Strength of preliminary compressed concrete-filled steel tubular columns with square cross-section

The strength of CFST columns with a square cross-section at axial and eccentrical compression operation with small eccentricities is noticeably lower, if compared with similar circular cross section columns. The paper suggests increasing the strength of CFST columns with square section by preliminary compressed concrete core implementation. The compression is carried out by a long pressing of the concrete mixes after column molding process completion. This paper's objective is to determine the efficiency of preliminary compression of the concrete core of CFST columns with a square cross-section, based on the strength experimental research. In order to test the effect on preliminary compression of concrete CFST, 4 series of laboratory column samples were manufactured and tested for the central compression with a short-term load. The samples of different series, varied in the original concrete class (C40 or C80), as well as the availability or lack of preliminary compression of the concrete core. The experimental research showed a gain in the strength of samples made of C40-class concrete by 13%, C80-class concrete – 20% and a significant increase of the fixture effect, due to the core preliminary compression. (paper)