Decision-making in structural type selection at the early design stage in terms of carbon emissions and cost – insights from case studies of port mooring facilities

Abstract

To decarbonize the construction sector, it is essential to consider carbon emissions from the early design stage. Moreover, it is crucial to optimize design solutions by including the implementation of low-carbon materials and clean energy.This study aimed to clarify the relationship between embodied greenhouse gas (GHG) emissions and construction costs in decision-making at the early design stage and the effect of implementing low-carbon materials and clean energy on decision-making. Three case studies on port mooring facilities were conducted, focusing on the structural type selection in design. Considering the current supply chain, the results showed roughly positive correlations between embodied GHG emissions and construction costs in the structural type selection; 0.4–1.2 kg-CO₂eq was reduced per 1 United States dollar. Therefore, decision-making to reduce GHG emissions was also effective in reducing costs. However, low-carbon materials and clean energy could alter the optimal structural type for embodied GHG emissions and construction costs, leading to discrepancies in the optimal structural type among each perspective. In one case, the optimal structural type regarding GHG emission was the RC caisson-type quaywall in the current supply chain; however, the RC wharf became optimal when low-carbon steel products with GHG emission intensity reduced by more than 21% compared to the current were used. These findings highlighted that the application of low-carbon materials and clean energy should be considered from the early design stage toward achieving the best design solutions. Additionally, the growing need to weigh the value of GHG emissions and costs was suggested.