Pedestrian Interaction with Lively Low-Frequency Structures

The expectation for high-quality infrastructure and improved quality of life is at its highest point in contemporary society. At the same time the world is experiencing fast urbanisation, pressure on natural resources and ambitious requirements to provide a sustainable built environment. Structural engineers are responding by utilising high-strength materials and designing more efficient and lighter structures. Coupled with innovations in structural forms and aesthetics, all these factors lead towards lighter and therefore 'livelier' (i.e. more vibration prone) structures. Examples of known (lively) footbridges, building floors and staircases affected by excessive vibrations and unfit for the intended purpose are numerous, despite the tendency to keep the problematic cases far from the public eye due to damaging commercial reputations to those involved.

It is generally accepted now that vibration serviceability requirements are governing the design and determining the cost of these structures, many of which are exposed and suffer from the dynamic excitation induced by human walking. Publicity of the infamous excessive sway of the Millennium Bridge, London, under crowd loading ten years ago, and subsequent expensive retrofitting, demonstrated an urgent need to develop fundamental understanding of pedestrian behaviour on lively low-frequency structures. While research into pedestrian interaction with laterally swaying bridges has since intensified, the interaction with a more frequent class of structures that are prone to excessive vibrations in the vertical direction has been progressed little.

The aim of this project is to characterise the interaction between pedestrians and low-frequency structures that are lively in the vertical direction. The interaction occurs because humans are highly sophisticated and sensitive dynamic systems who react to and adapt to the surrounding (vibrating) environment. Current understanding of this phenomenon is limited and consequently it is ignored in design guidelines. However, it is this understanding that is necessary for achieving high-quality infrastructure fit for intended use. This project will make significant contribution in this direction through two novel developments:

I) A unique experimental facility consisting of a low-frequency structure and equipment for monitoring both human locomotion and the structural vibration will be developed. This will overcome the current lack of suitable facilities of this kind and it will enable the collection of a comprehensive set of data that characterises human behaviour on lively structures.

II) Based on experimental observations, a numerical model of the interaction between humans and the structure will be developed.

The outputs of this project will significantly enhance understanding of structural vibration performance in operating conditions leading to more efficient and controllable design.

Although this two-year project will be focussed on studying the human-structure interaction, the facility to be developed will represent an essential experimental platform for future multidisciplinary research collaborations. This will extend the legacy of this project beyond the date of its completion.

The proposed research programme will provide new and comprehensive insights into human interaction with vibrating low-frequency structural environments. This will be achieved through designing a unique experimental facility and acquiring a novel set of data to enable mathematical modelling of the interaction. This new knowledge will be disseminated through journal and conference publications, a website devoted to the project, seminars at the host organisation and at industrial sites, a workshop for students, collaborative contacts with other researchers, and participation in events organised by professional bodies.

The deliverables of this project will open exciting new prospects for the construction industry to improve the understanding of human interaction with structural vibration in the vertical direction and help them deliver high-quality infrastructure fit for intended use. Given the traditional interest and high-level of expertise of the UK industry in this field of structural engineering, it is expected that the new knowledge will provide a further competitive edge on the international market and support the industry's leading position in the field. This expertise will be increasingly important due to widespread use of light construction materials and their sensitivity to dynamic loadings. If the indications of the previous research are confirmed - that the interaction has a beneficial effect on the structure in form of lower-than-expected vibration response - this will open new opportunities for more efficient and cost effective design of footbridges and low-frequency floors. The structural engineering community within the industry will also benefit from the knowledge transfer from the area of biomechanics, normally not easily accessible to structural engineers.

Other beneficiaries of this research are professional and other bodies developing design regulations. Better guidance is essential to achieve structures with optimum vibration performance, and therefore the update of current out-of-date guidelines concerned with footbridge design, such as BS5400, is of crucial importance. Exceptional interest of regulatory bodies to incorporate latest research findings in design for vibration serviceability in their guidelines already exists, as recently demonstrated by IStructE who issued new guideline for design of grandstands (``Dynamic Performance Requirements for Permanent Grandstands Subject to Crowd Action: Recommendations for Management, Design and Assessment'', 2008) based on recent research into interaction between jumping people and flexible structures, as well as by British Standards Institution which is monitoring closely the research developments concerned with the interaction on footbridges (``Background to the National Annex to BS EN 1991-2: Traffic Loads on Bridges'', PD 6688-2 draft document, 2010).

Broader research community (both in industry and higher education institutions) will benefit from the access to the new data, knowledge and facilities created during the course of this project. This will enable fostering long-term collaboration on a variety of future projects, prolonging the impact of this research well beyond the date of its completion. The research topics that will build on successful completion of this project include: human perception of vibration while walking on low-frequency structures, effectiveness of damping devices in attenuating walking-induced vibrations, dynamic properties of pedestrians, crowd management on lively structures and modelling multi-person traffic.

New more sophisticated design and timely preventions of vibration serviceability failures will contribute to enhancing quality of life of end structural users (public). Society in general will benefit from new knowledge in structural design thorough education of generations of UG students and PG researchers, and efficient and safe design of new structures. These are important components of sustainable development.