Concrete girders or steel trusses constituting the foundation under a building? : A comparison regarding the block Forskaren in Stockholm

Abstract: Hagastaden is a new district in Stockholm that is growing, and many structures are being built. Kv Forskaren, a funnel-like office building, will be built above the Haga tunnel in an ongoing project. During the design phase, where Bjerking AB carried out the construction design, it has been concluded that heavy concrete beams or steel trusses need to be placed over the tunnel that will lead the loads to the massive tunnel walls from the intended building above. In 2016, the Swedish construction and real estate sector released 21 million tonnes of greenhouse gases. This is an increase of 2 million tonnes in comparison from the previous year. Since the choice of construction material is strongly linked to the environmental impact, it is extremely important to choose the material that contributes to least emissions. In order to determine which construction material, concrete or steel, from an environmental perspective is the most suitable to use, a simplified LCA for each material was performed. The study was based on processes that are in the production phase. Environmental indicators that were studied and compared were carbon dioxide equivalents, CO2-e. Furthermore, the purpose was also to compare costs for the manufacturing of the materials. In addition to these factors, an overall assessment was also considered, such as maintenance and fire protection. To be able to make a simplified LCA, the program Construction's environmental calculation tool, BM, was used. Before using the tool, calculations of the material quantities were made based on given drawings on Forskaren from Bjerking. In order to determine which design type is preferable in a holistic perspective, a literature study was also done. The LCA study showed that the steel trusses contributed the least emissions of carbon dioxide equivalents during the production phase. Based on the work done, it has been established that there are both advantages and disadvantages to the construction materials. An active choice of one of these must be based on the specific conditions and requirements that exist in a project.