Tuned Mass Dampers
A model depicting a large unsupported span supoorted by cellform beams. Low resonances (sub 8.5Hz)
and no means for additional stiffening or support make this a good application for TMDs
Tuned Mass Dampers (TMD) or Tuned Mass Absorbers (TMA) are a highly effective method for preventing the effects of resonance. These are systems which work against structural resonances damping out their effects by means of a mass, spring, damper arrangement that resonant out of phase with the structure removing the resonant energy and therefore the “bounce”!
All structures have resonant frequencies and all structures will vibrate. The challenge lies in managing the resonances and vibration frequencies such that they do not impact the usability of the structure or the experience of those who use it.
Certain buildings and designs can be more problematic than others when accommodating their vibration and dynamic characteristics. Long spans, such as bridges and large halls will typically have very low natural frequencies that are prone to being triggered by foot traffic and human activity - Consider bouncing on a pedestrian suspension bridge across a river to visualise how much motion can be excited in the structure from relatively little input. For such structures it typically is not possible to stiffen or adjust to prevent this motion and so TMDs prove an ideal and cost effective solution.
As with long spans, tall and slender structures suffer from side to side sway that can be triggered from wind loading and again TMDs provide a solution. TMDs are often seen on chimney stacks and sky scrapers. Higher frequency problems can also be solved using TMDs, Xi have developed TMDs for gearboxes aimed at tackling the rotational and torsional motion of the gearbox.
Xi Engineering can provide assistance and design bespoke tuned mass damping solutions, if you have an application that a tuned mass damper may help or be required, give Xi a call and our engineers will look forward to discuss your requirements.
Xi have experience in designing complex and novel TMDs. Xi’s SQT (Seismically Quiet Tower) is a tuned mass damper designed to target resonant frequencies of wind turbines that are transmitted in to the ground. These can be problematic where a wind farm is located near seismically sensitive equipment, such as geological and optical observatories. Xi’s SQT also has the benefit of reducing structural loading and fatigue which is an increasing concern as tower heights increase.