The growing trend for open plan offices means modern office buildings are typically constructed with thinner concrete flooring slabs and longer unsupported spans than more traditional buildings. A side-effect of this type of construction is the tendency for longer spans to ‘bounce’ under the weight of people walking across the floor — a nuisance to staff as they concentrate on work.
Civil engineers Professors Emad Gad, John Wilson and colleagues from the Swinburne’s Centre for Sustainable Infrastructure have recently developed a floor vibration damping technology that is sufficiently compact and cost efficient to fit into existing offices. The technology has already been retrofitted in buildings in Australia and the UK.
Floor vibrations might seem a trivial problem, but movements of as little as a tenth of a millimetre can cause significant discomfort to workers seated at desks. Maximum permissible foot traffic vibration limits are now set in design guidelines around the world.
While vibrations can be reduced by increasing the stiffness of the floor with structural beams, and by ‘damping’ the vibrations with added weight, these approaches can often only be implemented during construction because they are too bulky to retrofit in a working office environment.
“Modern open-plan, ‘electronic’ offices tend to be long span, lightweight and with little furniture,” says Gad. “Floors that suffer excessive vibration due to people walking can be rendered unusable, even though they are perfectly safe. Until now, there was no proven technology that could be economically and efficiently applied to fix such problems.”
Gad and Wilson’s team has developed an unprecedented solution, a tuned mass damper (TMD), which is cost-effective, proven and quick to install.
The TMD consists of multiple flat beams of viscoelastic rubber sandwiched between steel plates, each fixed at one end and weighed down with a steel plate at the other. The beauty of the design is that it requires no electrical power and is simple and cheap to construct. It is less than 15 centimetres high, so easy to install in the standard sub-floor gap found in most offices.
By matching the resonant frequency of the TMD to that of the measured floor vibration, the TMD system has been demonstrated to reduce the peak acceleration of vibration by more than 50 per cent, bringing the vibration down to levels below the threshold of discomfort — an elegantly simple solution to a growing global problem.
As this new TMD technology is now commercially available, Gad says the group will continue designing and building bespoke dampers to meet clients’ needs. “We design and manufacture the dampers ourselves and either install them or provide instructions,” says Gad.