The Role of Friction in Seismic Design
- Friction has long been used in earthquake-resistant design to convert kinetic energy (harmful to structures) into thermal energy (harmless).
- However, traditional friction-based devices have some drawbacks:
- Limited load-carrying capacity compared to other systems.
- Risk of jamming due to friction, preventing the device from returning to its original position after displacement.
- If the device cannot return to its initial position, it may require manual resetting, which is costly and, in some cases, may even necessitate the demolition of the structure.
2. Innovative Solution by Pierre Quenneville and Pouyan Zarnani
Two structural engineers, Pierre Quenneville and Pouyan Zarnani, developed a new type of seismic connector that addresses the weaknesses of traditional friction-based dampers. Their invention:
- Eliminates the drawbacks of friction-based systems,
- Stores the energy from the earthquake that disrupts the structure’s balance,
- Uses this stored energy to return the structure to its original equilibrium position after the earthquake.
3. How It Works
- The device combines friction-based energy dissipation with a mechanism that stores and releases energy.
- During an earthquake:
- The sliding friction mechanism dissipates energy as heat.
- Simultaneously, the device stores a portion of the energy in a flexible element (e.g., springs or elastomers).
- After the earthquake:
- The stored energy is released, helping the structure return to its original position.
4. Advantages of the New System
- Self-Centering: The structure can return to its original position without manual intervention.
- Improved Performance: Combines the energy dissipation of friction with the resilience of flexible elements.
- Cost-Effective: Reduces the need for costly repairs or demolition.
- Enhanced Safety: Minimizes residual displacements, ensuring the structure remains functional after an earthquake.
5. Simulation Focus
In this simulation, we will:
- Analyze the behavior of friction-based sliding flexible connectors under seismic loads,
- Evaluate their energy dissipation and self-centering capabilities,
- Compare their performance with traditional friction-based systems.
The friction-based sliding flexible connectors developed by Pierre Quenneville and Pouyan Zarnani operate through a clever combination of friction, energy storage, and self-centering mechanisms. Here’s a detailed explanation of how they work:
1. Activation of the Sliding Mechanism
- When the force acting on the middle plate exceeds the friction force between the plates, the middle plate begins to slide horizontally.
- The middle plate has a saw-tooth structure, which causes it to push the upper and lower plates in a direction perpendicular to its movement.
2. Compression of Disk Springs
- The upper and lower head plates are equipped with disk-shaped springs.
- As the middle plate slides and pushes the upper and lower plates, these springs are compressed.
- The earthquake energy is converted into potential energy and stored in the compressed springs for later use.
3. Energy Dissipation
- Excess kinetic energy from the earthquake is dissipated as heat through friction between the plates.
- This ensures that the harmful energy is safely removed from the system.
4. Self-Centering Mechanism
- After the earthquake, the potential energy stored in the compressed springs is released.
- This energy helps the system return to its original position, ensuring the structure is realigned without manual intervention.
In this example simulation, the self-centering capability of the friction-based sliding flexible connector is examined. The middle plate is pulled twice by 20 mm and then released, allowing us to observe the system’s ability to return to its original position.
1. Simulation Setup
- Middle Plate Movement:
- The middle plate is displaced horizontally by 20 mm twice.
- This simulates the sliding motion during an earthquake.
- Release:
- After the displacements, the middle plate is released, and the system’s response is observed.
2. Self-Centering Mechanism
- As the middle plate slides, it compresses the disk-shaped springs in the upper and lower head plates.
- The potential energy stored in the springs is used to return the system to its original position after the displacements.
3. Hysteretic Behavior
- The flag-shaped hysteretic curve observed in the simulation is a clear indicator of the system’s self-centering capability.
- Flag Shape: The curve shows that the system returns to its original position after each cycle of displacement, with minimal residual deformation.
- Energy Dissipation: The area within the curve represents the energy dissipated as heat through friction.
4. Key Observations
- Self-Centering: The system successfully returns to its original position after each displacement, demonstrating its self-centering ability.
- Energy Efficiency: The flag-shaped curve confirms that the system effectively stores and releases energy while dissipating excess energy as heat.
- Resilience: The system can withstand multiple cycles of displacement without losing its functionality.
Simulation Results:
- Displacement Cycles: Two cycles of 20 mm displacement.
- Hysteretic Curve: Flag-shaped curve indicating self-centering behavior.
- Energy Dissipation: Efficient dissipation of excess energy through friction.
- Residual Deformation: Minimal to no residual deformation after each cycle.
