Ductility Study of the Slenderness Effects on SFRP Wrapped Plain Concrete Columns

摘要

Ductility of concrete columns is a very important factor to consider for retrofitting applications to ensure that the structure meets the new design codes/guidelines and can also withstand earthquake loading. A commonly adopted technique to enhance the ductility of columns is to wrap the concrete with Fibre Reinforced Polymers (FRP) sheets. Carbon FRP (CFRP), Glass FRP (GFRP) and Aramid FRP (AFRP) have been extensively used. However, very limited studies used the newly developed Steel FRP (SFRP). Furthermore, there is no information available in the literature concerning the slenderness effects on the ductility of concrete specimens wrapped with SFRP sheets which is the subject of this paper. The experimental program included eighteen specimens with varying slenderness ratios (HID, where H is the height and D is the diameter of the concrete column) of 2 (150 mm × 300 mm), 4 (150 mm × 600 mm), and 6 (150 mm × 900 mm). Each group included six three unwrapped control specimens and three wrapped specimens with one layer of SFRP sheet. All the specimens were loaded in uniaxial compression until failure. Two different methods of ductility analysis were investigated: the first method is based on the energy approach determined as the total area under the axial stress-axial strain curve. The other method is based on the ductility index parameter which is a function of the unconfined concrete strain and the ultimate axial strain. The results from the two ductility methods showed that wrapping the concrete columns with SFRP sheets improved the ductility over the unwrapped concrete specimens. The energy approach method resulted in decreasing the energy index with increase in the column height, whereas the ductility index method showed that the optimum ductility was obtained for the specimens with aspect ratio of 4.