Behaviour of Concrete Filled Rectangular Steel Tube Column

Abstract

The Concrete Filled Steel Tube (CFST) member has many advantages compared with the conventional concrete structural member made of steel reinforcement. CFSTs are frequently used for columns, caissons and for piers, deep foundations because of their large compressive stiffness. The FEA modeling using ANSYS software is adopted to investigate the load versus lateral deflection behavior of the composite sections. The effects of steel tube thickness and strength of in-filled concrete tubes are examined. The size of the column is 140 x 160 x 1500 mm and the grades of concrete infill are M20, M30 and M40. The thickness of the tube is taken as 2 mm, 3 mm, 4 mm, 5 mm and 6 mm and, the D/t ratio varies from 26.67 to 80.00. Since past few decades, composite steel-concrete construction of column and girder is being used in the construction industry. These composite sections have the rigidity and formability of reinforced concrete with the strength and speed of construction associated with structure, thereby making them economical. The steel and the concrete element in a composite member complement each other ideally. Composite members consisting of rectangular steel tubes filled with concrete are extensively used in structures involving very large applied moments, particularly in zones of high seismic risk. Concrete Filled Tubes (CFTs) have been used as girder, beam and columns in frame structures. A steel hollow section in-filled with concrete has higher strength and larger stiffness than the conventional structural steel section and reinforced concrete. Composite column are structural members, which are mainly subjected to forces and end moments. The steel tube serves as a formwork for casting the concrete, which reduces the construction cost. No other reinforcement is needed since the tube itself act as a longitudinal and lateral reinforcements for the concrete core. The continuous provided to the concrete core by the steel tube enhances the core's strength and ductility. The concrete core delays bending and buckling of the steel tube, while steel tube prevents the concrete from spalling. Also concrete filled tube (CFT) columns are suitable for tall buildings in high seismic regions since concrete delays the local buckling of steel hollow sections and increases the ductility of the section significantly. While there is a large number of studies on the behaviour of CFT columns and beam-columns; there is relatively little research reported on the flexural behaviour of concrete-filled hollow structural steel column. The structural behavior of a CFT is governed by the member strength, reflecting the fact that the load resistance is dependent not only on the material properties but also on the geometric properties of the entire member. Tests on CFTs by Bridge showed that the concrete core only provides approximately 7.5% of the capacity in members under pure bending. Lu and Kennedy studied strength on twelve beams of concrete-filled Steel Square and Rectangular Hollow Sections for examining the effects of different depth to width ratios and different values of shear span to depth. The tests showed that the ultimate flexural strengths of the composite beams are increased by about 10% - 30% over that of bare steel sections, depending on the relative proportions of steel and concrete. Although composite columns of concrete and steel were rarely used from the end of World War II until the early 1970s (Viest et al. 1997, 1.13), research had started a long time before, at the beginning of the 20th century. Combining of these materials had a number of motivations; steel columns were often encased in concrete to protect them from fire, while concrete columns were combined with structural steel as reinforcement. The model is created for different width-to-wall thickness ratios (from 26.67 to 80.00) and different concrete cube strengths (27.8, 42, 51 MPa). It is found that in general, concrete filling of the steel tube enhances strength, ductility and energy absorption especially for thinner sections. Han proposed a mechanics model that can predict the behaviour of concrete-filled hollow structural sections. In this paper, CFTs with three different wall thicknesses (Table 1) are selected (D/t = 26.67 - 80.00). Three different grades of concrete in-fills are considered. An effort is made to find the relative contributions of the steel tube and the confined concrete core to the moment capacity and deformation of CFTs under flexure.