Curvature-relevant analysis of eccentrically loaded circular concrete-filled steel tube columns

The existence of curvature can reduce the effective confining pressure within concrete-filled steel tube (CFST) columns under eccentric compression. The existing analysis method ignores such an effect and still treats the confining pressure as constant across the whole section as if it is under axial compression. In this paper, the authors have made significant improvements on the existing model, so that the curvature effect can be taken into account to properly interpret the non-linear behaviour of eccentrically loaded CFST columns. Meanwhile, shortening between two hinges is an important data output in test programmes of this type, which has been completely neglected by the existing analysis method. This improved method also provides calculation steps to track the value of shortening for each load increment. Unknown parameters in this new method are determined on the basis of data fitting of 87 specimens from previous researchers' test programmes. The following parameters are incorporated in this study: effective tube length (660–4670 mm), diameter of tube (76–600 mm), tube thickness (1·52–8·81 mm), yield strength of tube (256·4–517·0 MPa), cylinder strength of concrete (26·42–112·70 MPa) and eccentricity (9·4–300 mm). The load–axial displacement, load–deflection and moment–curvature curves predicted by the new method agree well with their measured counterparts in the tests.