Aeroelastic and Non-linear Structural Dynamic Interactions of Slender Structures

Lead Research Organisation: University of Bristol
Department Name: Civil Engineering

Abstract

As more slender and more adventurous structures, such as cable-stayed bridges, are constructed, they become increasingly susceptible to large amplitude vibrations, particularly due to aerodynamic loading. Wind-induced vibrations of bridge decks, cables, towers, lamp columns and overhead electricity cables are indeed very common. This can lead to unacceptably large movements, direct structural failure, or dangerous long-term fatigue damage of structural components. Complex interactions between the wind and the structure and also between different components of the structure (e.g. cables and bridge deck) can lead to vibration problems, so for proper understanding of the behaviour, both aerodynamic and structural effects need to be considered.Whilst some of the mechanisms of wind loading of structures are reasonably well understood, others are not, and many instances of vibrations, particularly of cables, are not well explained. Recent work has developed a generalised method for analysing 'galloping' vibrations. These are caused by changes in wind forces on a structure when it starts to move, which actually tend to increase the motion. For typical bridge cables (or other similar size structures) in moderately strong winds, a particular change in the wind flow around the cable occurs, known as the drag crisis. This changes the forces on the cable and causes a special case of galloping-type vibrations, which the new method of analysis is able to predict, for the first time. Comparisons of these calculations with wind tunnel test results on inclined cylinders have confirmed that the basic method does work, but there is a need to consider additional effects, such as wind turbulence, torsional motion of the structure and more accurate account of the changes in the aerodynamic forces as the structure moves. It is proposed to develop the approach to include these effects, using further wind tunnel data, to eventually create a unified framework for wind loading analysis of any real structure for galloping, together with the other aerodynamic mechanisms buffeting (due to wind turbulence) and flutter.Meanwhile, interactions between vibrations of structural components can cause serious effects. For example, very small vibrations of a bridge deck can cause very large vibrations of the cables supporting it, through the mechanism of 'parametric excitation'. Even more surprisingly, in other instances, localised cable vibrations can lead to vibrations of the whole structure. Research under another grant is already considering these effects for very simplified structures, but it is proposed to extend the analysis to realistic full structures. Also, often cables are tied together to try to prevent vibrations of individual cables, but they can then all vibrate together as a network. This project therefore aims to analyse full cable networks, to understand how their vibrations can be limited.Finally, it is proposed to bring together the above two main areas, to include both aerodynamic and structural dynamic interactions in the analysis of slender structures. For example, because of the interactions, the wind loads on relatively small elements, such as cables, can have surprisingly large effects on the overall dynamic response of large structures. At present this is generally ignored, but the joint approach will address this issue. Also, in some instances, only a combined view of the phenomena may be able to explain the behaviour observed on full-scale structures in practice. The holistic view of the wind loading and structural behaviour should provide tools to help avoid undesirable and potentially dangerous effects of vibrations of slender structures in the future. Based on the analysis, this could be achieved by modifying the shape of the elements to change the wind loads, or introducing dampers to absorb enough vibration energy.

