Other forces
Buildings must be engineered to sustain gravity loads—as architects reach for loftier heights, gravity loads, along with lateral loads such as seismic forces and wind, increase the challenges of design. The dead load of terra cotta tiles and systems is approximately 5 to 6.5 kg/m2 (11 to 14 lb/sf).
Both curtain walls and terra cotta rainscreen systems—including curtain wall assemblies with infills combining glass and terra cotta—are commonly fabricated with aluminum framing. Aluminum framing construction is relatively lighter than steel, and is less susceptible to the brittle fractures experienced with materials such as iron (used in the early days of skyscraper design). Aluminum framing does not carry floor or roof loads, but transfers them to the building. Wind and gravity loads of the curtain wall or rainscreen system are also transferred to the building structure, typically at the floor line. (For more information, access Vigener and Brown’s Building Envelope Design Guide at www.wbdg.org/design/env_fenestration_cw.php.)
Façades are engineered to reduce any movement and sway caused by wind and seismic activity. Custom-designed systems can be engineered to accommodate a project’s anticipated amount of movement. This allows the system to adapt to differences in movement between the structure and the thermal movement of the metal frame. Additionally, rainscreen systems can transfer lateral outside pressure from wind load to the inside cavity. When installed properly, terra cotta rainscreens can reduce wind loads by equalizing the pressure on both sides of the cladding. However, the specific performance of such assemblies varies according to the materials and construction methods used.
Conclusion
Ongoing urbanization will continue to feed the trend of building upward. (Ali’s Art of the Skyscraper: The Genius of Fazlur Khan can provide further reading on this subject.) Design trends for tall buildings will continue to reflect the need for both structural efficiency and dynamic performance, and for accommodating the ever-evolving aesthetic goals of the design industry. In this environment of urbanization, one of the most versatile materials available to the architect and designer is terra cotta. Proven by its use over more than two millennia, terra cotta meets the changing physical challenges of construction while providing innovative options for forward-looking architecture, setting the stage for compelling urban environments.
Christian Lehmann is the general manager of NBK North America, beginning with the company more than 20 years ago as a ceramic engineer in Germany. He was instrumental in the development of the Terrart terra cotta façade product line and set up the manufacturing operations to produce it in Germany, Portugal, and China. Lehmann has initiated sales operations both in the United States and the Asian market. He can be reached at info@nbkusa.com.
