Advanced Measurement, Modelling and Utilisation of Bouncing and Jumping Loading Induced by Groups and Crowds

Prediction of dynamic loads induced by groups or crowds of people remains one of the most significant problems faced by designers of vibration-sensitive structures such as footbridges, dance floors, grandstands and staircases. Structural engineers understand other key dynamic loads, such as seismic and wind, comparatively well due to decades of research leading to comprehensive and robust guidance, but understanding of dynamic loads due to multiple active people lags by several decades. The lack of understanding and resulting inadequate guidance not only leads to economic costs and unnecessary carbon emission but also results in safety concerns related to crowd panic due to unexpected and unfamiliar structural motion induced by occupants. Moreover, design mistakes of highly visible landmark structures, such as sport stadia and footbridges in urban environments, attract significant publicity (e.g. London Millennium Bridge and Cardiff Millennium Stadium) and a bad reputation for their designers and the construction industry.

The aim of this project is to improve the fundamental understanding of group and crowd loading due to bouncing and jumping. This will be addressed through the following three developments:

1. Establishing a unique database of bouncing and jumping loads generated by groups of various sizes. The project aims to address this challenge by a novel experimental approach which combines laboratory and field studies of directly measured loads and tracking motion of each group member. This requires a cross-disciplinary approach, with deep understanding of motion tracking, computing and a comprehensive range of hardware.

2. Developing a new generation of data-driven, statistically reliable and practicable models which can predict reliably the effect of jumping and bouncing groups and crowds on civil structures. As vibration serviceability criteria governs modern design, a key goal of the project is to provide analytical tools for a time efficient probability based vibration serviceability assessment of a structure at the design stage. Such tools will help to achieve a perfect balance between dynamic performance, associated risk and uncertainty, aesthetics, cost and carbon footprint of a future structure.

3. Providing a solid platform for development of scientifically rational design guidance for vibration serviceability assessment of structures under jumping and bouncing crowd excitation, which is not overly conservative as a result of uncertainties in the loading. The latest design guidance on crowd dynamic loading of grandstands was published in 2008, so the timing of the project is perfect. The UK leads internationally in design for vibration serviceability with growing international acceptance of UK-originated guidance and the ultimate aim of the project is to maintain this leadership.

Results will impact not only understanding of how active people affect dynamic performance of structures but will also benefit the wider communities where human periodic activities are important, such as psychology of mass behaviour and public safety.

Being concerned with the quality of accommodation as well as safety and well-being of the public members using assembly structures, civil structural engineering usually adopts a conservative approach when designing for dynamic loads which are not well understood, such as the case with group/crowd bouncing and jumping loads (G/CBJL). The less a particular structural loading is understood, the more conservative the design to resist it becomes. Therefore, improved fundamental understanding of G/CBJL would have potentially profound effects on the economy of the design and is the key deliverable of the First Grant against which its economic impact should be judged. Bearing in mind that civil structural engineering research is applied science aimed at improving publicly available design guidelines and quality of life, a project of this kind has little difficulty justifying its potential societal impacts. Moreover, this is an area with obvious potential for a range of interdisciplinary research engagements addressing issues beyond structural dynamics, such as psychology of mass behaviour and public safety, thus having potential for a wider academic impact.

Due to considerable improvements in the quality and strength of modern construction materials, it is common nowadays that human induced dynamic loading governs the design of long-span building floors, footbridges, staircases and grandstands (i.e. determines sizes of structural elements such as beams and columns, including expensive foundations and their depth). When a conservative design approach is adopted, this invariably means considerably greater weight, cost and carbon footprint of assembly structures. A recent report by The Royal Academy of Engineering (King 2010) clearly states that the UK will not be able to achieve its target of reducing carbon emissions by 80% by 2050 unless it urgently addresses carbon emissions from the built environment. In addition, a study published in the New Civil Engineer on 1 October 2009 showed that more than half of the construction carbon footprint of a building comes from the construction of its bare structure, which is a staggering one sixth of the total carbon footprint during the life of a building. This indicates the huge importance of designing realistically new structures. Non-rational overdesign of structural elements using arbitrary rules of thumb to satisfy dynamic performance requirements under group/crowd dynamic loading can easily result in overall structural weights which are 25% greater than necessary. On the other hand, in the cases when effects of group/crowd dynamic loading were ignored, unwarranted design assumptions made and boundaries of high slenderness pushed by daring architects and their structural engineering consultants, vibration serviceability failures have occurred at great cost, as was the case with the London Millennium Bridge and Cardiff Millennium Stadium.

With regard to vibration serviceability, the UK has always been at the forefront of its research and application developments. Over the last 40 years, this country has been ahead of the USA and rest of the world and maintained the most advanced design guidelines dealing with vibration serviceability. A key objective of the First Grant is to maintain and enhance this strategic lead. Its results will feed quickly into the publicly available UK design guidelines pertinent to human-induced dynamic loading; relevant Government departments, such as the DCMS and the Highways Agency, as well as the ICE and IStructE will be appraised of the developments in the research and made aware of the results of the research. Society ultimately benefits from more efficient structures with reduced carbon footprint, with healthier, safer and more comfortable environments for spectators, audiences and active occupants.

Reference:
King D (2010) Engineering a low carbon built environment. Royal Academy of Engineering, London, United Kingdom.