The Velocity Lock-Up Device (LUD), also known as a Shock Transmission Unit (STU), is a velocity-sensitive passive protection device for highway and bridge structures. It moves freely during slow displacements (thermal expansion, creep, etc.) and locks instantly under high-speed events (earthquake, strong wind, braking shock), temporarily rigidly connecting the girder and piers for integrated force distribution and enhanced structural safety.
Working Principle
Adopts velocity-sensing hydraulic/mechanical locking technology triggered by a preset velocity threshold
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Low speed: Medium flows freely / mechanism unlocked, allowing normal deformation without restraint
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High speed: Flow passage closes rapidly / mechanical engagement activates, device locks instantly as a rigid force-transfer component
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Fast response, reliable locking, non-energy-dissipating, only transmits force and coordinates structural behavior
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Core Functions
- Low-speed free movement, high-speed locking for both long-term deformation and extreme loads
- Instant rigid connection under earthquake, wind, or braking loads to distribute impact and reduce damage
- Reduces stress on bearings, piers, and girders to extend bridge service life
- Passive operation without power or control, stable and maintenance-free
- Compatible with dampers and bearings for improved seismic performance
Product Features
Precise adjustable velocity threshold for various bridge designs
Wide range of rated load capacities for different bridge types
Fully sealed, anti-aging, corrosion-resistant, suitable for harsh environments
Easy installation for new bridges and retrofitting projects
Long service life, high reliability, minimal maintenance
Typical Applications
Highway bridges, urban viaducts, interchanges
Long-span bridges, continuous girder bridges, steel bridges
High-pier, large-displacement, seismic-priority bridges
Bridges in strong wind and high seismic zones
Seismic retrofitting and performance upgrading projects
Technical Highlights
- Velocity-sensitive triggering, different from ordinary dampers or restrainers
- Ultra-fast locking within milliseconds
- No interference with normal service, activates protection only in extreme conditions
- Compact structure, clear force transfer, excellent economic efficiency
- Complies with international and domestic bridge seismic and wind design codes