The inline friction damper dissipates energy as the elements of the damper slide relative to one another in both tension and compression, converting an earthquake’s kinetic energy directly into thermal energy in a non destructive process. For a quick example, rub your hands together and you’ve just transformed a force through a distance (energy) into heat.

Benefits of Inline Friction Dampers

• Low cost of device and installation
• Allows for reduction in size of structural sections
• Easy to design with, not velocity or temperature dependent
• Rectangular hysteretic loop, highest (maximum) energy dissipation per cycle
• Maintenance free
• Can be installed in parallel to develop large loads
• Acts as a load limiting device (slip load limits buckling, column and foundation loads)

Installation Configurations

• Single diagonal
• Parallel (for larger loads)
• Chevron (at the top or in the diagonals)
• At beam/column connections
• Toggle
• Bolted, pinned or welded

A Rotational Friction Damper dissipates seismic energy by friction generated through a rotating friction joint, with constant torque. The force in the connected braces is dependent on the angle to overcome the slip force in the friction joint. The component of the force in the brace, normal to the link multiplied by the length of the link must be equal or greater than the constant torque to slip. This type of damper can be modeled with a rectangular hysteretic loop for small displacements (changes in angle between the damper links).

Rotational Friction Dampers have been used since the early 1900s in vehicle suspensions and represent a robust technology for use in seismic force resisting systems for structures. Although this is a well proven technology there is more variation in the force due to changes in angle as well as variance in individual dampers due to manufacturing tolerances, it therefore remains important to conduct 100% testing of the rotational friction dampers before use in seismic applications.

A Rotational Friction Damper dissipates seismic energy by friction generated through a rotating friction joint, with constant torque. The force in the connected braces is dependent on the angle to overcome the slip force in the friction joint. The component of the force in the brace, normal to the link multiplied by the length of the link must be equal or greater than the constant torque to slip. This type of damper can be modeled with a rectangular hysteretic loop for small displacements (changes in angle between the damper links).

Rotational Friction Dampers have been used since the early 1900s in vehicle suspensions and represent a robust technology for use in seismic force resisting systems for structures. Although this is a well proven technology there is more variation in the force due to changes in angle as well as variance in individual dampers due to manufacturing tolerances, it therefore remains important to conduct 100% testing of the rotational friction dampers before use in seismic applications.

For small building drifts, a rotational friction damper can be assumed to have a rectangular hysteretic loop which make analysis and design simple and straightforward. For larger drifts (rotations in the damper links) more over strength in the connections will be needed and the hysteretic loop should be explicitly modelled as trapezoidal in a nonlinear analysis. This effect is illustrated in the characteristic trapezoidal loop (bottom left) of a single rotational friction damper or the parallelogram shaped loop (bottom right) of the x-brace rotational damper. Depending on the aspect ratio and requirements of the specific frame the variations can be reduced. In cases where the force variations must be minimized (e.g. most retrofits) you can refer to our Linear Friction Dampers.

It may seem surprising that dampers tend to reduce the cost of structures. Achieving a given seismic performance using dampers tends to be less expensive (depending on the cost of the dampers) than if you were trying to do so by using brute force stiffening methods alone (Shear walls, stiff braces etc.). Friction dampers tend to be less costly than other dissipation technologies because of their highly efficient rectangular hysteretic loop (less dampers required), their full integration into the lateral resisting system and their low per unit cost. It’s very common to find examples where axial and shear forces in columns are reduced by 40% to 60% of those found in other methods of seismic protection and retrofitting (Vezina, S., Proulx,P., Pall, R., and Pall, A., 1992 and Balazic, J., Guruswamy, G., Elliot, J., Pall, R., Pall, A., 2000). With this kind of reduction in the elements’ forces, elements can be better optimized and structural costs tend to be substantially reduced. It’s not uncommon to see cost reductions of up to 60% in retrofitting and to 10% in New structures.

From a lifecycle perspective, ductile technologies (yielding connectors, BRBs etc) tend to pose another challenge, in that they require replacement after an earthquake. This is of course preferable to damage of other elements, such as columns or beams, but very costly in a finished building where operations have to be disrupted to replace the ductile element. Since friction dampers don’t require replacement after an earthquake there are also significant lifecycle cost savings.

Traditional methods while safe when well designed, tend to actually be more expensive because of their lack of energy dissipation causing oversized sections or usage of ductility limiting usage after an earthquake. Integrating energy dissipation reduces the forces on the members allowing for more efficient structures which are ultimately less expensive.

