Sustainable design integration for structural engineers

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    Design integration, in general, is not a new idea. For decades, structural engineers have seen how close collaboration with other project team members has led to the creation of some very unique buildings. Unfortunately, design integration is often overlooked when teams collaborate on more typical structures. Structural engineers have traditionally been limited to providing input only after the core building concepts have been decided. However, structural engineers should not limit themselves to the perceived boundaries of their expertise. Sustainable design integration is a call to action for structural engineers to become more involved with the early conceptualization of a building project. From the perspective of environmental sustainability, we can think of building design in terms of three key natural elements: the sun, the wind, and the earth.

    The sun

    At the beginning of any building project, it is extremely important to consider the relationship of a building to the sun path in the sky throughout the year. One of the greatest ways in which a building can be more efficient with regard to energy costs is to adapt its form, proportions, and materials to harness the sun’s benefits, while also shielding the building from the sun’s less desirable effects. Thermal mass concepts of storing the sun’s heat during the day and then later releasing this heat during the cooler evening can be an effective structural strategy when massive concrete or masonry walls are employed in the building design. Exterior sun screening and façade systems that diffuse the direct solar heat gain during the day can work together with exposed structural steel framing components to not only provide relief from the heat of the sun, but to also provide an interesting architectural expression. Consideration and coordination of day lighting and exterior views with the placement of solid shear walls and moment or braced-frame structures are important not only because of the reduced demand for energy consumption from artificial lighting, but also because of the psychological benefits from maintaining connections with the outdoors.

    The wind

    As structural engineers, we are used to designing our buildings to withstand the effects of wind loading, providing our structures with both adequate strength and stiffness. However, wind effects on a building structure are also an important sustainable design strategy. To the extent that it is practical, natural ventilation techniques of cross and stack ventilation can integrate with the building structure when floor plate depth ratios, floor diaphragm openings, floor framing orientation, and structural wall placement are thoughtfully proposed. Site placement and orientation of the building itself are important considerations when creating a relationship with the regional prevailing winds. Micro climates create site-specific wind effects that can be channeled by structural elements such as exterior screen walls. For certain structures, roofs can be sloped or shaped to enhance ventilation with aerodynamic effects. When considering the internal winds of a conditioned building environment, strategies such as displacement ventilation must be structurally coordinated with the air distribution requirements of raised floor systems. Floor slabs can be considered as a strategic base for radiant heating systems. Thermal breaks at exterior balcony structural slabs are important in maintaining an efficient interior heating and cooling system.

    The earth

    Depending on the given site topography, a building can sometimes be sited into a hillside in order to take advantage of the inherent heating and cooling benefits gained from the surrounding subsurface temperatures. With substructures such as these, retaining walls must be coordinated and detailed for both structural loading and to prevent water infiltration. Using a similar strategy, green roofs can be used to provide significant heat relief during the summer months and freeze protection during the winter; the structural engineer must consider the coordination of structural loading and detailing for green roof framing systems. Water collection and reuse is also a sustainable strategy in reducing surface runoff and its load on the civil infrastructure, and green roofs can also slow down the storm runoff effect. Besides green roofs, structural roofs can also be sloped and shaped to channel storm runoff into water collection systems for reuse as grey water. The selection of certain foundation systems can reduce unnecessary excavation and soil removal. Even the construction process itself deserves attention when considering sustainable design integration by reducing the waste involved with traditional construction practices.

    Sustainable design integration has led project teams toward the emergence of innovative ideas that cross disciplinary boundaries. If we are to move toward a truly holistic design philosophy, structural engineers must call upon themselves to adapt to different ways of thinking about how their structures are conceived and built.

    Ultimately our designs need to satisfy concerns for safety, serviceability, and sustainability. We as structural engineers must strive to wear multiple hats in order to contribute in a significant and meaningful way to the sustainable efforts of the design and construction team.

    Ruben Aya-Welland, S.E., P.E., LEED AP, is a project engineer for Hellmuth, Obata + Kassabaum (HOK), a multi-disciplinary architectural firm headquartered in St. Louis. He can be reached at ruben.ayawelland@hok.com. Aya-Welland is a member of the ASCE Structural Engineering Institute’s Sustainability Committee. The committee website is www.seinstitute.org/committees/sustainable.cfm.