Retrofitting of Columns

In recent years, the construction industry has experienced an increasing demand to restore, strengthen and upgrade existing structures. This may be attributed to various causes such as environment degradation, design inadequacies, poor construction practices, lack of regular maintenance, revision of codes of practice, increase in loads and seismic conditions etc.

All structures are susceptible for damage during earthquake. During a severe earthquake, the structure is likely to undergo inelastic deformation and has to depend on ductility and energy absorption capacity to avoid collapse. Buildings designed for gravity loading need to be strengthened to increase strength, stiffness and ductility.

Studies on the behavior of large-scale rectangular columns shows that the higher aspect ratio resulted in a reduction in the confinement pressure and the compressive strength of a confined column increased as the corner radius increased. The behavior of FRP wrapped concrete cylinders with different wrapping materials and bonding dimensions has been studied by using the finite element method (FEM) and other analytical methods. It was found that the load-carrying capacity of the wrapped concrete structure is governed by mechanical properties such as tensile elasticity modulus and Poisson’s ratio of the wrapping sheet.

According to conducted tests on models of circular cylindrical columns of concrete with GFRP jackets subjected to axial loading for different heights of cylinders, it was found that the increase in number of layers led to an increase in the maximum load. Researchers conducted tests on square prismatic concrete column, strengthened with external glass fiber composite. It was found that the stiffness of the applied FRP jacket was the key parameter in the design of external jacket retrofits.

They also have investigated the seismic behavior of concrete columns confined with steel and FRP. It was concluded that the use of FRP significantly enhances strength, ductility, and energy absorption capacity of columns. In 2003 it was investigated the retrofit of square concrete columns with Carbon Fiber Reinforced Polymer (CFRP) for seismic resistance.

It was found that added confinement with CFRP at critical locations enhanced ductility, energy dissipation capacity and strength of all substandard members.