Energy Harvesting from Slender FRP Pedestrian Bridges

Energy Harvesting from Slender FRP Pedestrian Bridges

Linssen, Rob (TU Delft Civil Engineering and Geosciences; TU Delft Applied Mechanics)

van der Meer, F.P. (graduation committee)
Pavlovic, M. (mentor)
Sluys, Lambertus J. (mentor)
Schutte, William (mentor)

Delft University of Technology

Civil Engineering | Structural Engineering

2020-04-24

The Rotterdam municipality is constantly busy replacing old footbridges that have reached their lifetime. Lately, this is done using modern materials, such as fibre-reinforced polymers (FRP). FRP is a relatively light-weight material that has a high yield strength, which allows for aesthetically pleasing, very slender designs. Governing for such designs is often the dynamic behaviour of the bridge: its eigenfrequency may very well lie within the `critical range' of common footfall frequencies. If the step frequency of a pedestrian crossing the bridge lies near the eigenfrequency, a high dynamic amplification factor occurs: high vertical acceleration values for the bridge deck will occur, which means discomfort for the pedestrians.

In this thesis, a sustainable solution to that problem was sought. Rather than using pile foundations to clamp the bridgeheads (and thereby increase the eigenfrequency out of the critical range), it was investigated whether the kinetic energy can be harvested from the bridge. Ideally, this both dampens the vibrations and provides free, sustainable energy.

Several theoretical models were developed to describe the behaviour of an existing footbridge for which data is available. Adaptations to these models were made in the form of either extra dashpots or a tuned mass damper (TMD). In both cases, the dampers are regenerative, i.e. able to harvest energy.

It was shown that adding a TMD provides the best energy harvesting performance. From a practical perspective, it has some advantages as well, such as universal applicability. The parameters in the single degree of freedom (SDOF) model were optimized for maximum energy harvesting while still keeping the vertical deck acceleration at reasonable levels. Finite element analysis largely confirmed these design choices, and showed that reducing the vibration levels is certainly possible with only a relatively small TMD. For a single person crossing at near-resonant footfall frequency only leads to a vertical acceleration of about 1.5 m/s.

The amount of energy that can be harvested in such a way is small but non-negligible: about 26 Joules worth of energy is estimated to be gained by an `average' person crossing the bridge. This is taking into account system efficiency as well.

A literature study concerning real-world energy harvesting systems was performed, and showed the possibility to closely emulate the theoretical behaviour that was assumed for the regenerative dashpots. This can be done using electromagnetic dampers in combination with proper power electronics design.

pedestrian bridge
vibration
Energy Harvesting
Tuned mass damper (TMD)
damping
deck acceleration
FRP

http://resolver.tudelft.nl/uuid:c7253bea-aea1-4536-8bd9-80d32aab5cdb

Student theses

master thesis

© 2020 Rob Linssen