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

                                                               Phage 3

STRUCTURAL REINFORCEMENTS
Without going too deep into the technical aspects, basically, structural reinforcement strategies that can be applied to highrise Diagrid structures include:
- Super-columns addition: Adding super columns or sets of columns to strategic locations of a Diagrid structure – Fig. 6a.
- Coupled buildings: 2 or more buildings are linked together for better structural performance - Fig. 6b. The Petronas Towers are a typical example of this approach.
- Core and Outrigger support: Adding a core and outriggers to the Diagrid structural shell – Fig. 6c.

Figure 6. Structural reinforcement strategies

1) Energy-dissipating-material-based damping systems are generally installed as integral parts of primary structural systems at strategic points, reducing the dynamic motion of tall buildings. The damping force in a viscous damper or visco-elastic damper is dependent upon the time rate of change of the deformation. Damping is accomplished through the phase shift between the force and displacement. An example of viscous dampers, installed as an integral part of the bracing members, can be found in the 55-story Torre Mayor in Mexico City – the tallest building in Latin America at present, and visco-elastic dampers were installed in the destroyed World Trade Center Towers in New York. Other types of damping systems in which the damping mechanism is through direct dissipation of energy from the system include hysteretic damping and friction damping. Fig. 8 presents an example of a viscous dampers system applied to a Diagrid high-rise building.

Figure 7. Types of Auxiliary Damping Devices/Systems

Figure 8. Example of a viscous dampers system applied to a Diagrid structure

2) A TMD is composed of a counteracting-inertia-forcegenerating huge mass accompanying relatively complicated mechanical devices that allow and support the intended performance of the mass. The frequency of the TMD mass is generally tuned to the fundamental frequency of the primary structure. Thus, when the fundamental mode of the primary structure is excited, the TMD mass oscillates out of phase with the primary structure, generating counteracting inertia force. Fig. 9 shows different types of TMD. A TMD system, located near the top of the building for its best performance, is installed in a room that is usually not accessible to the public, as in the cases of the sliding type TMDs installed in the John Hancock Building in Boston and the Citicorp Building in New York. However, the pendulumtype TMD installed in the Taipei 101 Tower is used as a decorative element in the building interior as well, attracting interest of visitors – Fig. 10.

Figure 9. Different types of TMD

Figure 10. Taipei 101 Tower’s TMD system

Figure 11. Different types of TLD

3) TLD, such as tuned sloshing dampers (TSD), use waving water mass as a counteracting inertia force generator. Thus, this system can be designed using the existing water source in tall buildings, such as a pool or water tank located near the top of a building. In a TSD, sloshing frequencies are tuned by adjusting the dimensions of the water container and the depth of water. Another type of TLD is tuned liquid column dampers (TLCD), which uses a U-shaped vessel. Fig. 11 shows different types of TLD.