Optimal design of reinforced concrete columns strengthened with square steel tubes and sandwiched concrete

The effectiveness of retrofitting reinforced concrete (RC) columns with steel tubes and sandwiched concrete has been confirmed through numerous studies. However, it is necessary to establish a strengthening design method that focuses on cost minimization to ensure the widespread application of the strengthening technology. Therefore, this paper presents an optimisation design study on circular RC column strengthened with square steel tubes and sandwiched concrete (SSTSC) jackets. Experimental investigations were firstly conducted to determine the constraints needed in the optimisation design model, including the width-to-thickness ratio, minimum width of the steel tube, confinement ratio and slenderness ratio. A formula was then proposed to predict the ultimate capacities of the strengthened specimens. Finally, based on optimisation theory of the complex-shape method, an optimal design program was developed in MATLAB. The cost of the rehabilitation scheme was taken as the objective function, while the load-bearing capacity and other related requirements served as the constraint functions. The cost of the optimised specimens was reduced by 17.72% on average, verifying the effectiveness of the model. This investigation focused primarily the cost-efficiency of schemes for retrofitting circular RC columns with SSTSC jackets. The results of this study indicate that the cost of the strengthening process can be reduced, and is expected to promote the widespread application of the strengthening technology. Furthermore, the basic principle and the development process of the model can be used as a reference for the optimal design of other types of strengthening methods.