Simply storing the earthquake energy and relying on the small amount of entropy to dissipate it is inefficient. When an earthquake that exceeds expectations occurs it’s easier to exceed the building’s capacity when there is little dissipation.

To try and store all the earthquake’s energy is ultimately impractical and leads to overly stiff and heavy structures with larger accelerations (forces).  Using seismic dampers can reduce lateral displacements without causing higher accelerations. This in turn helps to achieve the same seismic performance with a more efficient (lighter) structure, bringing costs benefits to the final client. In several examples, (Vezina, S., Proulx,P., Pall, R., and Pall, A., 1992, Chandra, R., Mas and, M., Nandi, S., Tripathi, C., Pall, R., Pall, A., 2000), we see how traditional alternatives based on structural steel and reinforced concrete tend to make the structures stiffer, but at the same time, bring the problem of increasing input energy (higher mass, same ground motion). This usually carries the problem of inevitable strengthening of structural elements and foundations.

With dissipation technologies providing overall cost savings and being as easy to use as they are today, there is no reason not to integrate them and achieve better performance.

Friction dampers are meant to be maintenance free and slip during design earthquakes or higher. Cases where the dampers would slip daily for example would be inappropriate.

Dissipating wind energy would be an example of an inappropriate use. Displacements due to wind should fall within the range of stiffness of the building before damper activation. The dampers are often used when there are strong wind loads however the slip load is recommended to be approximately 1.3times the expected wind load. In tall structures, this has the added benefit of reducing displacement due to wind which can cause discomfort to occupants.

The intended use of the friction damper is for reducing or eliminating earthquake damage due to design (DBE) and maximum considered (MCE) earthquakes.

Friction dampers for dissipating wind energy
Friction dampers can be designed to slip under wind forces using high wearing composite friction pads and Belleville washers (spring washers) to make up the wearing. However such a design would involve replacing or reworking the dampers periodically due this wear of the interface and fatigue of the springs. So, although feasible and possible, the periodic maintenance implication would make it costly.

Therefore, viscous dampers tend to be a more appropriate technology for dissipating small amounts of energy such as wind.

Stick Slip is a common phenomenon which can be observed (usually heard) in everything from hydraulic cylinders, brakes and even in fault lines! Stick-slip is responsible for the screeching of brakes or the sound produced by many musical instruments. A damper experiencing stick slip will be quite loud and screech or squeal. The effect is especially prominent in bi-metallic dampers, steel on steel or poorly manufactured interfaces.

Quaketek’s friction dampers do not exhibit stick-slip characteristics and are quiet throughout their entire travel at full load.
Each damper is individually tested at load and for the full stroke to ensure that the load remains constant and that there is no sign of stick-slip or other non-desirable characteristics. The damper remains quiet throughout its entire travel and the noise generated by the damper tends to be less than 60db.

We use high-strength structural bolts in our seismic dampers which have been extensively studied and documented. Their behavior is well understood and have been used in structural connections for more than 60 years. Studies supporting AISC bolt design guidelines, Tajima (1964), Chesson and Munse (1965), and Allan and Fisher (1968), have found that bolt relaxation occurs in the highest proportion just after bolt pre-tensioning. Usually, total variation is on average 8% over an 80-90-year period. Around 80% (6.5%) of this 8% drop occurs within one week of the initial pre-tensioning. We, therefore, account for this bolt relaxation in the initial calibration of the dampers.

Studies have shown that changes of up to ±25% from the optimal slip load do not considerably affect the structural response. Small changes in the slip load due to relaxation will, therefore, have minimal effect.

Additional considerations on bolt relaxation
High wearing or soft interfaces worsens bolt relaxation in the connection, this creep could be made up for with Belleville washers. Thick Belleville washers, however, are themselves prone to creep and fatigue failure over time due to high stress at the edges (ASTM, Journal of Testing and Evaluation vol 42). Therefore, in Quaketek friction dampers, creep/wear-prone elements are avoided in the friction interface altogether.

A friction damper which is essentially a coulomb damper transfers the energy directly into the surfaces which dissipate the heat through the entire damper mostly through conductive heat transfer. The amount of temperature change will ultimately depend on the thermal mass of the damper and conductivity of its elements.  If the damper has insufficient thermal mass or poor conduction it will heat up excessively.

