ABSTRACT
ABSTRACT: When a building requires a long span, especially on the ground floor of a multistory building, the long span often determines the structural system used early in the design process without any other consideration. Commercial and residential buildings are responsible for roughly 40% of all carbon emissions and energy use, more than any other sector in the USA. Moreover, this excludes the significant energy and emissions required to extract, process, transport and assemble building components. Globally, the production of cement alone accounts for 4% of carbon dioxide emissions. Consequently, reducing the environmental impact of building construction and operations is critical to address interrelated issues such as global climate change. The role of structural systems in the overall performance of a building has been largely neglected. Very little consideration is given to other ways the structure could contribute to improving sustainable outcomes. This is in spite of the fact that the structure of a typical office building contributes roughly one-quarter of the total embodied energy and is, at the very least, the armature for all other building systems. Existing research into the embodied energy of structural systems focuses on hypothetical office buildings with uniform structural layouts, a range of comparable, existing office buildings or housing without comparing or accounting for the long spans. Like all other aspects of a building, the structural system needs to be understood in terms of wide range of sustainability issues: embodied energy, operational energy, longevity and reuse. If structural systems could be left exposed without additional finishes as well as be configured to provide a higher level of thermal comfort, more daylight and acoustic isolation, this could significantly reduce the operational energy and the initial materials required for new construction. These multi-performance structural systems, in contrast to high-performance structural materials that aim to only improve structural properties, offer considerable and largely untapped opportunities to improve new and existing buildings while potentially lowering construction costs. Using a five-story, 2,500 square-meter (27,000 square-foot) classroom building with 24.4 meters by 30.5 meters (80 feet by 100 feet) auditorium on the ground floor as a case study currently in design at Oregon State University, the multi-performance criteria for three long span systems, including steel, concrete and wood, are compared. These criteria include embodied energy and carbon, structural and spatial properties, acoustical properties, fire protection and thermal properties. This paper argues that the most efficient structural solution may not be the best in terms of overall sustainability outcomes, and the selection of a structural system should be based on multi-performance criteria.
