Dynamic performance of the Mill on the Exe footbridge

The Mill-on-Exe footbridge (Figure 1) was opened in 2003. The span is supported by two pairs of stay cables, whose tensions are balanced by a massive counterweight, and is equipped with six tuned mass dampers (TMDs), which are designed to suppress pedestrian-induced vibrations.

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Figure 1: Prof. Reynolds explains the operation of tuned mass dampers to MSc students Elmar Talibli and Ed Court

A team from the Vibration Engineering Section (Figure 2) supported two  University of Exeter undergraduate engineering student projects – one about performance of the tuned mass dampers and one about flow of energy from the pedestrian generating dynamic response to damping sinks, including TMDs.

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Figure 2: James Bassitt, Vincent Ao, Yan Xu and Ahmed Mohammed taking a break.

Measurements used a set of 21 Honeywell servo-accelerometers (Figure 3) and a set of 11 APDM Opal inertial measurement units (IMUs). Opals are intended for sports biomechanics applications, but they are well suited for research into human-induced structural vibrations e.g. of footbridges, and this is the first time they have been used to study the flow of energy.

 

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Figure 3: Thomas Lynchehan function tests a servo accelerometer

Energy was supplied by undergraduate students, either jumping or running (Figure 4).

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Figure 4: Josephine Benthall crossing the bridge

The testing provided a set of experimental modal properties, which validated the modeling by the consultant (Flint & Neill) and confirmed the effectiveness of the TMDs.

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VES starts STORMLAMP research project into lighthouses

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With 95 per cent of the UK’s international trade transported by sea, rock-mounted lighthouses have a crucial role to play in safe navigation – but the longevity of these historical structures is threatened by extreme weather.

So, the Vibration Engineering Section (VES) have teamed up with researchers at Plymouth University and University College London to start a project assessing six of the most vulnerable lighthouses in the UK and Ireland.

VES Experimental Officer James Bassitt joined Julian Seipp, Senior Technician at Plymouth University on Longships Lighthouse at St Just near Lands End, to begin STructural behaviour Of Rock Mounted Lighthouses At the Mercy of imPulsive waves (STORMLAMP). An EPSRC funded project, STORMLAMP will combine field, laboratory and mathematical/computer modelling methods.

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James and Julian were given access to the lighthouse by General Lighthouse Authority, Trinity House and were flown there by helicopter, along with a maintenance crew. There, they retrieved data gathering geophones previously installed on the lighthouse by the University of Plymouth as part of a pilot project leading into STORMLAMP, and replaced them with triaxial accelerometer data logging equipment. In addition, they carried out a full survey of the lighthouse to help them to come up with a long term monitoring solution and testing plan.

James Bassitt said: “I would like to thank Trinity House, including Ian Gorvin and Malcolm Johns for their support on the day and for their help with future planning. We have taken the geophones back to Exeter to benchmark them against highly sensitive accelerometer data logging equipment.

He added: “The next stage will be to carry out a data gathering exercise at a lighthouse off the coast of Guernsey in June.”

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As part of STORMLAMP, field instrumentation and procedures will be developed by the University of Exeter (James Brownjohn and James Bassitt) for the highly challenging constraints. Meanwhile, UCL (Dina D’Ayala will create test data guiding of multi-scale numerical simulations for lighthouses that can be used with the full-scale data to diagnose observed performance in the long term monitoring.

These models will link with advanced physical and CFD simulations by Plymouth University’s COAST Laboratory (Alison Raby-who leads the project- and Deborah Greaves).

STORMLAMP will move to a focus of one lighthouse for the following two winters. Based on these modelling exercises, the long term monitoring of a single structure will used to characterise the wave loading in-situ at full scale. The project will support performance management of such structures worldwide.

STORMLAMP – STructural behaviour Of Rock Mounted Lighthouses At the Mercy of imPulsive waves

The Vibration Engineering Section is pleased to announce that the Engineering and Physical Sciences Research Council (EPSRC) will fund a research project STORMLAMP – STructural behaviour Of Rock Mounted Lighthouses At the Mercy of imPulsive waves.

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VES Experimental Officer James Bassitt joining Julian Seipp, Senior Technician at Plymouth University on a helicopter flight to Longships Lighthouse, near Lands End


Rock-mounted lighthouses play a vital role in safe navigation but, like other critical infrastructure, their longevity is threatened by extreme weather. Virtual navigational aids such as GPS are fallible and mariners will continue to need physical visual aids. The loss of any reef lighthouse will be incalculable in terms of safety, trade and heritage.

STORMLAMP combines field, laboratory and mathematical/computer modelling methods to assess six of the most vulnerable rock lighthouses in the UK and Ireland and will move to a focus of one lighthouse for the following two winters.

Field instrumentation and procedures will be developed by the University of Exeter (James Brownjohn and James Bassitt) for the highly challenging constraints. Meanwhile, UCL (Dina D’Ayala will create test data guiding of multi-scale numerical simulations for lighthouses that can be used with the full-scale data to diagnose observed performance in the long term monitoring.

These models will link with advanced physical and CFD simulations by Plymouth University’s COAST Laboratory (Alison Raby-who leads the project- and Deborah Greaves).

Based on these modeling exercises, the long term monitoring of a single structure will used to characterise the wave loading in-situ at full scale. The project will support performance management of such structures worldwide.

Total EPSRC funding is £1.03m, with £173k to Exeter, and the project runs from 1st April 2016 to 30th September 2019.