PhD candidate in building technology, are keenly aware of the importance of focusing on structural embodied energy as well as operational energy use. Both are trained in architecture and structural engineering, and both are convinced of the power of computational design. They note in particular todays genetic algorithms, which perform design optimization based on an evolutionary metaphor: They generate populations of designs that are bred and mutated over time for better performance. Given a starting set, the computer calculates the operational and structural embodied energy for each building design and then tweaks certain features or aspects to generate a set of new designs with better characteristics. By repeating the process, the computer analyzes thousands and thousands of designs to produce a limited set for the architects consideration.These final designs are suggested by the computer as ones that are going to do well, says Brown. It would be much harder to find them through trial and error, just by guessing. So I think it changes the role of simulation analysis in the design process. Its not just a checking algorithm but is a way to actually help with creative design exploration.Challenging case studiesTo demonstrate the power of this approach, Mueller and Brown performed a series of case studies focusing on long-span buildings structures such as airport terminals, concert halls, and bus stations. Such buildings seemed a good subject for their analyses. For one thing, they pose a special modeling challenge: They often have large open spaces with unusual shapes and few interior columns, so they rely on systems of triangular trusses and frames working together to support the load of the building. The structural materials required for those systems make up a significant fraction of the embodied energy component, so they provide a good target for energy savings. In addition, the use of computer simulation early in the design process when the shape of the building is determined can have a major impact on embodied energy. Careful choice of the geometry and layout of the structure can reduce internal forces and decrease the amount of energy-intensive structural materials required for support.Two characteristic features of long-span buildings involve trading off operational and structural embodied energy. Already mentioned is the cantilevered overhang, a rigid surface extending out from the main part of a building, anchored only at its origin with no additional support along its length. Adding a carefully designed overhang can block sunlight and reduce cooling loads, but it increases embodied energy by requiring the use of extra structural material.The other aspect of interest is building height. According to Brown, increasing the height will spread out internal forces in the structure so that support systems can be thinner and more widely spaced. Making the structure taller can up to a point reduce the amount of building material required, and embodied energy will decline. But a taller building has more exterior surface the building envelope and a greater volume of air to be conditioned, both of which generally increase operational energy.To test those trade-offs in practical systems, Mueller and Brown analyzed three types of long-span