In our case, we have carefully developed the friction interfaces to ensure conductive heat transfer, minimal thermal expansion and corrosion resistance. This is important because certain materials will actually become velocity dependent as they heat up. For example, friction sliding isolation bearings will sometimes use composites or PTFE which is a polymer (plastic). As plastics approach their glass transition temperatures they behave more similarly to fluids. This abrupt change in the behavior of plastics creates challenges in modelling and predictability of the elements’ performance. Further complicating the use of plastics in friction interfaces is poor heat conduction. Since friction dampers convert earthquake energy into heat it’s important that the heat be conducted away from the friction interface quickly, which is not the case with plastics and many other materials resulting in excessive heat generation especially at high velocities.

Therefore, when it comes to friction seismic dampers is better to have bigger friction surfaces and thus, bigger mass.

Quaketek has developed frictional surfaces that are protected against corrosion and that undergo and extremely small amount of wear even after many cycles. Friction dampers must be carefully designed to avoid changes in slip load over the life of the building.

Older generations of friction dampers used brass plates against steel plates to ensure a connection with low creep however these kinds of connections could suffer from galvanic corrosion in the long term. This concern lead to provisions in some building codes prohibiting bi-metallic interfaces (FEMA P-1050-1, 2015).

Using technologies originally developed for Aerospace, the Quaketek friction damper uses a low wearing hard interface which has been protected against galvanic and other forms of corrosion, while maintaining low wear and very little creep. The end result, is a friction damper that generates a stable slip force throughout the lifetime of the building.

Every Quaketek friction damper has been tested at the full slip load and full stroke. Part of our production process is a 100% test of every batch. The customer can be confident that the damper will slip at the expected load because we have tested every single one. This testing is not required by the majority of building codes (although the latest Chilean code, NCH3411 now requires it) however it would be irresponsible not to. The founders of Quaketek have been building friction dampers since 1987 and one thing is clear: no matter how consistent your manufacturing process, coupon tests or sample checks, only 100% full scale production testing will ensure accurate calibration and repeatability of performance.

In addition to our 100% production test we invite customers or their engineers to be present during our final inspection and test before shipment from our Canadian manufacturing plant. We are confident in the durability of our dampers and are happy to offer customers the option to schedule periodic tests on them at 10 year intervals.

Structural engineers selecting Quaketek dampers can be 100% confident that they are receiving a quality damper that will behave as expected when an earthquake strikes.  The end result is 100% confidence in our product backed by our guarantee.

This will depend on the performance targeted by the engineer. Seismic friction dampers make achieving this performance objective easier, allowing for buildings that re-center even after large earthquakes. It is a common misconception that the building will re-center by the effect of the damping device alone. It is actually the elasticity of the structure’s elements that provide the re-centering forces to return the building to its original position. The main cause of permanent deformations in buildings are damage due to yielding or failure of structural elements. Using damping devices, such as friction dampers, engineers can dissipate the earthquake energy instead of allowing that energy to damage structural elements.

The amount of damage tolerated in a structure will depend on the performance criterion. For operational buildings, structural elements should be kept elastic in order to ensure minimal to no damage to the building. In cases where the performance objective is rather lifetime safety, some permanent deformation is tolerated and some of the earthquake energy will be absorbed by plastification of structural elements. The re-centering capability of a building is therefore dependent on a function of how much of an earthquake’s energy can be stored elastically within its structure and how quickly the energy can be dissipated.

The objective of any damping device is to dissipate energy as efficiently as possible and thereby protect the structure. Friction dampers are most efficiently used within elastic structures which provide the energy storage and some hysteretic damping while the damper provides only energy dissipation.

Self centering dampers Friction dampers can also be designed to provide re-centering capabilities (energy storage). The problem is that performing the task of re-centering within the damper sacrifices energy dissipation capacity (storing the energy instead). Therefore, designing with them is not as efficient since their hysteretic loops are much smaller than pure energy dissipation type dampers.

The other question the engineer must ask him/herself is: What is the building I’m trying to re-center? This is a consideration that is usually overlooked, especially during retrofits. If the building is going to have considerable plastic deformation after the design earthquake, what is the purpose of re-centering? The other structural elements might be too damaged to be worth re-centering. Is the engineer sure that it will withstand the re-centering forces? Will it collapse in the attempt of re-centering?

For these reasons, it is very important that, from the beginning of the design, the engineer decides on the performance criterion for the building and that this is clear to the client. This is equally important when performance criterion are set by default in code usually being between Life Safety (LS and Collapse prevention (CP), as the client may not have the same level of understanding as the design engineer of the code.

