Check out the National Instruments case study on a Jiangyin Bridge modal test at http://sine.ni.com/cs/app/doc/p/id/cs-17465
On Thursday 1st June, a team of researchers from the University of Exeter travelled to Watchet to perform testing on the Mineral Line Bridge. The bridge forms part of the West Somerset Railway, a heritage railway line with 20 miles of track in South West England. The team included Farhad Huseynov, Yan Xu, Jalil Kwad, Karen Faulkner and Linus Tonui.
The Mineral Line Bridge is located on the outskirts of Watchet and was originally constructed to carry the Minehead route over the West Somerset Mineral Railway. The Mineral Railway now operates as a footpath and cycle path open to the public. The bridge opened in 1962, has a single span of 14 m and is constructed skewed to the pathway beneath.
The aim of the testing was to measure the structural deformations of the bridge under loading from passing trains, a combination of steam and diesel engines. A series of strain sensors, inclinometers and LVDT sensors were installed on the bridge. A number of targets were also installed on the bridge to measure deflections using an Imetrum camera.
The strain sensors were installed below deck at mid-span, with the inclinometers installed above deck at each support, and quarter-span. Data was recorded during each passing train.
The Imetrum camera was used to measure deflections of the bridge under loading from the passing trains. Three Imetrum cameras were set up on tripods and targets were installed, one at mid-span on the bridge deck and two on the western abutment, previously identified as an area of interest.
The weather conditions were favourable, sunny with low winds. This led to limited interference from the environmental conditions, allowing for a clearer understanding of the train loading on the bridge.
Dubh Artach Lighthouse, Southwest of Mull on the Scottish West Coast was designed by Thomas Stevenson (father to the author Robert Louis), first ‘exhibited’ in 1872 and fully automated in 1971.
As part of the EPSRC STORMLAMP project, a team visited the lighthouse on 8th and 9th May 2017 to carry out a modal test. Alessandro Antonini took the modal test equipment by van from Plymouth University while James Bassitt and Karen Faulkner from the University of Exeter’s Vibration Engineering Section travelled via Glasgow Airport.
Dubh Artach helipad is just above sea level, so, as well as usual weather restrictions, helicopters (flying from the Trinity House depot in Oban) can only visit at low tide. Luckily, the weather was excellent, with zero cloud cover, perfect visibility and minimal wind.
Access to the lighthouse is via vertical steps and all equipment, including a 50 kg shaker, had to be hoisted to lantern level using a temporary crane.
The signal to noise ratio for forced vibration testing was perfect, providing extremely clear resolution of vibration modes, with the shaker mounted on the lantern level walkway, just visible in the photograph.
Conditions were also perfect for flying the survey drone, providing some stunning views:
After staying overnight on the lighthouse, the team returned to Oban, then to Exeter and Plymouth.
As part of the EPSRC-funded BAYOMALAW project, a team of researchers from Exeter and Liverpool travelled to Jiangyin in Jiangsu province, China to carry out a modal test of the Jiangyin Suspension Bridge.
Jiangyin Bridge has a single suspended span of 1,385m, with straight back stays. The concrete towers rise 191m above ground level and each have three hollow portal beams. The mid portal is illustrated by the bridge name in stylised Chinese characters, created by (and signed by) the former Chinese premier Jiang Zemin, who opened the bridge in 1999. At the time, the bridge was the world’s fourth longest span and the furthest downstream on the Yangtze River.
The 32.5m wide 3m deep steel box deck carries three traffic lanes (plus a narrow emergency lane) in each direction. There are 2.2m wide cantilevered walkways either side, although these are for maintenance as there is no pedestrian access to the bridge. These walkways were used by the test team for moving the loggers around.
The exercise was primarily an extreme test of the capabilities of two new technologies.