Publications


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Zhang J (2010) Identifying Bridge Aeroelastic Parameters from Full-scale Ambient Vibration Data in Proceedings of the 9th UK Conference on Wind Engineering
Tzanov V (2011) Internal resonance between in-plane and out-of-plane modes of vibration of inclined cables subjected to vertical support excitation in Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011
Symes JA (2007) The effects of small-scale wind turbulence on dry inclined cable galloping in Proceedings of the 12th International Conference on Wind Engineering
Symes JA (2007) Combined buffeting and dry galloping analysis of inclined stay-cables in Proceedings of the 7th International Symposium on Cable Dynamics
Nikitas N (2009) Wind tunnel testing of an inclined aeroelastic cable model - Pressure and motion characteristics, Part I in Proceedings of the 5th European and African Conference on Wind Engineering
Nikitas N (2008) Full-scale identification of modal and aeroelastic parameters of the Clifton Suspension Bridge in Proceedings of the 6th International Colloquium Bluff Body Aerodynamics and Applications
Nikitas N (2015) Aerodynamic forcing characteristics of dry cable galloping at critical Reynolds numbers in European Journal of Mechanics - B/Fluids
Nikitas N (2014) Misconceptions and Generalizations of the Den Hartog Galloping Criterion in Journal of Engineering Mechanics
Nikitas N (2010) The Den Hartog galloping criterion revisited: a non classical case in Proceedings of the 9th UK Conference on Wind Engineering
Nikitas N (2012) Excitation characteristics of dry galloping vibrations in Proceedings of the 10th International Conference on Flow-Induced Vibration
Merce RN (2007) Finite element model updating of a suspension bridge using ANSYS software in Proceedings on the Symposium on Inverse Problems, Design and Optimization
Massow CLS (2007) Theoretical and experimental identification of parametric excitation of inclined cables in Proceedings of the 7th International Symposium on Cable Dynamics
Marsico MR (2011) Nonlinear cable vibrations: experimental tests on an inclined cable in Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011
Macdonald JHG (2014) Response amplitudes of non-linear stay cable vibrations in Proceedings of the Symposium on the Dynamics and Aerodynamics of Cables
Macdonald JHG (2008) Large-scale wind tunnel tests of inclined cable vibrations - Preliminary findings in Proceedings of the 8th UK Conference on Wind Engineering
Macdonald J (2008) Pedestrian-induced vibrations of the Clifton Suspension Bridge, UK in Proceedings of the Institution of Civil Engineers - Bridge Engineering
Macdonald J (2010) Dynamic excitation of cables by deck and/or tower motion in Proceedings of the Institution of Civil Engineers - Bridge Engineering
Macdonald J (2011) JWEIA foreword to WES-2010 special issue in Journal of Wind Engineering and Industrial Aerodynamics
Macdonald J (2008) Two-degree-of-freedom inclined cable galloping-Part 1: General formulation and solution for perfectly tuned system in Journal of Wind Engineering and Industrial Aerodynamics
Macdonald J (2008) Two-degree-of-freedom inclined cable galloping-Part 2: Analysis and prevention for arbitrary frequency ratio in Journal of Wind Engineering and Industrial Aerodynamics
Macdonald J (2008) Lateral excitation of bridges by balancing pedestrians in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Macdonald J (2009) Discussion: Pedestrian-induced vibrations of the Clifton Suspension Bridge, UK in Proceedings of the Institution of Civil Engineers - Bridge Engineering
Macdonald J (2012) Briefing: Current trends in engineering mechanics: structural dynamics in Proceedings of the Institution of Civil Engineers - Engineering and Computational Mechanics
Macdonald J (2010) Generalised modal stability of inclined cables subjected to support excitations in Journal of Sound and Vibration
Liu X (2013) Kinetic analysis and rehabilitation of old bascule bridge in Tianjin, China in Proceedings of the Institution of Civil Engineers - Bridge Engineering
Jakobsen JB (2009) Wind tunnel testing of an inclined aeroelastic cable model - Pressure and motion characteristics, Part II in Proceedings of the 5th European and African Conference on Wind Engineering
Jakobsen J (2012) Wind-induced response and excitation characteristics of an inclined cable model in the critical Reynolds number range in Journal of Wind Engineering and Industrial Aerodynamics
He M (2013) The potential for classical galloping of a nominally smooth circular cylinder - a special case in Proceedings of the 6th European and African Conference on Wind Engineering
Gonzalez-Buelga A (2008) Modal stability of inclined cables subjected to vertical support excitation in Journal of Sound and Vibration
Gonzalez-Buelga A (2008) Cable-bridge-deck interaction modelled via real-time dynamic substructuring in Proceedings of the 7th European Conference on Structural Dynamics, EURODYN 2008
Falcao Silva MJ (2007) Tuned Liquid Dampers for reducing building vibrations in Proceedings of the 7th Portuguese Congress of Seismology and Earthquake Engineering, SISMICA 2007
Bocian M (2011) Modelling of self-excited vertical forces on structures due to walking pedestrians in Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011
Andersen TL (2009) Drag-crisis response of an elastic cable-model in Proceedings of the 8th International Symposium on Cable Dynamics
Acampora A (2011) Identification of aeroelastic forces on bridge cables from full-scale measurements in Proceedings of the 4th International Conference on Experimental Vibration Analysis for Civil Engineering Structures
 
