Celebrating the release of the “Outrigger Design for High-Rise Buildings” at the CTBUH World Congress in Shanghai are (from left) Anthony Wood, CTBUH executive director; David Scott, Laing O’Rourke; Ryan Chung, Dongyan Structural Engineers; Nabih Youssef, Nabih Youssef Associates; Mark Sarkisian, SOM; Senior Principal Hi Sun Choi; Charles Besjak, SOM; Outrigger Working Group Co-Chair Goman Ho, Arup; Ron Klemencic, Magnusson Klemencic Associates; Steven Henry, CTBUH; and Vice President Paul Fu. Photo courtesy of CTBUH.
Hot off the press and available in all Thornton Tomasetti offices is the Council on Tall Buildings and Urban Habitat’s “Outrigger Design for High-Rise Buildings“. The technical guide, the first-ever for outrigger systems, was developed with considerable input from our engineers and features many Thornton Tomasetti-designed supertalls as examples.
The publication, which offers an overview of various outrigger systems applications, design considerations and recommendations, has been added to the library at each Thornton Tomasetti location. “The guidelines are not available in an electronic format,” New York Senior Principal Hi Sun Choi, who along with Los Angeles Principal Len Joseph were among the guide’s principal authors, said. “We purchased one hundred copies to assure access for all our staff through office libraries. If people need additional copies for clients we can provide them.”
Some two years in the making, the guidelines were drafted by CTBUH’s Outrigger Design Working Group, co-chaired by Choi, Joseph, Neville John Mathias of Skidmore, Owings & Merrill LLP and Goman Wai-Ming Ho of Arup Group. Significant contributors to the document included Chicago Principal Bob Sinn and New York Associate Cori Kwitkin. They also served on the peer review panel, along with Vice Chairman Aine Brazil, Principal Eli Gottlieb, Vice President Paul Fu and Associate Simon Shim, all of the New York office.
“Outrigger systems are nothing new, but specific design guidelines for them had not been previously available,” Choi said. “In our firm, which has considerable experience designing outrigger systems, we have established best practices that we follow. But smaller firms and less experienced engineers might not know how to approach outriggers. These guidelines detail the advantages and disadvantages of the different types of systems as well as the various design considerations.”
Although we have a wealth of in-house expertise designing outrigger systems, including the New York Times Building and Taipei 101, which are examples in the guide, the publication can serve as an important resource for our staff. It can be a refresher for the practical aspects of designing and detailing outrigger systems as well as a reference guide for understanding the key aspects and potential challenges.
“When you suggest an outrigger system to a client, you need to be able to explain what the pros and cons are,” Joseph said. “The smarter we are in the early concept stages, the better we can help the project team reach the appropriate solutions.” In addition, the guide can be used to show clients and contacts Thornton Tomasetti’s leadership in high-rise building design,” he said.
Building examples also highlight alternative approaches to outrigger design, including outrigger-driven damping and outriggers of buckling restraint bracing members, which Thornton Tomasetti designers have not employed before. “Our engineers need to understand what others in our industry are doing,” Choi said. “We designed outriggers based on our own experience, and it is important to gain exposure to alternative methods so we can be ready to take the next step.”
While Choi and Joseph are pleased with the guidelines, they say it is only the beginning. “We have created the platform,” Choi said. “While I don’t think the basic principles will change much, there is room for additional clarifications and comments as well as new innovative ideas.” For instance, at a meeting of the Outrigger Working Group prior to the CTBUH Shanghai World Congress in September, attendees suggested adding guidance on appropriate outrigger types and design parameters for outriggers in different conditions, such as wind-controlled and low, moderate and severe earthquake conditions.
“One of the implicit goals of the guideline document was to trigger further discussion,” Joseph said. “And it is already starting to do just that.”
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