This presentation is part of the Mid-Century Modern Structures: Materials and Preservation Symposium, April 14-16, 2015, St. Louis, Missouri.

Structural and Material Evaluation of Thin Shell Concrete (Hyperbolic Paraboloid) Structures in the Pacific Northwest
By Tyler S. Sprague

The Pacific Northwest is home to a large collection of mid-century thin shell concrete buildings. The popularity of this construction method was due in large part to the prolific creative work of John V. “Jack” Christiansen, who designed over 60 free-standing structures throughout Washington State. His work included the now-demolished Seattle Kingdome, formerly the largest concrete dome in the world. The most common structural form used by Christiansen (and others) was the hyperbolic paraboloid – a warped surface generated by the rotation of straight-lines. This surface was used in a variety of structural configurations, creating many different types of architectural spaces.

The majority of these structures are now over 50 years old, and demonstrating various states of material degradation and structural integrity. They collectively present a particularly challenging set of preservation issues. Located throughout the region, these buildings were designed for many different programmatic functions, in a variety of geographic locations. This presentation surveys the current state of several extant thin shell concrete structures in the Pacific Northwest, comparing their structural design (configuration, shell thickness) and climatic condition (rainfall, temperature range), with their current concrete quality, waterproofing strategies and issues, maintenance history and overall condition.

While Western Washington is known for heavy rainfall, the annual temperature changes are relatively modest. Conversely, Eastern Washington has far less rainfall, but significantly larger temperature changes. The comparison of these two climatic zones – and their effect on thin shell concrete construction – will provide valuable information for other preservation practitioners. In addition, by focusing on the specific structural configuration of the shells (inverted umbrella, gable, etc.), the structural forces of tension, compression and shear can be identified and compared to the current building condition. For example, vertical cracks in areas of tension or diagonal cracks in areas of shear would indicate structural capacity concerns – a very different condition from those arising from water intrusion. These specific inquiries compliment a more general assessment of the buildings’ overall condition, and indicate where more in depth evaluations techniques are needed.

While this presentation focuses on the Pacific Northwest, hyperbolic paraboloid structures of thin shell concrete were commonly built throughout the United States. Building off earlier scholarship, this research will be especially useful in other conservation efforts, and help suggest, if needed, remediation and repair strategies.

Speaker Bio

Tyler S. Sprague, P.E., Ph.D., LEED AP is an Assistant Professor in the Department of Architecture at the University of Washington, where he teaches courses in architecture, structural design and preservation. Dr. Sprague has engineering degrees from UC Berkeley and the University of Washington, professional experience as a structural engineer, and his Ph.D. in the College of Built Environments at the UW. Dr. Sprague has received grants from the Center for the Study of the Pacific Northwest (UW) and the regional chapter of the Society of Architectural Historians to survey the thin shell structures in the region.

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