Hybrid harmony search for sustainable design of post-tensioned concrete box-girder pedestrian bridges

•The automatic design and CO2 optimization of post-tensioned concrete box-girder pedestrian bridges is studied.•A hybrid harmony search algorithm combined with threshold acceptance is described.•The findings indicate that the environmental goal also ensures economic solutions.•The CO2 optimization seeks greater depths, more strands and lower concrete strength.•One hundred years of carbon capture represents only 1% of the CO2 emissions.

This paper aims to find sustainable designs of post-tensioned concrete box-girder pedestrian bridges. A hybrid harmony search algorithm combining threshold optimization is used to find the geometry and the materials for which the sum of the costs or the emissions are the lowest, yet satisfying the requirements for structural safety and durability. An experimental design method was used to adjust the algorithm parameters. The parametric study was applied to three-span deck bridges ranging from 90 m to 130 m. The findings indicated that both objectives lead to similar cost results. However, the variables presented some differences. Such deviations suggested greater depths, more strands and a lower concrete strength for CO2 target functions. Carbonation captured less than 1% of the deck emissions over 100 years. This methodology leads to a precise analysis of the practical rules to achieve an environmental design approach.