Concrete-Filled Tubular Steel Columns Under Eccentric Loading

The elasto-plastic behaviour of pin-ended, concrete-filled tubular steel columns, loaded either concentrically or eccentrically about one axis, is studied numerically. It is assumed that complete interaction takes place between the steel and the concrete, and each material is subjected to a uniaxial state of stress (i.e. triaxial and biaxial effects are not considered). The concentrically-loaded straight column is analysed by the tangent-modulus approach. The eccentrically-loaded column is analysed both by determining the 'exact' deflected shape and by assuming this shape to be part of a cosine wave; this assumption greatly simplifies the analysis and gives only slightly lower maximum loads. Experiments have been conducted on 18 eccentrically-loaded columns. The results of these experiments, and of experiments conducted elsewhere, have been compared with the numercial solution. There is good agreement between the experimental and theoretical behaviour of columns with lld ratios greater than 15 and it may be inferred that triaxial effects are small for such columns. For smaller lld ratios, columns with small eccentricity may show some gain in strength due to triaxial effect, and in this respect the calculated failure loads are conservative.

P.K. Neogi, H.K. Sen and J.C. Chapman