Environmental- and life cycle cost impact of reused steel structures: A case study

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The European steel sector has developed LCA assessment methods over many years, methods taking into account benefits of recycling. Unlike recycling, the reuse of steel structures extends the steel life with lower impacts, because steel recovery through melting process is not needed. Benefits based on the savings in natural/virgin resources seem to be obvious by re-using materials, structures or buildings and giving them second, third or even fourth life. However, to show the benefits with the using a well justified methodological framework is not easy or straightforward as assumptions about the future reuse should be made. End of life processes, further processing, material identification and possible modification, and re-construction are the processes should be evaluated for the reuse case. Earlier studies have shown difficulties in the analysis of realistic economic impacts of reuse concepts. The number of possible alternatives is high and in worst cases, the reuse could lower the benefits compared to steel recycling. This theoretical case study is a part of PROGRESS project (Provisions for greater reuse of steel structures). The goal is to show the greenhouse gas impacts (as GWP) and life cycle costing (LCC) of the steel framed industrial building for the first life cycle and for the case of steel frame and envelope reuse. The study pointing out benefits and loads and by discussing the meaning of methodological differences when using building Life Cycle Assessment methods (LCA). The improvement of the design methods for portal frames is one of the recurring topics in the field of steel structures. Due to the large number of similar framed structures, the desire to “automate” the design and manufacturing process was popular from the very early stage. As Dowling et al. (1982) noted, there are two design tendencies when trying to achieve more economical solutions: (a) to use compact hot-rolled sections and exploit the advantages of plastic design and (b) to use slender built-up sections with the most advantageous distribution of the material but keep the design in the elastic range. The second option usually leads to slender structures, and therefore stability becomes the main concern of the designer. One of the outcomes of RFCS project PRECASTEEL was a database of optimized constructional steelwork for industrial buildings (Precasteel web 2.0 application, 2011) that is able to resist up to 1500 N/m2 of vertical snow load and appropriate horizontal wind load or seismic load with the peak ground acceleration (PGA) up to 0.32 g. Figure 1. Loads and basic dimensions of the optimized frames The frames (welded-tapered, hot-rolled and truss girders) were optimized to minimize the steel consumption with sufficient structural resistance and stability using advanced 3D finite element models and genetic algorithms as optimization and simulation methods (Figures 1 and 2). One of the optimized solutions with welded-tapered frames was selected for the purpose of this study. Since the building shall be erected in Finland, heavy snow load (1500 N/m2) was assumed, but no seismic loading. The span of the frame is 16 m and eaves height is 6 m, which leads to steel consumption of the primary structure under 20 kg/m2 (Figure 3). The total length of the building is 30 m with six identical frames at 5 m spacing. This theoretical study takes into account optimized steel structures. Figure 2. Example of lateral-torsional buckling failure of 3D FEM model used for optimization of the structural shape. Figure 3. Steel consumption of welded-tapered frames with different heights and snow loads 3 LIFE-CYCLE ASSESSMENT Life cycle assessment method (LCA) was chosen for the evaluation of the environmental(SFS-EN ISO 14044:2006, EN 15978:2011) of the industrial building. The main goal is to show the potential of environmental performance and improvements through comparison of new hall construction (‘New building’) and steelwork with reused steel components (‘Reused steel’).