Concrete filled tubular columns (CFT) have been used in buildings and bridges since long in history, and research reported in china is since 1970s. It has become popular as structural members due to their excellent structural performance characteristics, which include high strength, stiffness and high ductility. In modern building construction, steel rectangular hollow sections (RHS), square hollow sections (SHS) and circular hollow sections (CHS) are often filled with concrete to form a composite column. Such composite columns are well recognized in view of their high load carrying capacity, fast construction, small cross section, and high fire resistance. Compared to concrete-filled steel tubular (CFT) columns, the DSCFT can reduce its own weight while have a high flexural stiffness. Compared to traditional RC bridge columns and CFT columns it has high bending stiffness, avoids instability under external pressure, is light weight, possesses good damping characteristics due to increase in section modulus. In present study it is found that there is a definite increase in strength. Circular columns had all the properties better than other geometric shapes; strength increase was almost 20 % as compared to square columns. It is expected that if same ratios are maintained at projected scale, there would be a definite increase in strength and behavior of the columns. New concept of hollowness introduced is valid for all geometric shapes in DSCFTs and gives fairly good idea about its limits and effects on strength of columns. The equations given in different design codes give conservative values and hence need to be revised for DSCFTs both for seismic and normal designs.
Axial Loading Behaviors of Square Concrete-Filled Tubular Columns with Large Width-to-Thickness Ratio Retrofitted using Carbon Fiber Reinforced Polymer Sheets(CFRP Sheets)