Gdansk, Poland – Scientists at the Gdansk University of Technology have investigated the effectiveness of polyurethane flexible adhesive in reducing structural vibrations in response to dynamic loads.
This is important when designing buildings that may be affected by wind, earthquake or crowd load effects, where dampening properties make them more resistant to the stresses.
When using composite materials to strengthen structures such as masonry or infilled reinforced concrete frames, stiff adhesives made from mineral mortars or epoxy resins are commonplace. However, these stiff, brittle adhesives do not add ductile or damping properties. Might polyurethane flexible materials be more successful?
In the study, two aluminium cantilever beams were used to simulate structural elements, both with and without a layer of polyurethane tape. These were first analysed to check the damping of the unconstrained polymer layer.
Then, they took a composite beam comprising two flat aluminium beams, bonded using a PU adhesive, and checked the damping of the constrained polymer layer. They also compared dynamic parameters, including modes of free vibrations, corresponding natural frequencies and damping ratios.
Finally, they addressed the problem of the additional mass of the applied polymer layer which, they said, influences the frequencies and damping of the tested structure. They proposed a separating procedure that enables the corrected real values for the damping of the adhesive layer.
The study showed found that the PU adhesive layers led to a significant reduction in the vibration of tested beams, whether or not the conditions were constrained. Importantly, the stiffness of the beams was almost entirely preserved.
The study has been published in the journal Polymers.