Best Tall Building Americas – Award of Excellence: 35XV, New York City

Joel Breitkopf
Alchemy Properties, New York City

Daniel Kaplan
Senior Partner
FXCollaborative, New York City

History of Unbonded Post-Tensioned Concrete in Skyscrapers

Unbonded post-tensioned (PT) concrete has become a widely-accepted construction technique in the United States. The introduction of PT in tall buildings has been relatively recent, but it has become the current standard for concrete deck reinforcement within the past 20 years. This significant advancement has allowed for greater flexibility in architectural interiors, reduced building construction and operation costs, and efficient, yet durable structural designs.

This presentation focuses on the history of post-tensioned skyscrapers in Chicago, with reference to its expansion into other US metros. Additionally, it provides a brief overview of the structural design and the manufacturing process, in order to produce an unbonded post-tensioning tendon. Furthermore, the presentation delves into the constructability benefits and concerns with unbonded post-tensioning in relation to current building codes and industry specifications. Several high-profile residential buildings and hotels in several US cities are highlighted to provide a connection to real-world examples.

Whereas unbonded post-tensioned has a proven track record in the United States, its commercial application is limited on a global scale. Therefore, unbonded post-tensioned concrete has great potential in the next 50 years to expand into new geographies. The key to its adoption is education within the engineering and construction community, as well as local investment in a manufacturing supply chain. Unbonded post-tensioned concrete has a place globally as a form of structural material in tall buildings.

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