This understanding of performance objectives help the engineer better understand what task the dampers are trying to accomplish for the building. Usually, when this reflection is done, the engineer realizes that the most cost-effective way to re-center a building after an earthquake is by giving a portion of the earthquake force to the seismic friction dampers and the remaining to the rest of the structure.

The optimal slip force in the dampers produces the highest energy dissipation while transferring the least amount of energy (moments) to the frame. Parametric studies have shown that this force is produced when the dampers take less than 50% of the seismic shear in a given storey. Although you can assign the dampers as low or as high a force as you deem appropriate (especially when using large reduction factors), the closer you are to this optimum slip load the more efficient your design will be. In structural seismic retrofitting for instance, this usually prevents the need to strengthen structural elements and foundations. In the case of new structures, it allows engineers to design more efficient and economical structures.

For quick calculations, use a value of approximately one third of the seismic shear of a given story or less if using small reduction factors. This force divided by the cosine of the angle formed by the brace and the floor will be your Optimum Slip Load.

When computing the shear force in the building you must do it initially without dampers. Then proceed to locate them in the model and apply the parameters in the design section.Please don’t hesitate to contact Fuji Engineering design team to receive support on how to find the slip Load in your project and to how integrate the dampers.

Sometimes the seismic design force has been so significantly reduced by reduction factors (ductility) that it ends up being of smaller magnitude than the wind load in some combinations. When this occurs, the easiest solution is to increase the Slip Load slightly, so that it is at least 30% higher than the wind governing case. By doing this, you avoid over stiffening the building, thus bringing less acceleration and therefore forces in the seismic case.

With this small change, the structure has received a very efficient solution because it has received the exact increase in stiffness it needed, no more. This is because dampers work as common braces below the slip load. Therefore, the building will continue limiting seismic forces at a force only slightly higher than it was previously, bringing the building to an even higher level of performance against the MCE.

The friction damped brace or yielding restrained brace (YRB) is modeled as a link element in most software. In other words, it is modeled as a fictitious yielding brace.  Because the Ten-Co seismic brake (friction damper) can be treated as an ideal elastoplastic element, this allows the application of Wen’s model. While a simplification of the damper’s behavior, the Wen model simplifies the analysis.

A yielding brace or Buckling restrained brace (BRB) would yield and begin to deform allowing the building to absorb and dissipate the earthquake’s energy.  However, the brace would need to be replaced after the earthquake and the capacity of the fuse element changes as the steel strain hardens. In contrast, the Ten-Co seismic brake (inline seismic friction damper) is a damage free approach and slips instead of yielding, and, by means of the elasticity of the primary structural elements returns to its original position. This is an important distinction as the technology reduces displacements through energy dissipation allowing the primary elements to remain within their elastic range (e.g. 1%of storey height or less in some structures). Studies have shown that a moment frame capable of even just 25% of the slip load elastically is sufficient to recenter the damper. Other studies have shown that the moment resistance in shear tabs can also be sufficient in many cases. Please contact us for detailed references.

The inline (linear) friction damper’s slip load remains symmetric in tension and compression (hence the name Ten-Co), and has a high initial stiffness and is independent of displacement. This important characteristic simplifies modeling and maximizes energy dissipation as large displacements are not required in order to dissipate significant amounts of energy. For very large spans with low loads or tension only bracing please see our X-brace rotational friction damper.

The Ten-co Seismic brake’s hysteretic curve allows the damper to be modeled as a link in static, dynamic and non-linear analysis. The only information needed is the properties of the link which in this case is a fictitious yielding brace with its own linear and non-linear properties. This can be modeled in popular software such as ETABS or SAP2000 using the parameters below. The hysteretic loop is characteristically rectangular and based on rapidly converting seismic energy to thermal energy: which maximizes the energy dissipation.

Slip Load should be equal to 75% of the actual brace’s yield strength and 130% of the service loads (e.g.wind shear). The mass of the damper will vary depending on the slip load and travel required. This technology allows new ways to answer architectural and customer constraints. We encourage you to contact us with questions you may have.

The friction damped brace or yielding restrained brace (YRB) is modeled as a link element in most software. In other words, it is modeled as a fictitious yielding brace.  Because the Ten-Co seismic brake (friction damper) can be treated as an ideal elastoplastic element, this allows the application of Wen’s model. While a simplification of the damper’s behavior, the Wen model simplifies the analysis.

