Supporting an innovative green design with exceptional wind tunnel testing capabilities
The Nanjing Vertical Forest is a mixed-use complex that features extensive vegetation on a series of cantilevered terraces spanning the full height of its two towers. The structure adds visual interest and biodiversity to the city’s skyline while improving air quality and removing 25 tons of carbon from the atmosphere annually.
The project’s two towers – 200 meters and 108 meters in height respectively, and based on a shared podium – support an abundance of vegetation: a total of 1,100 trees from 23 local species, as well as 2,500 cascading plants and shrubs. These plants and the terraces that support them (the vision of the Milan-based architects Stefano Boeri Architetti and agronomist Laura Gatti) create unusual wind loading questions. The building’s structural engineers, ARUP, engaged us to help them study how the structure’s design would perform in its wind environment.
In addition to our team’s world-leading expertise in wind engineering, our large, state-of-the-science wind tunnels were important to this project’s success. To model the trees and terraces in enough detail to support effective analysis, we needed to model the building at a larger than normal scale (1:200). This meant that the building’s urban surroundings also had to be made larger – creating a risk of blockages in the tunnel and distorted results. A smaller wind tunnel with less sophisticated instrumentation would have struggled to meet this project’s requirements. Because helping innovators to push the boundaries of the possible is a long-standing part of our practice, we maintain infrastructure and equipment – both physical and digital – that can accommodate the world’s most demanding projects.
To ensure the safety and performance of the Nanjing Vertical Forest, we tested a number of configurations. We studied wind loads on the structure in its current surroundings, and in the built environment that’s expected to take shape around it in the coming years. We also studied the design with and without trees; this let us understand both the trees’ sheltering effects and any risks they might create in high winds (i.e. whether there was a chance they could be uprooted). To gain detailed insight into these complex structures, we fitted our models with multiple instrument types (both Irwin sensors and Cobra probes) – an unusual approach that proved highly effective. We worked closely with ARUP to ensure that our analysis met the rigorous requirements of the Chinese authorities who would ultimately review the project’s engineering.
The Nanjing Vertical Forest has earned all necessary approvals from Chinese building authorities, and is expected to be completed in 2018. It’s been hailed by the World Economic Forum and other entities as a promising example of biophilic design that has the potential to inspire other green building efforts – not only helping Chinese cities address the pollution that has accompanied their rapid economic development, but enhancing the sustainability, resilience and beauty of urban environments around the world.