Seismic DamperTM

DC White Consulting Engineers have been involved in seismic design of safety-critical structures for more than 25 years. To this end we have designed, developed and are in the process of producing a range of structural dampers, the Altoona Damper, which uses simple proven techniques to provide isolation and greatly increase damping of a structure - but only at the time of a seismic event. The Altoona Damper is quite different from most seismic 'dampers'; it is not a soft rubber or spring (which does not actually damp, buts serves as an isolator); it is a structural member which truly dissipates energy when required. It can be incorporated into any critical steel framed structure such as buildings, support frames and cranes. For normal duty it is completely passive; for seismic or fault loading it is an isolator and damper. The concept is simple: a damper is placed directly into the seismic input load path but it is locked to carry all design loads as a “rigid” unit. When the design load is exceeded (tensile or compressive, plus an agreed margin), the foolproof lock is instantly released and the damper/isolator becomes effective, greatly reducing the forces input to the critical structure.In the case of a gantry crane, the Altoona Dampers could be fitted between the bogies and the cross-travel beam. An appropriate arrangement can be fitted in the longtravel direction (if required). Struck by an earthquake, the unlocked Altoona Dampers would then operate as low-stiffness but highly damped units.Careful consideration is given to the damper design as an integral part of the system toensure that…• it does not compromise normal operation,• the structure is totally stable for both locked and unlocked dampers,• the impulse loading associated with the unlocking is minimised,• the damping level is appropriate, avoiding unintended enhancements,• the damper can be readily re-locked after the event, allowing the structure tobe quickly put back into serviceThus, for effective operation, it is essential that there is full integration between the DC White and structural design teams so that the damper is correctly sized and installed. As previously stated, the Altoona damper is seen as being ideally suited to being incorporated into any critical steel- framed structure such as buildings, support frames and cranes. For normal duty it is completely passive; for seismic or fault loading it is an isolator.

For more information on Seismic DamperTM talk to DC White Engineering Consultants