EFFECT OF STEEL WIRE FIBER ON COMPRESSIVE STRENGTH OF CONCRETE FILLED STEEL TUBULAR COMPOSITE COLUMNS

Abstract

The concrete filled steel tubular (CFST) column is a composite structure which consists of steel tube and concrete infilled core. This study presents an experimental investigation on the structural behavior and geometric parameters of CFST composite column due to the inclusion of GI fiber under concentric and eccentric loading. Addition of GI fiber in concrete infill is a cost effective way to improve the behavior of CFST column and it is also locally available. The design codes AISC-LRFD (2010), Australian Standard 4100 and Eurocode 4 were also studied and compared these code predicted capacities with the experimental results. Total twenty-nine (29) square shaped concrete filled steel columns were tested in this study. Among these columns, twelve (12) long column specimen and six (6) stub column specimen were made with 2.5 % of GI wire (weight basis). Three types of concrete strength (20, 30 and 40 MPa), three types of cross sections (100x100, 125x125 and 150x150 mm) and two types of tube thickness (4 and 5 mm) were used. The geometric variables were addition of GI fiber, cross sectional slenderness ratio (B/t), global slenderness ratio (L/B) and loading eccentricity ratio (e/B). The material variable considered as concrete compressive strength (fc/). The experimental capacity and loaddeflection curve of concrete filled steel tubular column with or without steel wire fiber were observed. The structural behavior as ductility index (DI) and mid-height deflection were also measured. From the results, the load carrying capacity was observed to be increased by 10-11% and average deformation capacity is increased by 30% with addition of GI fiber in the concrete. The ductility indexes were also increased by 25-30% which indicates improved ductile behavior of CFST column. Ultimate load capacity was increased by 15% and 10% with the increase of compressive strength for fibered and plain concrete, respectively; whereas, ductility was decreased by 4% and 15%, respectively. Ultimate load capacity, deformation and ductility were increased by 19%, 18% and 1.5%, respectively for decreasing the cross sectional slenderness ratio from 31.25 to 25 of CFST columns with plain concrete. For the fibered concrete, these increment were higher than plain concrete by 21%, 19% and 4%, respectively. Adding GI wire fiber into concrete delayed the local buckling of composite columns. It was observed from the experimental study that failure initiated at the middle and edge of the columns due to buckling of steel section followed by concrete crushing. Ultimate load carrying capacity matched with the AISC-LRFD (2010), Australian Standard 4100 and Eurocode 4 code predicted capacities with good accuracy (0.98-1.03). AISC-LRFD (2010) takes more conventional approach (Mean 1.01 and standard deviation 0.05) on determining the ultimate load carrying capacity of CFST columns. This experimental study indicates that the addition of GI fiber in core concrete has very significant effect on the strength and behavior of concrete filled steel tubular composite columns.