Research on axial behaviour of concrete columns retrofitted with pre-stressed steel strips

In many cases today, concrete columns do not meet the requirements of current design codes due to a number of deficiencies, including low concrete strength, inadequate transverse rebar and low construction quality. This paper presents the results from an experimental study of a strapping method for retrofitting the axial performance of concrete columns. In the method explored herein, the high-strength steel strips surrounding the concrete columns are pre-stressed using an air pump to provide additional transverse confinement. To analyse the axial performance of cylindrical plain concrete columns retrofitted with pre-stressed steel strips, a static loading experiment was performed on 18 large-scale specimens. Failure mode, strain development and ultimate bearing capacity were thoroughly examined, and the effects of volumetric ratio, number of layers and spacing of steel strips were also considered. Test results show that the use of pre-stressed steel strips provides significant improvement in strength and deformability, and that the number of layers and spacing of the steel strips both play important roles in this regard. Finally, the calculations, which are based on the Newman model and regression analysis for predicting the retrofitted columns’ axial compressive strengths, are presented.