STRENGTH OF INTERMEDIATE LENGTH TUBULAR STEEL COLUMNS – BARE, CONCRETE FILLED, RETROFITTED OR REHABILITATED

Steel tubular members are used in high rise buildings, industrial structures, piles, bridge piers and offshore
structures. The strength 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 ongoing research on
concrete infilled steel tubular sections has the following aspects: (1) Steel tubulars of length 1200 mm infilled
with concrete of grades 30, 60 and 80 N/mm2 tested in axial compression and comparison with the code
predicted ultimate strengths using EC4, BS5400, ACI, AS and AIJ. The results show that BS5400 predicted
values were 30% lower than experimental results whereas ACI, AS and AIJ predictions were 5% higher for
concrete 60Mpa and 80 MPa. (2) Rehabilitation of artificially damaged tubulars using concrete, grout and
CFRP sheets. The “artificial damage” simulating typical patch corrosion reduced the ultimate strength by 5-
23%. Concrete filled tubulars when corroded had reduced strength by 40-50%. The several retrofit methods
showed significant increase in strength. However, grout infill showed highest strength gain, followed by
concrete infill. CFRP retrofit showed only limited increase.