ATX Tower, Austin: Pioneering Performance-Based Wind Design in High-Rise Construction

The University of Texas at Austin designed the ATX Tower, the first high-rise to incorporate the American Society of Civil Engineers (ASCE) Prestandard for Performance-Based Wind Design (PBWD). Currently the tower is under construction in Austin, Texas and after completion, by the end of 2025, is expected to transform the design of tall buildings for wind loads. This new design aims to enhance reliability, reduce carbon emissions, and increase cost efficiency.

ATX Tower specifically is located at 321 West 6th Street, will rise 58 stories and 671 feet above downtown, offering 561,000 square feet of office and residential space in the city’s historic entertainment district.

After its release, the focus was to find a suitable project to implement PBWD. After careful consideration, MKA and wind engineer CPP Wind Engineering Consultants determined that ATX Tower could be a potential candidate.

Therefore, in May 2021, to validate their decision, they conducted wind tunnel testing led by CPP Senior Principal Roy Denoon. Through multiple tests, they evaluated wind loads on the structure, cladding, and pedestrian environment using a 1:350 scale model, assessing wind influences from 36 directions.

Furthermore, MKA’s team to calculate the wind non-linear response created a detailed analysis model using non-linear properties to simulate inelastic behavior, calibrating these properties with physical testing. The model was subjected to a time history loading protocol involving five unique windstorms. After a month-long runtime, the simulation showed the building performed excellently with limited yielding in key elements.

After these tests, they concluded that ATX Tower is suitable for multiple reasons, including its shape and location. The slender, square shape of the tower produced a dynamic response due to wind vortex shedding, while the surrounding towers redirected wind, affecting ATX Tower. Additionally, test results revealed that wind loads from the east and northeast were 20-30% higher than building code estimates. Based on these results and to accommodate increased wind demands, MKA saw PBWD as an excellent alternative to increasing structural member sizes, leveraging their experience with Performance-Based Seismic Design (PBSD).

The next step of the project was to secure the approval of stakeholders. Once they ensured that stakeholders were on board, they hired a peer review team of wind and structural engineers to review the design, ensuring that occupant comfort predictions were within industry-standard limits without modifying the building massing or structural layout. They assessed the racking drift specific to exterior walls and internal partitions, which showed movements were within acceptable limits. Lastly, MKA demonstrated that they designed and verified the strength performance, using a 1.25 demand-to-capacity ratio for specific structural elements.

Last, alongside with PBWD, the team completed a parallel code-prescriptive design as a backup plan. Comparing both designs revealed several benefits of PBWD as 350 tons of reinforcing steel, 125 tons of structural steel, and 1,800 cubic yards of concrete were saved, they achieved a 5% reduction in the structure’s total cost, and they managed a 6% reduction in embodied carbon.

In all, ongoing research and advancements at universities and upcoming guidelines from the American Concrete Institute suggest a promising future for PBWD in building design.