techniques may sometimes be inadequate for applications that should preserve architectural heritage with historical value. FRP composites are now increasingly used in the construction industry and offer considerable potential for greater use in buildings, including large primary structures. In recent years more complex applications have been developed to satisfy the desire for more dramatic features in building design. FRP composites have numerous potential advantages in building construction including the following:
- offsite fabrication
- modular construction
- reduced mass
- superior durability
- ability to mould complex forms
- special surface finishes and effects
- improved thermal insulation
- lack of cold bridging
As a repair material also confinement with polymeric matrix or Fiber Reinforced Plastic (FRP) composites presents significant advantages over a traditional confinement techniques: the cross sectional dimensions of the column do not increase, which permits compliance with architectural restraints; the mass of the column does not increase; which means that the seismic behavior of the building remains unchanged; the low weight of FRP materials implies that the installation procedure is faster, easier and less dangerous for the operator than implementation of traditional confining techniques, Modern techniques of confinement consist of wrapping with FRP sheets or laminates. They were introduced in engineering practice as an innovative confinement technique during the last decade as an alternative to wood or steel ties adopted in the past. Therefore the use of FRP laminates for retrofitting and strengthening is a valid alternative because of their small thickness, high strength-to-weight ratio and ease of applications.
FRP as a Retrofitting Solution for Cooling towers
The dry/wet loading cycle in cooling towers provides an ideal environment for corrosion of the structure. Many of these cooling towers are constructed with concrete, and the reinforcing steel corrodes after a short service life. In addition, larger cooling towers such as those used in the nuclear power industry include concrete beams and columns in the interior of the tower that corrode rapidly. Repairs must consider both a reinforcement scheme to replenish the area of steel lost to corrosion, and a protection mechanism to slow down the future corrosion rate of these elements. FRP fabrics and can be used to achieve both of the above objectives.