In the 1999 AISC-LRFD, the in-filled concrete strength ( f 0
c) of concrete-filled tube (CFT) columns is limited to a maximum value of
55 MPa (N/mm2). That limiting value is raised to 70 MPa in the 2005 AISC-LRFD. This study aims to assess if the LRFD CFT column formulas
are applicable to intermediate to long rectangular columns with higher concrete strengths. Twenty four specimens with f 0
c varying between 29 and
84 MPa were tested. Various formulas and relevant provisions for CFT columns as specified in the major design codes including AISC-LRFD, EC
4, AS-5100, and CSA S16-01 were examined and compared. The design CFT strength (Pu) predicted by the AISC-LRFD formulas and the test
results (Ptest) were found to be in good agreement. The higher f 0
c limiting value of 70 MPa proposed in the 2005 AISC-LRFD appears acceptable.
The test results reveal that the 1999 AISC-LRFD design strengths are conservative and tend to penalize these CFT columns with higher concrete
strength