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Efforts are being made to achieve more efficient operation of buildings, with the goal of reducing the construction industry's contribution to energy consumption and greenhouse gas emissions. That contribution also includes the energy embodied in structures; that is, the energy consumed in the processes of extracting, manufacturing, transporting, and installing construction materials (including recycled materials) and elements. In particular, in spite of the use of additives such as fly ash, reinforced concrete (RC) structures, which are large consumers of cement, are responsible for a sizable proportion of worldwide carbon emissions. These emissions can be reduced significantly through the more efficient use of both concrete and steel that can be achieved by optimization. Modern optimization tools are now available that make it possible to perform large volumes of calculations efficiently that are applicable to a wide variety of structural engineering problems. This study presents an optimization approach developed with a view to allowing decision makers to balance sustainability and economic objectives. To illustrate this approach, an RC frame under gravity and lateral loads is considered in this paper. It was found that, depending upon the parameter values used in the calculations, the design optimized with respect to the CO 2 footprint yields a CO 2 footprint that is lower (by 5% to 10%) than the design optimized with respect to cost. The reduction can be smaller for low-rise structures and other structures with predominantly tension-controlled members. However, for structures whose members predominantly experience large compressive forces, such as high-rise buildings, the reduction may be more significant. This also may be true of certain prestressed and poststressed concrete members. Additional research aimed at ascertaining the extent to which this is the case is warranted.

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