In the construction industry, the aim is to construct low-profit structures that meet the demand of residents and safety measures, and also sustainability and environment-friendly measures need to be ensured in the production. Due to defined regulations in design codes to ensure stress capacity, ductility, and constructive needs, the optimum design problems are highly constrained which makes it a nonlinear one in defining the optimum design variables. In the present study, an optimisation methodology is presented via the use of a metaheuristic method called Harmony Search (HS) for reinforced concrete (RC) column members that having minimised cost and CO2 emission. The investigation is done for single objective cases of cost and CO2 emission together with multi-objective optimisation. According to the results, CO2 emission optimisation highly increases the cost of the design, while multi-objective cases lead to more low-profit results in the reduction of CO2 emission.