Calculating the Strength of Concrete Filled Steel Tube Columns of Solid and Ring Cross-Section

The authors have carried out experimental and theoretical studies of a new design of concrete filled steel tube (CFST) columns with pressed structure of concrete. The proposed design improvement idea is to make CFST columns with preliminary pressed concrete core. The bearing capacity of centrally compressed samples of CFST has increased by 20 divided by 25%. The obtained results are explained by a significant increase in the strength of concrete core in such preliminary compressed CFST samples due to the simultaneous manifestation of three effects: long-term compression of concrete mix, preliminary lateral compression of the concrete core and its work under the conditions of volume compression. The calculation of strength of CFST should be carried out on the basis of nonlinear reinforced concrete deformation model. Three-axis tensely-deformed conditions are assumed for the analytical description of work of the concrete core and the external steel holder. The basic dependencies, which allow to carry out such approximate calculations of the ultimate stress of compressed CFST, are resulted, too. (C) 2016 The Authors. Published by Elsevier Ltd.