BEHAVIOUR OF TUBULAR STEEL COLUMN – BARE, CONCRETE FILLED AND RETROFITTED

Steel tubular members are used in high rise buildings, industrial structures, piles, bridge piers and offshore structures. In some applications the bare sections are used, in others they are infilled with concrete. Tubulars damaged due to corrosion or indentation are rehabilitated
by infilling with grout or concrete. The behaviour of short length steel tubular – bare or infilled with normal concrete – is widely reported. The codes provide expressions for evaluating the nominal strength of short and long, bare and infilled steel columns. Not many studies on intermediate length steel columns are reported. The research on concrete infilled steel tubular sections studied the following aspects: (1) Short Steel tubular members Circular Hollow Sections CHS30 and CHS50 were infilled with concrete of grade 30, 60 and 80MPa and grout and tested in axial compression. The slenderness was kept below limiting values for short columns, namely 50. The experimental values were compared with ultimate strength predictions of codes EC4, BS5400, ACI, AS and AIJ (2) Steel tubulars of intermediate length, with slenderness in between 50 and 200, and length 1200 mm infilled with concrete of grades 30, 60 and 80 MPa were tested in axial compression and compared with code predicted ultimate strengths using EC4, BS5400, ACI, AS and AIJ. External
diameter-to-plate thickness (D/t) ratios ranged from 11 to 14. (3) Rehabilitation of “artificially damaged” tubulars using concrete and grout. The “artificial damage” simulated patch type corrosion commonly seen in offshore tubulars. The artificial damage is obtained by grinding an area of the surface to a specific width, height and reduced wall thickness. The specimens were tested in axial compression. Similar damaged columns specimens were retrofitted using concrete and grout. The rehabilitated strength is compared to the original strength of the tubular for determining the effectiveness of the infill.