An irregular, wedge-shaped TSD tank was used in this project in China, as shown during construction (left) and from the inside before water was poured (middle). At right is the TSD schematic design. Many TSDs usually have concrete walls and floor and roof slabs; however, on this particular project, the client requested an all-steel tank.
the system should also be included in the simulations. The result is a sufficiently robust design that will provide a steady level of supplemental damping across a wide range of as-built conditions for the tall building. Full scale measurements are performed once the TMD is installed and tuned to demonstrate that the TMD performs as designed. One downside of a simple pendulum system is that it could necessitate a very tall room due to the cable length requirement. For example, a tall building with a 6-second period requires approximately 30 feet of cable length—equivalent to about three stories. To account for variability in building frequency, this cable length may need to be increased to approximately 36 feet—equivalent to almost four stories tall. A solution has been developed and successfully implemented to resolve this issue: the use of an opposed-pendulum type of system. One example of this is the 111 West 57th TMD in New York City; some details of this TMD have been presented in a New York Times article. An opposed-pendulum TMD consists of a simple pendulum system attached to an inverted pendulum (a secondary mass suspended from the floor via steel columns). The TMD frequency is determined by proper configuration of the ratio between the two masses and the cable length and column height. For the 111 West 57th TMD, the required height of the TMD room would have increased four-fold had a simple pendulum TMD been implemented. While opposed pendulum systems require the least amount of space, they do require slightly more engineering and higher costs. If space is not as much of a concern, especially if the required supplemental damping and therefore damper mass is not too high, TLD systems may be considered. However, only 60% to 80% of the water in TLD tanks actually participates as dynamic mass within the mass damper system. On one project, a 1000-ton TMD was required, but the client opted for a less expensive TSD alternative that, in the end, held nearly 2,000 tons of water! On one project in Australia though, where the damper mass requirement was only in the order of approximately 200 tons, a TSD was the perfect solution for the client. An earlier consultant recommended a three-tank TLCD system, but by using performance-based design principles, constant coordination with the client, and full-scale building frequency measurements during construction, the project ended up employing just a one-tank TSD system that allowed the client to introduce a new penthouse apartment unit that more than made up for the cost of the TSD implementation. One key factor in the success of such a TSD design is that the water TSD tank was incorporated into the fire suppression water storage system. In short, the tank served dual purposes: as a TSD and as fire suppression water storage. During 14 STRUCTURE magazine
commissioning of the TSD system, full scale measurements were done and analysis of the data reveal that the TSD is performing as expected. However, not all projects can accommodate a rectangular, box-shaped TSD tank. Again, as part of a performance-based design approach, coordination with clients reveals that only an irregular shaped tank can be accommodated in some projects. The numerical modelling used in the performance-based analysis and design of TSDs is verified using data collected from scale-model testing in the laboratory. For irregular tanks, the same approach is used. One project in China has used a triangular, wedge-shaped tank. Certain types of spire-like structures on buildings or on-ground have used annular-shaped (i.e. “donut-shaped”) tanks. On one super tall building in New York City, the building could only accommodate a tank that wrapped around the concrete core— effectively requiring a “square bagel”-shaped tank (i.e. a rectangle with a smaller rectangle cutout in the middle). By employing a performance-based design approach, it is possible to employ a wide variety of tank shapes that can still achieve the performance objectives.
Summary and Conclusion Various damping technologies are available that provide a reliable level of damping, meet performance requirements, and fit within the project’s space constraints. Successful examples of TMD and TSD systems for wind response control have been implemented in tall building projects across the globe, where performance-based design principles were used and in-situ performance verification has been demonstrated.■
Full references are included in the online version of the article at STRUCTUREmag.org. Ron Aquino is a Senior Engineer for Applied Structural Dynamics with Motioneering, Inc. in Guelph, Ontario, Canada. He is a licensed professional engineer in Ontario, Canada and in the Philippines. Shayne Love is a Technical Director for Applied Structural Dynamics, also with Motioneering, Inc. He is a licensed professional engineer in Ontario, Canada and in Michigan, USA. Jamieson Robinson is a Vice President for Operations, also with Motioneering, Inc. He is a licensed professional engineer in Ontario, Canada.