Strategies to Reduce Lateral Forces on High-rise Buildings that Use Diagrid Structural System

Figure 2. Millennium Tower

Figure 3. Model of Jin Mao Building

                        Phage 2

C) Tapering and Setbacks
Reducing floor areas gradually toward the top is a good strategy to enhance lateral performance of a building. This way, the mass of the building is concentrated in the lower floors. More importantly, when hitting a building using tapering and setbacks, the vortices will try to shed at different

frequencies at different heights. In other words, the winds become “confused” and incoherent, which can dramatically reduce the associated fluctuating forces Examples of “tapering” strategy are: John Hancock Center (Chicago), Millennium Tower (Tokyo), and Transamerica Pyramid (San Francisco). The Jin Mao Building (Shanghai) and the Petronas Tower (Kuala Lumpur) are good examples of using “setbacks” to slightly taper the building shape.While “setback” is rather tricky to apply to a Diagrid building because of the continuity of the structure, “tapering” is highly suitable.

D) Sculptured Building Tops
The sculptured building tops not only highlight the height of the structure, but also serve the practical aerodynamic purposes such as reduction in the wind response of the building. The more sculptured a building’s top, the better it can the along wind and across wind responses. Examples: Jin Mao Building, Petronas Towers, etc.

Figure 4. 30 St Mary building uses
“spoilers” to defect wind loads

Figure 5. Shanghai World
Financial Center

E) Varying Cross-section Shape
Varying cross-section shape with height, e.g. going from square to round, can force the wind to behave differently, preventing in becoming “organised”. This results in “confused” vortices, which is a similar effect to using tapering and setback. Examples include Buji Khalifa (Dubai) and the Sears
Tower (Chicago).

F) Rotated and Twisted Forms
Rotated building forms can minimize loads from prevailing directions, while twisted forms can avoid simultaneous vortex shedding along building’s height.

G) “Spoilers”
Vortex shedding can also be reduced by adding “spoilers” to the outside of the building. The most well-known form of spoilers is the spiral Scruton strake which is widely used on circular chimney stacks. It is very convenient to use this strategy on Diagrid structures due to the geometry benefit of
the grid. Example: 30 St Mary building (London).

H) “Through-building” Openings
In sustainable design of tall buildings, opening areas are fundamental. This can be exploited to provide areas whichwind can blow all the way through, thus reduce wind loads.
Diagrid, with its unique structure characteristic, can provide random openings without affecting the structure at all. Multiopenings is also a good strategy. Example: Shanghai World Financial Center (Shanghai).