Lock-Up Devices- Also known as Shock Transmission Units

TechStar Lock-Up Device (LUD) sometimes referred to as Shock Transmission Units (STU), creates a rigid link at an otherwise moveable connection. During any sudden load, seismic, braking, train acceleration, ship collision or any other force acting on the bridge that would cause the bridge to move suddenly, the LUD becomes a rigid link and the forces are then transmitted through the structure. The concept is to share the load throughout all piers and abutments. By temporarily creating a rigid link where expansion and contraction normally occur, the bridge can be modeled as completely fixed. In continuous bridges the fixed pier no longer must resist the longitudinal forces as all other piers equipped with LUDs would be fixed during this loading condition. In accordance with AASHTO, all testing is done by independent laboratories to assure the performance of the device.

Design Criteria
In order to design an LUD, it is necessary to know the following:

  • Rate of expansion and contraction during normal operation
  • Total stroke (mm, in.) of the transmission rod through full range of normal movement
  • Ultimate design force to be transmitted through the LUD
  • Geometry of the surrounding application
  • Design code that is applicable

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