Viscous Fluid Damper(VFD)

Viscous Fluid Dampers (VFDs) are mechanical devices designed to reduce structural vibrations through energy dissipation. They operate on the principle of fluid resistance and are commonly used in buildings, bridges, and industrial facilities subject to dynamic loading such as earthquakes or wind.
The purpose of this manual is to provide technical, operational, and compliance information about the selection, use, and maintenance of VFDs. This document outlines the working principle, specifications, standards, and practical implementation guidance.
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Viscous Fluid Dampers convert kinetic energy into heat through the movement of a piston within a cylinder filled with a viscous fluid. The resistance force generated is proportional to the velocity of movement and can be modeled by:
F = C × Vα
Where:
- F = Damping force
- C = Damping coefficient (depends on orifice size and fluid viscosity)
- V = Relative velocity of piston
- α = Velocity exponent (typically 0.1 to 1.0)
The damping force is nonlinear and depends on the geometry and properties of internal components and working fluid. These devices provide supplemental damping without stiffness, making them ideal for reducing response without altering the structure's natural period.
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Key components:
- Cylinder Housing: Encloses the damping fluid
- Piston Assembly: Moves within the cylinder to generate pressure
- Orifices: Regulate fluid flow
- Sealing System: Ensures containment of the fluid and prevents leakage
- End Mounts: Typically clevis or spherical bearings

Design features:
- No moving external parts
- Suitable for long-term use without maintenance
- Fail-safe design-if fluid is lost, unit defaults to passive state
Applications:
- Seismic energy dissipation
- Wind damping
- Pedestrian vibration control
- Machinery isolation

Producing Process:

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Viscous Fluid Dampers are precision-engineered devices tailored to meet a wide range of structural damping requirements. Below are the general technical specifications typically found across standard damper models:
4.1 Force and Stroke Ranges
• Maximum Damping Force: 50 kN – 5,000 kN
• Stroke Capacity: 50 mm – 750 mm (custom designs available)
• Velocity Range: Up to 3 m/s
• Velocity Exponent (α): 0.1 to 1.0 (tuned per design)
4.2 Operating Conditions
• Operating Temperature: −40 °C to +70 °C
• Storage Temperature: −50 °C to +85 °C
• Suitable for humid, marine, or corrosive environments with optional coatings or stainless materials
4.3 Burst and Proof Pressures
• Proof Pressure: 1.5 × Operating Pressure
• Burst Pressure: > 2.5 × Operating Pressure
4.4 Materials and Fluids
• Housing: Carbon Steel or Stainless Steel
• Piston Rod: Chrome-plated Stainless Steel
• Seals: Welded Metal Bellows
• Fluid: Silicone-based or Synthetic Oil (VV-D-1078 compliant)
4.5 Typical Specification Table

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It can be seen from the damping force-velocity curve that when α = 0.1, as the velocity increases, the force increases slightly. When α = 2, the situation is opposite, and when α = 1, it is between the two cases.
From the damping force-displacement curve, it can be seen that when α = 0.1, the hysteresis loop is the largest. When α = 2, it is the opposite, and when α = 1, it is between the two situations.
Therefore, when the structure requires energy dissipation and shock absorption, the velocity index α is usually selected to be between 0.2 and 0.8. When the structure requires load distribution and transfer, the velocity index α is selected to be 2.

Dampers are characterized by non-linear force-velocity behavior with minimal phase lag. Performance graphs are typically supplied for each model. Typical metrics include:
• Force vs. Velocity (F-V) Curves
• Force vs. Displacement (F-D) Hysteresis
• Damping Force Consistency vs. Temperature
Designs ensure full energy dissipation with minimal rebound or lag. F-V curves are tuned by modifying orifice size and fluid properties.
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Viscous Fluid Dampers conform to international design and testing standards:
6.1 American Standards
• ASCE/SEI 7-22: Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Seismic provisions)
• AISC 341-22: Seismic Provisions for Structural Steel Buildings
• ASTM A370 / E2126: Mechanical testing methods for structural devices
• ICC-ES AC156 / AC494: Acceptance criteria for non-structural and structural damping devices
• OSHPD OSP: California seismic compliance
6.2 European Standards
• EN 15129:2018: Anti-seismic devices
• EN 1998-1 (Eurocode 8): Seismic design of buildings
• ETAG 001 / EAD: European Assessment Documents for construction products
• CE Marking: Products meeting EN standards must conform to CE performance declaration
6.3 Chinese Standards
• GB/T 24338.1–2009: Design specification for viscous dampers
• JGJ/T 209-2010: Code for seismic design of isolation and energy dissipation systems
• JT/T 926-2014: Specifications for highway bridge damping devices
• GB 50011-2022: Code for seismic design of buildings
All devices must be tested per GB and EN protocols, including low-cycle fatigue and temperature stability.
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Dampers may be installed in various bracing or isolation arrangements:
• Chevron Bracing: Mounted in inverted V brace configurations
• Diagonal Bracing: Positioned within a single structural bay
• Base Isolation Dampers: Installed between structure and foundation
• Outrigger and Linkages: Connecting core wall systems

Each configuration requires pinned clevis mounts and axial alignment to ensure unrestricted motion. Spherical bearings accommodate rotational tolerances.

Installation tips:
• Avoid misalignment or bending of piston rod
• Verify pin-tightness and bearing lubrication
• Pressure test post-installation if specified

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• Every unit tested for performance up to 100% rated stroke and velocity
• Cyclic durability: Over 100 million cycles
• Factory tests include:
o Hydrostatic burst test
o Full-scale dynamic testing (velocity ramping)
o Leak detection
o Force calibration with ±5% tolerance
Manufacturing typically follows ISO 9001 or AS9100 protocols. FAT and SAT documentation available.

Type testing report & testing reports issued by the Third party

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• Maintenance: Maintenance-free under standard service; no lubrication required
• Fire Resistance: Silicone fluid rated for high temperatures; metal seals are fireproof
• Safety Factors: Typically designed with 2.0× safety margin for dynamic pressure
Inspection is recommended after seismic events or at 10-year intervals.
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Applications include:
• Seismic retrofit of heritage and critical infrastructure
• Vibration control in towers, footbridges, and stadiums
• Wind damping in supertall buildings
Case Study:

A major footbridge exhibiting pedestrian-induced vibrations was retrofitted with 40 kN dampers. Post-installation measurements showed a reduction in peak acceleration by 95% and elimination of resonant oscillations.
Another example includes base-isolated hospitals using dampers to minimize structural response during earthquakes, enabling full operability post-event.
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