Behaviour of steel-fibre-reinforced normal-strength concrete slender columns under cyclic loading

The inclusion of ductility requirements is necessary to guarantee the safety design of any concrete structure subjected to unexpected and/or reversal loads. It is important to outline that plastic hinges may be developed in columns of reinforced concrete buildings, especially in column-foundation joints. The deformation capacity of the column depends on its slenderness. However, few experimental tests of normal and fibre-reinforced concrete columns in the range of medium slenderness (between 5 and 10) have been performed for the case of cyclic loading. This paper presents an experimental research study on the behaviour of slender columns subjected to combinations of constant axial and lateral cyclic loads. In order to study the behaviour of this type of element fourteen experimental tests were performed. The experimental results make it possible to calibrate numerical models, and to validate simplified methods. The following variables are studied: slenderness, axial load level, transverse reinforcement ratio, and volumetric steel-fibre ratio. The maximum load and deformation capacity of the columns are analyzed. It is interesting to note that the deformation capacity depends on the four test variables analyzed. Moreover, the inclusion of steel fibres into the concrete mixture increases the deformation capacity. The inclusion of a minimum transverse reinforcement is required in order to improve the effectiveness of the steel fibres. Thus, the column behaviour suffers moderate strength losses due to cyclic loads. Finally, slenderness influences the deformation capacity if second-order effects are important, the cross-section displays ductile behaviour, and the capacity of the materials is reached.

► The inclusion of steel fibres improves the deformation capacity of columns.
► Minimum shear reinforcement is required to improve effectiveness of steel fibres.
► Slenderness affects ductility if second-order effects are important.
► In general, EC-8 code is on the safe side for medium to high axial loads.
► In columns with steel fibres, EC-8 code predictions are conservative.