High Performance Structures with Viscous Dampers

The structural solution developed for NASA in the 1960s, is an outstanding example of civil engineering today.

Earthquake-Resiliency with Viscous Dampers

Originally developed for NASA in the 1960s, fluid viscous dampers have successfully transitioned into the civil engineering applications in the last three decades. Adding damping to buildings can be used for a variety of applications including seismic events, strong winds, and pedestrian energy in protecting buildings, bridges and other structures.

  • FVDs provide uninterrupted use after an earthquake and increase business sustainability.
  • Protects non-structural elements from earthquakes as it reduces floor accelerations and dampens shock and vibration.
  • It is used to reduce force and deformation demands below the existing structural capacity and reduce the need for costly retrofitting.
  • It works even under the smallest influences, regardless of a specific earthquake/wind force threshold level.
  • It provides the ideal solution for the protection of “High-Rise Buildings” that are sensitive to high-period long-distance earthquakes.
  • Unlike all other dampers, the permanent displacement in the structure is zero as it returns to its previous position after the earthquake.

High-Rise Damper Applications

The use of energy dissipating devices to reduce building response from dynamic inputs has become an accepted design approach for high rise buildings. New approaches are continually being developed by designers as evidenced by the varied applications of viscous dampers, tuned mass dampers, and visco-elastic dampers. These damping solutions can be added to new buildings or used as seismic retrofits to existing buildings. Each of these building damper systems has its own idiosyncrasy and the optimal solution must be evaluated for the particular project under consideration. Read more about each solution below.

Damped Megabrace System

A novel strategy for dynamic control of high-rise towers is the damped megabrace system. The system provides damping within the length of megabraces that span multiple floors. The damped megabrace works by placing a fluid viscous damper or a group of dampers at the end of a long bracing element which forms the main lateral resisting system. Since the viscous dampers provide no resistance to static loading, a parallel system of bracing is also used.

Benefits:

  • Fewer dampers in the structure.
  • Less steel, reducing cost & improving performance.
  • Reduced weight is advantageous in areas where soft soil – conditions and liquefaction are a concern.
  • Damping can be integrated as an architectural feature of a building.

Damped Outrigger Systems

A damped outrigger system is highly efficient in reducing dynamic movements from hazardous winds. This system is based on the concept of total gross movement of the structure, applying vertical tension/compression forces into perimeter columns. Outrigger damping can be accomplished by constructing a rigid cantilever off the core of the building within a specific floor level, or levels, and connecting fluid viscous dampers between the end of the cantilever and the outer columns. The solution takes advantage of the tension and compression on the opposing outer columns of the building which amplifies the movements of the central core at the location of the outriggers.

Benefits:

  • No temperature sensitive viscoelastic materials.
  • No failure prone components like valves.
  • No need for re-centering, repair or replacement.
  • Provides energy dissipation to all frequencies of input vibration.
  • Components are small and can be hidden in various locations throughout the structure.
  • Avoids large potentially dangerous masses in the structure.
  • Can be used to reduce service and strength level demands.

Tuned Mass Dampers

Tuned mass dampers (TMDs) are attached to high-rise towers to reduce dynamic response caused by hazardous winds. A TMD is a system composed of a mass, springs and dampers tuned to a specific frequency. The amplitude and frequency of sway depends on height, slenderness and rigidity of the structure. In high-rise buildings, such sway may make people uncomfortable at low frequencies. When a frequency of wind loading causes dynamic amplification of a tower, the TMD will resonate out of phase with the building, energy will be dissipated by the dampers, and the tower’s dynamic response is improved.

TMDs have been successfully added to various structures throughout the world. Structures such as bridges, skyscrapers, staircases, stacks, and antennas can all be excited to high levels of vibration from wind, earthquakes, nearby machines, or traffic. All of these structures require TMD systems to eliminate discomfort, damage, or outright structural failure caused by vibration in the structure. Fuji Engineering manufactures viscous damping devices for large scale TMD systems as well as full custom TMD systems for pedestrian bridges, walkways, concert venues, as well as other structures.

They do not depend on external power source for their operation.

  • They can respond to small levels of excitation.
  • Their properties can be adjusted in the field.
  • They can also be introduced in structural upgrades or retrofits.
  • They require low maintenance.

Direct Acting Damping

It is common practice today that structural engineers do not design their structures to remain fully elastic during a seismic event as in the past. Instead, they allow structures to experience plastic hinging (damage) in certain areas that are carefully detailed for this particular reason. Energy dissipation is achieved through hysteretic damping at these plastic hinges. This concept of ductile design leads in general to more economical designs provided that a certain level of safety is still maintained. Whether the goal is to reduce wind or seismic energy, there are a variety of solutions for energy dissipation for safer and more cost-effective structures in the long run.
While many methods exist to implement distributed damping in a structure, the underlying concept is to connect the dampers where motion will occur, such as between beam and column joints or between floor levels which deform relative to one another in a shearing-type motion. Some common configurations are listed below.

Open Space
While not specifically used for high-rise buildings, Taylor Devices does offer an open space configuration designed to offer more open bays.

Toggle
Toggle frames can be used as a mechanism to amplify deflections into the damper in otherwise stiff, or tiny deflection situations, creating a more efficient damping system. Toggle Frames utilize a bent-brace mechanism theory to capture deflections in one plane and translate the deflections into another plane and therefore provide very efficient damping.

