Structural Analysis of Single Diagonal Damped Brace
The damped brace is modeled as a link element in most software. In other words, it is modeled as a fictitious yielding brace. Because the 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 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.
In contrast, the friction damper slips instead of yielding and by means of the elasticity of the primary structural elements, returns to its original position.
The damper’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 following parameters.
*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 at anytime with any 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
Finding the Optimal Slip Load
The optimum slip maximizes energy absorption for a given frame configuration and a given lateral force. It has been found that this force is usually below 50% of the story shear but it can always vary depending on the restrictions the structural designer has in his/her project or depending on his/her objectives for the structure’s response performance.
Once found, small changes to the slip load(e.g. +/-20%) have minimal effect on the structure’s response.
Research has shown that optimum Slip Load is found at below 50% of the story shear. Please communicate with our Engineering Department for further advice on how to find it in your project. For quick calculations use between 35 – 50%, ensuring that the ratio of lateral brace stiffness to lateral braced frame stiffness is strictly greater than 0.5 (generally between 0.7 and 0.9) and constant throughout the building height.
Connections and Installation
Can be installed in
- Steel Frames
- Reinforced Concrete frames
- Concrete or Steel Shear wall
- Timber frames
While there are many possible methods of installing the friction damper the single diagonal tension compression configuration is commonly usedFriction Dampers can be customized to fit almost any building and the link below has commonly used slip loads and strokes.
Friction Damper Catalog
The Catalog will provide you with some examples of standard dampers, their dimensions, and masses.
When you complete your analysis provide us with the required slip load and stroke and Quaketek will custom design the damper you require.