Behaviour of concrete-filled steel tubes under static and variable repeated loading

This paper presents the results of static loading (SL) and variable repeated loading (VRL) tests on concrete filled steel tubular (CFST) columns. Assessment of the columns was based on its length, concrete strength and load eccentricity. The column behaviour (with and without filling) from the tests was studied. The ultimate strength of the columns subjected to VRL reduced by up to 16% after undergoing a number of load cycles. The incremental collapse (IC) limit was found to lie between 70% and 88% of the static collapse load for CFST columns. The deformations at IC limit were significant and could affect practical designs. The theoretical strengths of the stub and long columns tested are determined on the basis of building code 318 of the American Concrete Institute, and compared with the test results. The squash load equation of the code was found to underestimate the nominal strength of short composite columns.