First, a new synchronised wireless logging system was created by James Bassitt (hardware) Vincent Ao and Emma Hudson (software). Four loggers were taken to China (as checked baggage) with a set of 12 force balance accelerometers and a set of short signal cables. These loggers are synchronised to a fraction of a microsecond before a measurement then distributed over the bridge deck and towers in a sequence of measurements to record ambient vibration signals.
Some 14 separate measurements were made over a period of three days (25th-27th April 2017). For each measurement, the master logger was left recording vertical and lateral vibrations continuously at hanger locations H67 and H71 on the east walkway (there are 85 pairs of hangers each side) while other (slave) loggers were ‘roved’ to record for at least an hour synchronously at other locations on the east and west sides and inside the south tower.
The weather conditions were mostly benign; cloudy, cold, hazy and breezy on the first two days, clearing to a fine sunny day for the tower measurements. Due to pollution and unpleasant atmospheric conditions resulting from the heavily industrialised area around Jiangyin, team members wore protective face masks most of the time.
The second major technology being evaluated was the operational modal analysis planning and evaluation procedure developed by Professor Ivan Au as part of the BAYOMALAW collaboration with the University of Liverpool.
BAYOMALAW stands for ‘Bayesian operational modal analysis law’, and the main aim of the project is to establish uncertainty laws for modal testing to optimise tests such as these. BAYOMALAW aims to establish the best measurement configurations and the resulting uncertainties in modal parameters in terms of natural frequencies, damping ratios and mode shapes. Jiangyin is an extreme test because of its ultra-low natural frequencies and its weak lateral response buried in quasi-static effects of deck rotation.
As part of the procedure, a ‘huddle test’ is used to check the self-noise and environmental noise of the measurement system. To do this, all sensors are huddled into one location and sense either vertical or lateral vibrations simultaneously.
The exercise required a large investment of resource into building, programming, delivering and operating the system on site – but preliminary analysis of the data shows that the exercise was a success and that everything worked. The test was funded by the EPSRC and supported by Tongji University and JSTI.
Emperor House is a modern office building currently under construction at Exeter Business Park, UK. The three-storey building has an internal floor space of 2400sqm, which consists of two wings and a central core.
In collaboration with Summerfield Developments (SW) Ltd (client), WSP-Parsons Brinckerhoff (consultant) and Midas Group (contractor), the Vibration Engineering Section (VES) at the University of Exeter successfully carried out a test of the building’s dynamic properties and performance under human-induced excitation.
State-of-the-art equipment was utilised in the test to identify the modal properties of the first floor of the building and perform extensive walking tests.
The test results will be analysed in detail. The final aim is to help structural engineers to design such buildings at minimal cost, while vibration serviceability requirements are maintained.
Vibration Engineering staff led by Professor James Brownjohn have been awarded a £3.25m grant by EPSRC to create a new simulator facility for study of interactions between humans and the moving built environment. The simulator will use a mechanical hexapod to drive a 4 metre square platform in all 6 axes with accelerations and displacements representing typical movements of a range of civil structures (floors, footbridges, grandstands) where comfort of human users and occupants is critical.
The simulator will be fully instrumented with an array of force plates, inertial and optical motion capture and head mounted virtual reality for nine occupants.
This grant is part of a large investment by EPSRC and both Universities of Exeter and Bath; a University of Bath team let by Anthony Darby have simultaneously been awarded a £1.65m grant for a complementary simulator for study of large amplitude building sway at low frequencies typical of tall and super-tall buildings.
Co-funding from Universities of Bath and Exeter for infrastructure, additional equipment and staffing beyond the three year initial EPSRC funding amounts to £2.42m, and the total project cost will be £7.25m.
VSimulators will provide cross-disciplinary capability to address deficiency of information on human factors, environment and structure motion on engagement with the built environment:
- For slender sustainable structures, e.g. tall buildings, vibration serviceability is a critical design constraint poorly (if at all) addressed by design codes, hence a need for bespoke customised acceptance criteria.
