Council on Tall Buildings and Urban Habitat
 

YPC Event on Resisting Wind: Performace and Behavior of Tall Buildings for Wind Loads
January 13, 2016
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NEW YORK CITY – On January 13th, the Langan New York City office along with CTBUH New York City and the CTBUH NYC Young Professionals Committee (YPC) welcomed over 80 design professionals for a presentation on wind engineering and understanding its effects on tall buildings. The event kicked off with an introduction to CTBUH by YPC Co-Chair Hardik Doshi, Structural Design Engineer, McNamara Salvia. Hardik summarized notable past CTBUH activities such as the 2015 Conference and introduced the local chapter’s plans for 2016.
The intent of the presentation was driven from the YPC members’ keen interest to learn more about the effects of wind on tall buildings. The presenters, Anton Davies, Founding Partner, at RWDI, and Alan Poeppel, Senior Principal, Langan, described their expertise on this subject. A common topic of discussion was Jeddah Tower, the future world’s tallest building. Having worked on Jeddah Tower, both Davies and Poeppel had fascinating thoughts to share from their design experiences. 
 Tuned Mass Damper illustration
Davies discussed the wind engineering efforts used to facilitate the design of tall buildings, and also provided some insight into the design of shorter buildings such as those found as part of Masdar City. On the tall tower side, the initial focus was on Jeddah Tower and wind’s effect on the design. The tower will be slightly over 1,000 meters in height. It was designed by architect Adrian Smith of Adrian Smith + Gordon Gill Architecture, and the structural engineering was undertaken by Bob Sinn of Thornton Tomasetti. RWDI provided the wind loading results that would be needed to define the strength of the structural system, as well as a measure of the acceleration rates at the top occupied floor. These latter numbers are important because they define the anticipated level of comfort that would be experienced by the occupants of the building 
Anton Davies, Founding Partner, RWDI discusses the wind engineering efforts in the design of Tall Buildings.
In the case of Jeddah Tower, the well-defined shape of the building had the effect of minimizing the vortex shedding influences on the crosswind loading of the building, such that the acceleration rates were in line with what would be needed to ensure occupant comfort. However, in the upper part of the tower, where there is a 300 meter high spire, it became clear that the tip displacement of the spire was such that additional stiffness and/or damping would be required to minimize the effect of fatigue. To this end, two tuned mass dampers have to be employed in the upper-most part of the structure.

Following the addition of this added damping mechanism, the displacements are anticipated to be well within the levels required to ensure longevity of the spire and to minimize the acceleration rates in the upper building in the event that workers have to occupy that space during a wind event. To help the audience appreciate the methodologies required to come up with the design information needed by the structural engineer and the architect, the presentation provided images of scale models of various projects, including 432 Park Avenue in New York, Burj Khalifa in Dubai, and Taipei 101.

The second part of Davies’ presentation had to do with sustainable design. In particular, RWDI was retained as the sustainability consultants for Masdar City. Working in conjunction with Foster + Partners, this net-zero carbon city took shape.  The key performance indicators for this development required that a minimum amount of energy would be used to operate the city. Davies discussed the design elements of Masdar City in detail. In particular, he discussed the passive design strategies used to foster a cooler environment without energy consumption. These strategies included self-shading buildings and streetscapes designed to allow sea breezes to penetrate deep into the core of the city with the help of wind towers. He argued that Masdar City was an example of going well beyond LEED Platinum, and concluded by noting that the principles used in the development have been confirmed and tested.
 
Wind Tower Analysis Model                                                             Wind Tower in Masdar City

Alan Poeppel’s presentation focused on the foundation analysis and design for supertall buildings. Because of the overall size and weight of these buildings, the subsurface investigation requires extensive field exploration, including borings that extend 150 meters or more into the ground, in-situ physical and geophysical testing, and a wide array of laboratory testing.

The purpose of these investigations is to determine the types of soil and rock materials at the tower site as well as the physical and engineering properties of these materials. The foundation design focuses first on the overall bearing capacity of the concrete foundation raft and, if needed, the supporting deep pile elements.  However, with supertall buildings, engineers are more often faced with the challenge of the overall settlement of the structure.  Here the performance of the foundations must be compatible with the building’s superstructure.  Too much settlement can create unplanned and unwanted changes in the load paths through the superstructure.  Conversely, overly conservative foundation design can lead to significant cost and schedule impacts that could ultimately scuttle the project.  

Finally, as Poeppel described, the foundation design is validated through full scale field load testing, proper quality control during construction, and structural health monitoring of the foundation during tower construction and throughout building use.  

The more than hour and a half long presentations were followed by a group discussion and questions from the audience. CTBUH would like to thank Langan for hosting and sponsoring the lively networking session before the presentations at their New York City office.

The event was organized by YPC Co-Chairs Ilkay Can-Standard, Architectural Designer, KPF, and Hardik Doshi, Structural Engineer, McNamara Salvia, with help from YPC Steering Committee Members Larry Giannechini, Senior Engineer, Thornton Tomasetti, and Elizabeth Geldres, Architect, Rafael Viñoly Architects.