Sustainability of long-span bridge launching techniques: emissions assessment and life cycle analysis

The construction of long-span bridges is a resource-intensive process with a substantial carbon footprint, largely determined during the construction phase. While Life Cycle Assessment (LCA) often focuses on materials, the environmental impact of the superstructure erection technique—particularly launching methods—remains insufficiently explored. This study addresses this gap by performing a comparative, construction-phase LCA of three launching techniques for a steel box-girder bridge: (1) assembly from below using heavy crawler cranes and temporary towers, (2) the Incremental Launching Method (ILM) with a lattice girder and Hydraulic Pushing Systems (HPS), and (3) an ILM variant using a temporary aerial-stay system. The assessment is based on a detailed case study of a 200-m-long bridge in complex topography (e.g., deep river valley requiring tall piers and restricted site accessibility). It quantifies CO₂-equivalent (CO₂eq) emissions by integrating a structural analysis of launching phases, an energy inventory of equipment, and emission factors for materials and diesel fuel. The results reveal a clear environmental hierarchy: the crane-based method exhibits the highest impact (270 tCO₂eq), primarily driven by sustained diesel consumption of heavy lifting equipment. The ILM with a lattice girder achieves the lowest emissions (240 tCO₂eq), corresponding to an approximate 12% reduction relative to the crane-based alternative, while the ILM with an aerial-stay system provides only a marginal improvement (265 tCO₂eq, about 2% reduction). The results indicate that the choice of launching technique can significantly influence construction-phase emissions and should therefore be explicitly considered in early-stage bridge design and construction planning.