Chevron
In this configuration, the dampers are placed horizontally, and connected to a frame (chevron) that is intended to be near-rigid with the floor it is connected to. The advantage with this direct damping orientation is that the horizontal flexibility of the structure injects this full movement directly into the horizontal orientation of the damper. However, a small amount of motion can be lost due to the constraints of the attainable stiffness of an economical chevron frame.

Diagonal
A very common method of applying distributed damping to a structure is to connect the dampers to diagonal corners or center of a structural frame or bay. In this orientation, the horizontal movement of the structure allows an angular component of the full deflection to go into the damper. This takes the motion directly to the next floor level through a strong tension/compression member.

Bridge Damper Applications

When it comes to bridges that are subjected to seismic, wind, or traffic inputs, engineers must decide how to reduce or eliminate lateral motion and feedback. One potential solution is changing the frequency, or period, by stiffening the bridge through additional bracing or piers. However, when going this route, a substantial amount of structural modifications may be required leading to an increase in weight of the bridge and substantial costs. Additionally, this can also affect the unique architecture of the bridge.

Another solution is to add a direct acting damping system to the bridge to reduce resonant deflections to a low level. This system can increase damping levels from the usual 0.5%-1% critical damping to a 20% critical damping range. Our fluid viscous dampers have the unique ability to simultaneously reduce both stress and deflection within a structure subjected to a transient vibration. This is because a fluid viscous damper varies its force only with velocity, which provides a response that is inherently out-of-phase with stresses due to flexing of the structure.

Direct Acting Damping for Bridges

Similar to systems found in buildings, direct acting damping can be used in bridge applications to absorb wind, seismic, and pedestrian energy. Fluid viscous dampers are installed to provide damping into the system and, consequently, reduce force and displacement demands. A reduction or even elimination of structural damage as well as traffic loss could be achieved after a seismic event, yielding substantial economic benefits.

Lock-Up Devices for Bridges

Lock-Up Devices (LUDs) are a component from the same general technology base of fluid dampers, but unlike a fluid damper, the LUD does not dissipate energy. Rather, the LUD effectively acts as a dynamic brace to literally “lock” multiple masses together under seismic, wind transients, temperature expansion and braking effects. When equipped with Lock-Up Devices, a multiple mass structure essentially acts like a single, monolithic mass when a transient event occurs.

Tuned Mass Dampers for Bridges and Long Span Floors

Similar to systems used in high rise buildings, tuned mass dampers (TMDs) for bridges will resonate out of phase with the bridge creating an opposing forcing function so energy can be dissipated by the dampers, and the bridge’s dynamic response is thereby improved. The only difference is that these TMDs are built at a much smaller scale, for much smaller input – typically pedestrian synchronized events.

Modern pedestrian bridges are sometimes long and slender in form, usually leading to a structural design with relatively low frequency primary modes of vibration. Similarly, some convention centers, hotels, concert halls and/or theaters are built with very long spans. Because of this, the bridge or floor can easily be excited by synchronized activities such as jumping, dancing, or even something as simple as walking. Unlike fluid dampers which convert mechanical energy into thermal energy, a tuned mass damper system will create a forcing function to oppose the induced dynamic structural deflection, thus suppressing motion.

Generally, TMDs are considered effective in applications of controlling structural motion where direct damping cannot be applied.  TMDs can be effective in the single frequency that they are tuned to, for controlling motions induced by wind, crowds of people, or other low-level vibration, where damping levels of less than 10% can be used. Multiple TMDs can be used if several modes can be excited by the input causing vibration.

Fuji Engineering manufactures large scale as well as full custom TMD systems for pedestrian bridges, walkways, concert venues, as well as other structures.

Low/Mid Rise Building Damper Solutions

When living in an area that is prone to earthquakes, extensive means must be taken in order to preserve structural integrity. Current building codes only require that a building should not collapse during a major earthquake, however, heavy structural damage is acceptable under the current building codes, even irreparable structural damage. We have a variety of building damper solutions that absorb energy of an earthquake, so the building doesn’t have to. Our dampers are maintenance-free and designed to reduce stress, deflection, and acceleration, protecting the structure and content.

How Viscous Dampers Can Improve a Base Isolation System

Visous dampers can also be included in a base isolation system where the damper is used to augment the energy dissipation of the isolators. The reduction in dynamic displacement provided by the addition of the viscous dampers can reduce the required size of the base isolation system by decreasing the cost of the bearings, moat covers, utilities entering the building, and other items that increase in cost as displacement increase. This reduction to the system components make it less costly and more practical to design and build. It is not uncommon to find that a combination of Dampers and base isolators, when optimized for performance, is less costly than the isolators would have been without the dampers. Another benefit of using dampers with the base isolation system is for when space is limited. By reducing the displacement of the base isolation system, the result is more usable space since the perimeter of the building can be closer to the property

Viscous Dampers for Base Isolation

Base isolation systems reduce structural excitation by physically decoupling the structure from the ground. This type of solution requires that the entire structure be cut loose and separated from the foundation system and isolation pads inserted in between the two. By doing so, the building will be isolated from the movement of the ground during seismic events and can achieve 6 degrees of freedom.

Corporate News

Any Questions?

Do you have questions about our systems and solutions?

Contact Us
Scroll to Top