Influence of concrete compaction on the strength of concrete-filled steel RHS columns

Abstract Concrete-filled steel tubular columns have better structural performance than that of bare steel or reinforced concrete (R.C.). The use of concrete-filled SHS (Square Hollow Section) and RHS (Rectangular Hollow Section) have become widespread in the past few decades. However, these members are susceptible to the influence of concrete compaction. It is expected that the influence of concrete compaction on R.C. columns and concrete-filled steel tubes is different. For R.C. columns, concrete compaction only affects the mechanical properties of concrete. But for concrete-filled steel tubes, it is well known that the interaction between steel tube and concrete is the key issue to understand the behaviour of this kind of column. The concrete compaction not only affects the properties of the core concrete itself, but also may influence the interaction between the steel tube and its concrete core, and thus influences the behaviour of the composite columns. The present study is an attempt to study the influence of concrete compaction on the strength of concrete-filled steel RHS columns. Tests on 35 concrete-filled steel RHS columns to investigate the influence of concrete compaction methods on the member capacities of the composite columns are reported. The main parameters varied in the tests are: (1) column section depth-to-width ratio, from 1.0 to 2.0, (2) tube depth to thickness ratio, from 34 to 136, (3) load eccentricity (e), from 0 to 31 mm and (4) column slenderness (λ), from 21 to 62. The main objectives of these tests were twofold: firstly, to report a series of tests on composite columns under different concrete compaction methods; and secondly, to investigate the influence of concrete compaction on the member capacities of the composite columns. Comparisons are made with predicted column strengths using the existing codes such as LRFD, American Institute of Steel Construction Inc-1997, AIJ-Architectural Institute of Japan-1997, Eurocode 4-1996 and GJB4142-2000. It was found that better compaction of concrete resulted in higher member capacities in concrete-filled steel RHS columns. The tests showed the importance of good concrete compaction for concrete-filled steel RHS columns.