A yielding brace or Buckling restrained brace (BRB) would yield and begin to deform allowing the building to absorb and dissipate the earthquake’s energy.  However, the brace would need to be replaced after the earthquake and the capacity of the fuse element changes as the steel strain hardens. In contrast, the Ten-Co seismic brake (inline seismic friction damper) is a damage free approach and slips instead of yielding, and, by means of the elasticity of the primary structural elements returns to its original position. This is an important distinction as the technology reduces displacements through energy dissipation allowing the primary elements to remain within their elastic range (e.g. 1%of storey height or less in some structures). Studies have shown that a moment frame capable of even just 25% of the slip load elastically is sufficient to recenter the damper. Other studies have shown that the moment resistance in shear tabs can also be sufficient in many cases. Please contact us for detailed references.

The inline (linear) friction damper’s slip load remains symmetric in tension and compression (hence the name Ten-Co), and has a high initial stiffness and is independent of displacement. This important characteristic simplifies modeling and maximizes energy dissipation as large displacements are not required in order to dissipate significant amounts of energy. For very large spans with low loads or tension only bracing please see our X-brace rotational friction damper.

The Ten-co Seismic brake’s hysteretic curve allows the damper to be modeled as a link in static, dynamic and non-linear analysis. The only information needed is the properties of the link which in this case is a fictitious yielding brace with its own linear and non-linear properties. This can be modeled in popular software such as ETABS or SAP2000 using the parameters below. The hysteretic loop is characteristically rectangular and based on rapidly converting seismic energy to thermal energy: which maximizes the energy dissipation.

Slip Load should be equal to 75% of the actual brace’s yield strength and 130% of the service loads (e.g.wind shear). The mass of the damper will vary depending on the slip load and travel required. This technology allows new ways to answer architectural and customer constraints. We encourage you to contact us with questions you may have.

Some software allows for the direct input of the hysteretic loop. In the case  that the engineer would like to perform the analysis using these features, the quasi-rectangular hysteretic loop can be used

Since the damper stiffness is equal to the brace stiffness up until it slips, the effective and brace stiffness are equal.

The damper slips at approximately constant load and therefore the post-yield stiffness ratio can be estimated at near zero, 0.0001.

The optimum slip maximizes energy absorption for a given frame configuration and a given lateral force. It has been found that this force is below 50% of the story shear but different forces are often selected by the structural designer depending on his/her constraints and objectives.

Once found, small changes to the slip load(e.g. +/-20%) have minimal effect on the structure’s response.

For quick calculations use 1/3 of the story shear, ensuring that the ratio of lateral brace stiffness to total lateral story stiffness (frame + braces) is strictly greater than 0.5 and constant throughout the building height. Please communicate with Fuji Engineering representative for further advice on how to integrate friction dampers in your project.

Quaketek friction dampers can be installed in

• Steel Frames
• Reinforced Concrete frames
• Concrete or Steel Shear wall
• Timber frames

They can be used in any lateral force resisting system as a damping system or as a reusable safety “fuse” to protect structures from inelastic deformation or failure.

While there are many possible methods of installing the friction damper the single diagonal tension compression configuration is commonly used. The next most common installation method tends to be in chevron where the damper is installed in the diagonals or sometimes installed at the interface between the beam and the braces. Friction Dampers can be customized to fit almost any building and the link below has commonly used slip loads and strokes.

Quaketek brand sponsored the 6th International Conference on Earthquake Engineering and Seismology held at Gebze Technical University on 13-15 October 2021.

At the Fuji Engineering - Quaketek booth, 35-year guaranteed dampers (that allow the building to move elastically while absorbing earthquake energy) and their added value were conveyed to our visitors. Quaketek products, the global leader in friction dampers, do not require maintenance and operate silently in case of earthquakes.

We would like to thank our valuable visitors for the interest shown to our booth.

Detailed information about the conference can be found at This Link.

Fuji Engineering participated in the 18th World Conference on Seismic Isolation (18WCSI) event held in Antalya on 6-10 November 2023. At the event, friction damper applications in Türkiye and other countries were introduced.

Detailed information about the event can be found at the link below
https://18wcsi-7icees.org/

Fuji Engineering participated in the TurkeyBuild Fair held at Istanbul TÜYAP Fair and Congress Center on March 23-26, 2022, at its booth number A111, Hall-2.
Friction dampers (that absorb earthquake energy) and application examples in various structures were introduced at our stand.
Critical structures can be strengthened against earthquakes without business interruption with Quaketek products.
We would like to thank our valuable visitors for the interest shown in our innovative earthquake technologies and Quaketek products.