Experimental study on rectangular CFT columns with high-strength concrete

In the 1999 AISC-LRFD, the in-filled concrete strength 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 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 (P_u) predicted by the AISC-LRFD formulas and the test results were found to be in good agreement. The higher 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.