Analytical Confining Model of Square Reinforced Concrete Columns using External Steel Collars

摘要

Confinement in concrete column has been well known to improve its strength and ductility. Up to present, traditional transverse steel is still used as internal confinement in concrete column. Many researchers have proposed various stress-strain relationships for confined concrete under different conditions. In general, all these models suggested increases both in compressive strength and ductility. The improved ductility is characterized by the increase of ultimate compressive strain and the flatter post-peak descending branch of the curve. Recently, research on concrete confinement has been developed further from internal to external techniques. The increasing demand of reinforced concrete column retrofits is the main reason to develop such techniques. Some external techniques have been proven to be successful in retrofitting circular concrete columns. Experimental programs as well as confining models for externally confined circular columns have been developed. However, it is hard to provide an effective confining stress by external retrofit on square or rectangular concrete column. The non-uniform confining stress on column was due to high stress concentration at the column corners. Only a few experimental and analytical studies addressed these issues. This paper proposes an analytical model for predicting the peak strength of square concrete columns confined by external retrofit as well as the shape of the improved stress-strain curve. Analytical study is also presented to provide a brief idea on the proposed analytical model in comparison with some developed models. The proposed model is also compared with the experimental results by other researchers. It is shown that the proposed analytical model can predict the behavior of externally retrofitted square concrete columns reasonably well.