The Great London Plane of Ely is believed to have been planted in 1674. At more than 40 metres tall, it is recognised by The Tree Council as the largest London plane in the UK and one of its Top 50 Great British Trees. Although the tree is in good health, a whole-tree survey showed that additional support is required to help it continue to prosper.
Engineers at the University of Cambridge are working with arborists to develop a cable-bracing system for the tree. The aim is to support key areas while allowing the tree to retain natural movement. To guide the design, the team built a structural finite-element model from LiDAR geometry and measured the tree’s wind-driven response with accelerometers.
The exceptional scale and complex branching structure of the tree make dynamic measurement difficult. Accelerometers provide accurate data at their installed locations, but only a limited number could be fitted. The team therefore needed an additional way to interpret the point measurements and observe how larger parts of the tree moved together.
WaveCam was used to perform operational modal analysis from video. Recordings were captured from several ground-level viewpoints with a tripod-mounted iPhone SE. Each analysis used 50 seconds of video recorded at 24 frames per second, corresponding to 1,200 frames and a frequency resolution of 0.02 Hz.
The setup was completed within a few hours. Because the analysis was based on video, it provided a full-field view of visible sections of the tree without adding further sensors or cabling to the branches. In this project, WaveCam complemented the accelerometers; it did not replace the wider structural assessment.
The recordings showed clear local and global vibration modes. On the southern limb, the WaveCam results visualised bending responses at approximately 0.38 Hz and 0.44 Hz. A whole-tree operational deflection shape was also identified at approximately 0.44 Hz.
These mode shapes helped associate spectral peaks in the accelerometer data with specific movement patterns. They provide additional evidence for identifying dynamic bending behaviour in parts of the tree affected by damage and decay, informing the engineering assessment behind the planned bracing system.
Source:
| Measurement object | Great London Plane of Ely, East Cambridgeshire, UK |
| Excitation | Natural wind loading |
Camera | iPhone SE on a tripod |
Frame rate | 24 fps |
| Recording length | 50 s / 1,200 frames |
| Frequency resolution | 0.02 Hz |
| Analysis | Video-based operational modal analysis with WaveCam |
| Complementary data | LiDAR geometry, tri-axial accelerometers and a finite-element model |
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