Description 1. The mechanism of human-structure interaction leading to detrimental large amplitude vibrations of bridges, such as occurred on the London Millennium Bridge.
2. Increased understanding of the mechanisms of aerodynamic excitation of cables on cable-stayed bridges which can lead to large amplitude vibrations and hence fatigue failure of cables.
3. Increased understanding of the interaction between the vibrations of bridge decks (e.g. due to wind or traffic) and cables on cable-supported bridges, which can also lead to large amplitude vibrations and hence fatigue failure of cables. A method for estimating the amplitudes of cable vibrations.
Exploitation Route The work on human-structure interaction could be developed to address other scenarios, such as dynamic excitation of stadia due to crowds. This work also concerns human balance so has the potential to inform work on reducing the risk of falls, particularly in the elderly.
Sectors Construction,Healthcare,Transport
 
Description 1. Some of the findings have been incorporated in the Post Tensioning Institute (PTI) Recommendations for Stay Cable Design, Testing and Installation. The PTI is based in the USA and its recommendations are used internationally. 2. Results are being used by consulting engineers in the UK, Canada and possibly elsewhere.
First Year Of Impact 2008
Sector Construction
Impact Types Cultural,Societal
 
Description Membership of the working group on updates to the Eurocode on Wind Actions in Structures.
Geographic Reach Europe 
Policy Influence Type Membership of a guideline committee
 
Description Newton Research Collaboration Programme
Amount £20,000 (GBP)
Funding ID NRCP/1415/292 
Organisation Royal Academy of Engineering 
Sector Learned Society
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 03/2015 
End 12/2015
 
Description DTU Cable aerodynamics 
Organisation Technical University of Denmark
Country Denmark, Kingdom of 
Sector Academic/University 
PI Contribution Scientific Advisor to Technical University of Denmark project on "Understanding and controlling wind-induced vibrations of bridge cables" funded by Femern A/S and Storebælt A/S. Advised on wind tunnel testing and site monitoring and more specifically supervised analysis of the site data.
Collaborator Contribution Built a new wind tunnel and conducted static and dynamic wind tunnel tests on dry, wet and iced cables. Installed monitoring systems on the Storebælt and Øresund Bridges. The collaboration has led to greater understanding of the mechanisms of wind excitation and hence means to reduce the vibration amplitudes of cables. This is important to prevent fatigue failure of the cables, enhancing the safety and reducing the maintenance liability of major bridges.
Impact One journal paper and one conference paper on analysis of the site data.
Start Year 2008
 
Description NRC Cable aerodynamics 
Organisation University of Stavanger
Country Norway, Kingdom of 
Sector Academic/University 
PI Contribution Contribution to the design of wind tunnel tests on inclined cable models and analysis of the data.
Collaborator Contribution National Research Council of Canada (NRC) - Conducted the wind tunnel tests Federal Highway Administration - Provided funding for tests at NRC University of Stavanger - Also contributed to the design of the tests and analysis of the data
Impact Numerous papers on the aerodynamics and wind-induced vibrations of inclined cables for cable-stayed bridges, with and without the addition of helical fillets on the surface. The collaboration has led to greater understanding of the mechanisms of wind excitation and hence means to reduce the vibration amplitudes of cables. This is important to prevent fatigue failure of the cables, enhancing the safety and reducing the maintenance liability of major bridges.
 
Description TV and radio interviews on the Millennium Bridge problem 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Interviews with BBC TV News, BBC Radio 4, Radio 5 Live, Radio London, Radio Bristol, BBC World Service and ITN Evening News and articles in The Times, Independent, Telegraph and Daily Mail on research findings of the mechanism of dynamic excitation of footbridges by pedestrians, as occurred on the London Millennium Bridge on its opening day. The media interviews coincided with the publication of a paper in Proc. Royal Society A. The intended purpose was to enthuse the public about engineering, giving a positive image of engineering being about problem solving, rather than the negative image many had following the vibration problem on the bridge and its closure when it was first opened. It is difficult to quantify the impacts except that I subsequently received many inquiries about the research, from both the public and some practising engineers.
Year(s) Of Engagement Activity 2008