Optimising flat plate buildings based on carbon footprint using Branch-and-Reduce deterministic algorithm

Abstract

The construction industry has been identified as a significant contributor to the global environmental impacts. While Life Cycle Assessment and many environmental approaches as well as low-carbon materials are key areas of sustainable designs, optimisation methods have not been fully developed and integrated in the design process to enhance a building's sustainability. Although there are studies attempting to mitigate buildings' carbon footprints, most of them examine the major components (slab and column systems) separately, making it hard for structural engineers to apply their findings in a real project. This paper intends to address this limitation by introducing an innovative design methodology for the carbon optimisation of reinforced concrete buildings. A detailed formulation of a flat plate building's optimisation is presented, and an advanced Branch-and-Reduce deterministic algorithm is adopted to solve for minimum CO2 emissions. Compared to genetic algorithm, the proposed approach achieves a further 31% reduction in the building's embodied emissions.In this research, multiple case studies are optimised and analysed with respect to varying slab spans and numbers of stories. Overall, the optimisation algorithm performs more efficiently in buildings that are subjected to greater compressive loads, and the optimal designs tend to reduce the slab-to-column area ratio to obtain the best sustainable outcomes. Compared to the conventional designs, the optimised ones achieve 5.3–17.7% reduction in the total carbon emissions. From a correlation analysis, the column concrete strength, column size, and building's height are found to be the most significant design variables. Although the structural weight is closely related to the total embodied carbon in optimised buildings, solutions with greater material savings are not necessarily more environmentally superior. It is the balancing act between the design constraints, ratio of concrete and reinforcement consumption, and ratio of concrete and steel carbon coefficients that determines the most eco-friendly design option. Given a complex relation between design variables, a thorough optimisation problem and methodology as presented in this paper are highly effective and recommended in sustainable designs of concrete buildings. The obtained findings from the numerical applications could effectively guide structural designers towards sustainable design solutions that have the best environmental performance.