A direct acting damper system is when fluid viscous dampers are integrated into a building or bridge’s structure to help absorb energy due to wind, seismic events, or pedestrian activity. The dampers are literally dispersed or “distributed” throughout the structure to capture the movement energy of the structural frame. This type of system is found most common in low to mid-rise buildings, and long span bridges.
While many methods exist to implement direct acting (distributed damping) in a structure, the underlying concept is to connect the dampers where motion will occur, such as between beam and column joints or between floor levels which deform relative to one another in a shearing-type motion. Continue reading to learn more about some of the most common configurations used in direct acting damping systems.
Taylor Devices offers a unique solution for those seeking more open bays. This new application of proven fluid damper technology provides all the benefits of traditional seismic and wind configurations but with minimal blockage of buildings bays. The energy of the moving bay or structural frame is translated through the open space damping system, then converted to heat and dissipated into the air.
Toggle frames can be used as a mechanism to amplify deflections into the damper in otherwise stiff, or tiny deflection situations, creating a more efficient damping system. Toggle frames utilize a bent-brace mechanism theory to capture deflections in one plane and translate the deflections into another plane and therefore provide very efficient damping, and energy removal.
In this configuration, the dampers are placed horizontally, and connected to a frame (chevron) that is intended to be near-rigid with the floor it is connected to. The advantage with this direct damping orientation is that the horizontal flexibility of the structure injects this full movement directly into the horizontal orientation of the damper. However, a small amount of motion can be lost due to the constraints of the attainable stiffness of an economical chevron frame.
A variation of the standard diagonal damping configuration, using two diagonal dampers that typically meet at the center of the beam. Additional beam stiffening is required to carry the vertical load components in this configuration.
A very common method of applying distributed damping to a structure is to connect the dampers to diagonal corners or center of a structural frame or bay. In this orientation, the horizontal movement of the structure allows an angular component of the full deflection to go into the damper. This takes the motion directly to the next floor level through a strong tension/compression member.
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When it comes to bridges that are subjected to seismic, wind, or traffic inputs, engineers must decide how to reduce or eliminate lateral motion and feedback. One potential solution is changing the frequency, or period, by stiffening the bridge through additional bracing or piers. However, when going this route, a substantial amount of structural modifications may be required leading to an increase in weight of the bridge and substantial costs. Additionally, this can also affect the unique architecture of the bridge.
Another solution is to add a direct acting damping system to the bridge to reduce resonant deflections to a low level. This system can increase damping levels from the usual 0.5%-1% critical damping to a 20% critical damping range. Our fluid viscous dampers have the unique ability to simultaneously reduce both stress and deflection within a structure subjected to a transient vibration. This is because a fluid viscous damper varies its force only with velocity, which provides a response that is inherently out-of-phase with stresses due to flexing of the structure. To learn more about direct acting damping systems for bridges, please contact our team today.