Introduction
The design and usage of pedestrian structures has changed substantially in recent years, leading to an increase in problematic post-construction vibrations due to in-service loading. The addition of extra concrete mass, supplemental beams to provide additional stiffness and mid-span props are some of the typical remediation measures for these structures. However, these solutions are far from ideal because of their
intrusive nature during the corrective phase and general costliness.
One alternative technology that could be used to help mitigate this problem, particularly in floor structures, is active vibration control (AVC). While this technology is relatively mature for the full-structure control of seismic- and wind-induced vibrations, its application to floor structures is in still its infancy, though field trials and a small number of implementations have shown considerable potential.
The relative complexity of active control has thus far precluded it from the structural engineers' domain, whereas the comparatively simple tuned mass dampers and constrained layer damping techniques are increasingly being considered, both for remediation and at the design stage.
In its simplest form, active control comprises a sensor (typically an accelerometer), a controller and an actuator. When the floor is excited, for example by human walking, the sensor detects the resulting structural motion and the signal is passed on to the actuator following modification by a controller. In this way a corrective force is applied to the structure that reduces the level of response.
This feedback approach has the very significant benefit of being effective over a broad frequency range, in stark contrast with tuned mass dampers (TMD) which inherently target only one mode of vibration and so require as many devices as there are modes to be controlled. Furthermore, while detuning is a potential problem of TMD installations, AVC controllers can be made adaptive in nature such that they respond to changes in structural dynamic properties, for example from rearrangement of furnishings or partition walls.