- Effects of low level vibrations coupled with sound/noise, light, pollution, smell, temperature, humidity, and other environmental factors which contribute to the mysterious sick building syndrome.
- Mobility and rehabilitation in an aging population cost the National Health Service £bns per year. Rehabilitation of motion-impaired patients is a major problem.
The Exeter investigator team comprises:
James Brownjohn Principal Investigator, Structural Dynamics
Alex Pavic Co-Investigator, Vibration Serviceability
Paul Reynolds Co-investigator, Vibration Control
Vicki Goodwin Co-investigator, Healthcare, Rehabilitation
Mateusz Bocian Co-investigator, Virtual Reality
The Bath team comprises:
Antony Darby Principal Investigator, Structural Engineering
Sukumar Natarajan Co-investigator, Environmental Design
David Coley Co-investigator, Building Occupant Behaviour
Ian Walker Co-investigator, Environmental Psychology
A facility manager is being recruited to work with research and commercial users to maximise facility use. Experimental officers will manage operations at the Exeter and Bath sites, James Bassitt at Exeter will supervise the Bath EO.
The international advisory team are:
Kenny Kwok University of Western Australia
Tracy Kijewski-Correa University of Notre Dame
Yukio Tamura Tokyo Polytechnic University
Robert Brown Memorial University, Newfoundland
Industrial support for VSimulators is provided by AKT II, Arup, Atkins, Buro Happold, Emirates DNEC Engineering Consultants, Flint&Neill (now COWI), Foster and Partners, Swallow Acoustics Consultants (now part of Thornton Tomasetti), Waterman Structures and WSP|PB.
VSimulators is affiliated to UKCRIC and will be a national research facility available to RCUK-funded researchers for research projects as well as to private industry at commercial rates.
Links to publicity in national and local media can be found here.
The impact of vibrations from very tall buildings and wobbly bridges and floors on people’s health and wellbeing is to be researched in a new £7.2 million government-funded national research facility.
Check out the rest of the story about the launch of VSimulators on the University of Exeter’s website
In the meantime, here is some other coverage of the story:
Did you feel the earth move? (Source: The Plymouth Herald)
Do YOU work in a skyscraper? Wobbly high-rise buildings may trigger motion-sickness, insomnia and depression (Source: Daily Mail)
The result of many months’ work on an EPSRC funded project was revealed on 16th February at a launch event for a novel vibration control system. The event attracted directors, associates and senior engineers from major companies including WSP, Atkins, Foster and Partners and Arup. They witnessed the launch of a proof-of-product system, which was developed by Professor Paul Reynolds and Dr Emma Hudson to address the current gap between the proven academic successes of active vibration control for floor structures and the lack of adoption by industry to date.
The technology works in a similar way to that of popular noise-cancelling headphones: an accelerometer is used to measure the vibrations of the structure; the resulting signal is processed by a real-time computer and then an actuator generates the required force to cancel out the measured vibrations.
This new product combines all these components into one standardised compact unit that can be more easily installed within structures. Crucially, the system has been developed with robustness and minimised cost as priorities, to complement the proven high performance of this technology. In this way, the system is significantly more commercially attractive to potential adopters, meaning that the benefits of enhanced vibration performance are now a step closer to being realised.
A lunchtime seminar was organised at the Institute of Structural Engineers HQ in London to highlight the potential benefits of this new product to key industry contacts. A joint presentation by Paul Reynolds and Emma Hudson was followed by a live demonstration of the new system.
On Monday 5th December a team of researchers for the EPSRC STORMLAMP were flown from Castletown-Bearhaven, Ireland to Fastnet Rock, 6 miles off the Irish mainland.
James Bassitt, Karen Faulkner and Ian Moon from University of Exeter, along with Alessandro Antonini from Plymouth University and Athanasios Pappas from UCL planned to stay overnight after carry out a modal test of the lighthouse, while James Bassitt installed a remote acceleration monitoring system.
