Axial compressive behaviour of concrete encased extended I-shaped steel composite stub columns with less reinforcement

Abstract

A novel concrete encased extended I-shaped steel composite (EI-CES) column with less reinforcement for prefabricated structures is proposed. Eight EI-CES stub columns with one covered by concrete fireproof board, and two bare extended I-shaped steel stub columns, are tested under axial compression loads. The effects of stirrup spacing, stirrup form, proportion of steel sectional area, and concrete compressive strength on the axial compressive behaviour of composite columns are studied by test and finite element analysis. According to the results, the concrete cover with less reinforcement can prevent internal steel instability under axial compression. 25 mm thickness of concrete cover can satisfy the load-carrying capacity and serviceability requirements for the composite column. The premature spalling of concrete cover can be prevented by installing fireproof board, reducing stirrup spacing, and using closed stirrups. The proportion of steel sectional area in composite columns increasing from 7.5 % to 9.6 % has no effect on the maximum material full-utilization coefficient, but can reduce premature concrete cracks and improve the residual strength of EI-CES columns. The concrete compressive strength in composite columns decreasing from C50 to C30 can improve the maximum material full-utilization coefficient and residual strength. The composite columns have excellent post-peak deformability. A formula for the axial resistance of EI-CES columns is proposed and validated.