“Green” Design Strategies Have Direct Impact on Structural Design
Victoria Arbitrio, PE, SECB, is an Associate Partner with the New York City office of Gilsanz Murray Steficek, a structural engineering and building envelope consulting firm. Ms. Arbitrio is currently a Director for the Applied Technology Council (ATC), and serves on the Metropolitan Region Board of Directors for the American Council of Engineering Companies of New York (ACEC-NY). She is also a Past President of the National Council of Structural Engineers Associations (NCSEA), and a member of the Structural Engineering Certification Board (SECB).
This article is part 3 of a 3-part series from the Structural Engineering Certification Board. The series explores the relationship among structural engineers and architects and the challenges and opportunities inherent in green building projects. Some of the information provided in this article was adapted from an article published in STRUCTURE Magazine, the official publication of the National Council of Structural Engineers Associations (NCSEA).
Click to read Part 1 and Part 2.
With green building becoming more widespread, the challenge to the design community is to move beyond simply green to develop sustainable, high-performing buildings. These buildings are more than just environmentally friendly. The design team must also consider the short and long term economic and social effects of the building’s design and construction. The structural engineer, as an integral part of the building team along with the architect and others, can significantly help the team recognize the impact that their “green” environmental, economic and social decisions will have on the building’s structural design, and vice versa.
According to the High Performance School Buildings Resource and Strategy Guide from the Sustainable Building Industry Council, sustainable, high performing buildings should adhere to sixteen principles in their design and construction. Many of these have direct implications for the structural design of the building. Let’s examine some of these to see why the structural engineer is an essential part of the “green” building team.
Daylight and Visual Comfort
Daylighting strategies can impact the structural design in several ways. Building orientation and the location of walls to provide views to the outside can limit the location of shear walls and other loadbearing elements in the building. Roof monitoring, clerestory windows and other openings must be considered when detailing the load path for the building structure.
Daylighting strategies can also include the use of light shelves, which are externally-mounted devices used to reflect light deep within a space. The loads from these devices, as well as other external shadings or cladding materials intended to provide visual comfort to occupants, must be considered in the structural design.
Environmentally Responsive Site Planning
This is a wide-ranging principle that includes such issues as storm water control, shading for parking and the use of vegetative roofs. Retaining walls can also play a role in stabilizing the site. An increasingly popular strategy that generally affects the structural design is the use of vegetative roofs. Such roofs may have several inches of soil and can impose much higher dead loads than a typical roof. Dead loads to be considered include the weight of the components of the green roof system such as geotextiles, drainage media, and plant materials, as well as the weight of the system when irrigation or rainfall has saturated the drainage layer.
Water Efficiency
Strategies used to improve water efficiency often include low-flow fixtures and rain water harvesting. Sloping roofs and water storage, with its associated weight, are issues that can impact the structural design. Water storage systems may be located on the ground, inside or outside the building or within the building at a height that provides distribution without pumping. Such loads can be significant. In some cases, the water storage system inside a building can be used as part of the structural damping system.
Acoustic Comfort
Many of the strategies used to improve acoustic performance include the use of heavier materials, because increasing material mass is one of the primary means to decrease sound transmission. The architect and structural engineer should be aware of the use of these materials, because the increased weight of extra gypsum board over studs or the use of interior masonry walls could have a significant effect on the structural design. The use of internal masonry walls for acoustic purposes also provides an opportunity for walls to serve multiple purposes when designed as part of a loadbearing masonry structure. If reinforceable acoustic block is used as a sound-isolating strategy, architects should collaborate with the structural engineer on the type of material used, since acoustic block can take many forms, depending upon the manufacturer, and these will impact their structural capacity.
Renewable Energy
Renewable energy sources such as photovoltaic panels are most often mounted on the roof of the building. In some cases, solar panels can impact the shape of the roof and so must be considered by the architect and structural engineer. The structural engineers must account for the panels and the equipment support system in their structural design.
Energy Efficient Building Envelope
One key to achieving an energy efficient building envelope is to control air movement. Detailing of air barriers is critical. Architects need to work with structural engineers ensure the cladding is adequately supported.
Thermal Comfort
One strategy used to minimize interior temperature swings is the use of thermal mass, interior masonry or exposed concrete walls. This increase in building weight must be designed for, but can also provide an opportunity for creating an efficient structural design.
High Performance HVAC
While there are many strategies for high performance HVAC, one that affects the structural design is the use of natural ventilation in the building. Among the factors the structural design must take into account are the influence of wind in the building and the impact of thermal chimneys and vertical spaces that are designed to draw heat and air out of the building.
Safety and Security
Beyond the simple life safety of the structure, the structural design must also account for many unique aspects of safety and security: blast resistance, impact resistance and fire resistance. Skilled structural engineers are familiar with the requirements for blast resistance for government buildings. Impact resistance to large impacts and wind-borne debris can also affect the design of the structure. Compartmentation, using masonry or concrete walls to sub-divide the structure for fire resistance, can also be incorporated into the load bearing design of the building.
Choosing Environmentally Friendly Building Materials
Architects and structural engineers have a great opportunity to collaborate when determining the materials to use. Of particular importance to the structural design, beyond its environmental impact, are durability and performance of the materials. The architect may take the lead in choosing materials, but the structural engineer should take the lead in evaluating what impact the materials will have on the structural design and whether alternative materials would better serve the team’s effort to design and build an excellent sustainable, high performing building.