Following a series of modal tests on lighthouses at Les Hanois (Guernsey), Wolf Rock (Cornwall), Longships (Cornwall) and Bishop Rock (Scilly Isles), James, Ian and Alessandro had developed skills in modal testing using an array of accelerometers and an electrodynamic shaker. While these lighthouses are accessed via a helideck constructed above the lantern, Fastnet is accessed by a helipad on a utility building constructed on the cramped space of the rock with stone steps up to the lighthouse. A team of five was used at Fastnet to manage the equipment transfer to and from the upper level of the lighthouse and to allow James Bassitt to install and commission the monitoring system.
First measurements started at 2PM on Monday and continued until 9.30PM, with the APS shaker providing a narrow-band swept sine signal to excite structural modes that are typically in the range 4-6 Hz for this type of structure. The accelerometer array was left recording data overnight as storm winds and occasionally waves battered the lighthouse.
While on site James Bassitt deployed a drone for aerial footage at medium and close range.
Weather conditions of wind and sea spray overcame the drone after 11 minutes of flying the machine was returned to base with full manual control after which it was unserviceable. The short flight provided spectacular views of the rock and lighthouse.
Fastnet Rock is notorious for bad weather, particularly fog, hence its existence. From Tuesday 6th until Friday 9th fog was severe enough to prevent helicopter landing, stranding the team. While having more than the mandatory supply of emergency rations the team were very happy when a break in the fog allowed the pilot to make two trips to pick up crew and equipment. The Exeter team, who travel with the equipment by van and ferry arrived in Exeter late on Saturday 10th.
Without a retrofitted helideck, Fastnet Lighthouse is a relatively ‘clean’ structure for which to create a mathematical model. Using the experimental modal test data and masonry stiffness estimates obtained on site using a Schmidt Hammer UCL researchers on the STORMLAMP project will be able to create a high-fidelity model which is intended to be used to estimate wave loads using response data provided by the monitoring system.
Two more lighthouse modal tests are lined up for 2017; one is likely to be Dubh Artach off the Scottish West coast and Eddystone Lighthouse off Plymouth.
STORMLAMP researchers from Exeter and Plymouth concluded a sequence of measurements on an offshore rock lighthouse in the South West with a modal test of Bishop Rock lighthouse.
Bishop Rock is a massive structure, built on a rocks four miles south west of the Scilly Isles, that sheer from 45m deep in the Atlantic Ocean. The first structure, completed in 1858, was strengthened in 1881 by building a new structure around the existing lighthouse and extending the height by 12m to 44m above mean high water.
On a very wet and windy September Monday, James Bassitt, Ian Moon (Exeter ian_james_selfie.jpg) and Alessandro Antonini (ale_daq.jpg) flew from St Just (Land’s End) airport to carry out a sequence of vibration measurements using accelerometers aligned horizontally at the top of the lighthouse.
After an energetic exercise laying out, connecting and configuring the sensors, horizontal accelerations were measured in the lower entrance level, engine rooms, bedroom, kitchen, service and battery rooms, lantern level and helideck (ian_helideck.jpg).
Response due to ambient conditions of strong winds and relatively benign waves was measured, as well as the effect of artificial excitation using a 140 N electro-dynamic shaker (shaker.jpg). Measurements started at around 1PM and were completed within two hours.
Unfortunately, the strong winds were quickly followed by low visibility on Monday afternoon, shutting down Trinity House helicopter flights and stranding the team overnight. Happily the fog horn no longer operates at Bishop Rock, dining facilities were available (dinner.jpg) and the eerie effect of the powerful twin lantern beams
provided some entertainment. The team escaped when the fog lifted on the Tuesday afternoon.
The modal test data are being used to evaluate the structure and provide the means for inverse identification of wave loads. The next STORMLAMP mission will be to Fastnet Lighthouse in December.
The video is by Peter Cox a wonderful landscape photographer based in Ireland.