Table Of ContentThe Institution of Structural Engineers
The Department for Communities and Local Government
The Department for Culture Media and Sport
December 2008
Dynamic performance
requirements for permanent
grandstands subject to
crowd action
Recommendations for management,
design and assessment
Published by the Institution of Structural Engineers
Membership of the Joint Working Group
Dr J W Dougill – Chairman
Professor A Blakeborough – Oxford University
Mr P Cooper – KW Ltd to July 2007, then INTEC
Dr S M Doran – IStructE, Secretary
Dr B Ellis – BRE to 2006 now Consultant
Mr P F Everall – DCLG (to 2005)
Dr T Ji – UMIST/ The University of Manchester
Mr J Levison – Football Licensing Authority, d. 12th Dec. 2007
Dr J Maguire – Lloyd’s Register. (received papers from 2002)
Mr S Morley – Bianchi Morley
Mr M Otlet – W S Atkins
Professor G A R Parke – Surrey University (to 2002)
Mr J. G. Parkhouse – Parkhouse Consultants
Professor A Pavic – The University of Sheffield
Mr L Railton – Health and Safety Executive (to 2003)
Mr W Reid – Consultant, URS
Mr R Shipman, DCLG, (from 2005)
Mr P Westbury – Buro Happold. (received papers from 2002)
Mr M Willford – Ove Arup
Professor J Wright –The University of Manchester/J2W Consulting Ltd
Corresponding Members
Mr D Allen, National Research Council of Canada
Dr M Kasperski, Bochum University
Dr P Reynolds, The University of Sheffield
Mr P Wright, Health and Safety Executive, from 2003
Contributors
The Joint Working Group wishes to acknowledge the contribution of the following individuals who, though
not attending as members of the Group, made presentations on different aspects relating to grandstand
design, operation and behaviour.
Mr D Allen, National Research Council of Canada
Mr J Cutlack, J. Bobrowski and Partners
Dr J Dickie, Crowdsafe Ltd
Mr C Gleeson, Chelsea Football Club
Professor M J Griffin, Institute of Sound and Vibration, Southampton University
Dr M Kasperski, Bochum University, Germany
Dr J Littler, BRE
Dr A J Soane, Bingham Cotterell
Published by the Institution of Structural Engineers
International HQ, 11 Upper Belgrave Street, London SW1X 8BH, UK
ISBN: 978-1-906335-12-0
© 2008: The Institution of Structural Engineers
The Institution of Structural Engineers, DCLG, DCMS and the members who served on the Joint Working Group
which produced this report have endeavoured to ensure the accuracy of its contents. However, the guidance and
recommendations given in the report should always be reviewed by those using it in the light of the facts of their
particular case and specialist advice obtained as necessary. No liability for negligence or otherwise in relation to this
report and its contents is accepted by the Institution, the members of the Joint Working Group their servants or agents.
Any person using this report should pay particular attention to the provisions of this Condition.
No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means
without prior permission of the Institution of Structural Engineers, who may be contacted at 11 Upper Belgrave Street,
London SW1X 8BH.
ii Dynamic performance requirements for permanent grandstands subject to crowd action
FOREWORD
The Joint Working Group met first in January 2000. Its Interim Guidance was published in
November 2002 in response to concerns over crowd action on structures generally and on the
relevance of available recommendations to dense crowd loading on permanent grandstands. The
Interim Guidance used the vertical natural frequency, for the mode of vibration that could be
excited and felt by people on the seating deck, as the currency to determine different categories
of permissible use. No attempt was made to recommend a method of estimating performance by
calculation as it was considered that existing procedures, though widely used, could not be relied
on. The Interim Guidance was designed to be safe and straightforward to apply. It provided a
significant relaxation of the ‘trigger value’ frequency limits of BS6399 (1996) and the 1997 Green
Guide. However, because of the simplification of using natural frequency as the single factor
determining a category of use, it was a broad brush treatment. What was needed was a method
of design and operation that was based on an estimate of performance that was reasonable when
compared with the effects observed with active crowds in real structures. This was the task of the
Joint Working Group from 2002 onwards.
In addressing the technical issues relating to the analysis of the structure, the Joint Working
Group has been closely involved with a number of UK research projects (almost all supported
by the Engineering and Physical Sciences Research Council, EPSRC) that have been undertaken
since 2000 and which have contributed to an improved understanding of the physical problem of
how human beings interact with moderately flexible structures. This work has provided the basis
for the technical content in the new Recommendations. However, this could not be seen as an end
in itself. A key issue in design is how to deal with uncertainty. With grandstands, there can be no
absolute certainty on the way any random group of people will behave. Accordingly, the technical
provisions have been set in a framework of procurement, management and operation aimed at
minimising risk by managing uncertainty.
The Recommendations propose that specially ‘Listed Engineers’, having particular
experience and capability, be used in the design and assessment of grandstands for dynamic
crowd loading. Design should be based on the concept of managed events described by standard
Design Event Scenarios that form part of the specification for a stand. Within these scenarios, the
Management of the facility takes responsibility for specific agreed measures to mitigate the effects
of motion. Hand-over procedures are outlined with the aim of ensuring that the design calculations
relate to the as-built structure. The aim of each of these recommendations is to reduce uncertainty
where it is possible to do so.
The Recommendations are written for everyone who has responsibility for grandstands. This
includes the owners, operators, managers, architects, insurers and engineering designers as well as
Local Authority staff dealing with building control and safety issues. The Recommendations are
accompanied by Appendices directed particularly at the engineering analyst and designer.
The Recommendations relating to specification, management and operation should be
considered to be of equal importance to providing comfort and safety as the technical guidance
addressed principally to the engineering designer.
Dr John W Dougill
December 2007
Dynamic performance requirements for permanent grandstands subject to crowd action v
Contents
Foreword v
1 Scope of the Recommendations 1
2 Design event scenarios 2
3 Listed Engineers 4
3.1 Requirement for specialist engineering expertise 4
3.2 Technical support 4
3.3 Discretion on relevance of the Recommendations to specific structures 4
3.4 Judgment on relevance of the Recommendations to specific structures 4
3.5 Monitoring 5
4 Natural frequencies and other dynamic properties 6
4.1 Background 6
4.2 Structural modelling to determine modal properties of the
empty grandstand 6
4.3 Values for initial design 7
4.4 ‘Relevant’ natural frequency 7
5 Testing 8
5.1 Need for testing 8
5.2 Aims of testing 8
5.3 Circumstances requiring testing 8
6 Management responsibilities 10
6.1 Overall responsibility 10
6.2 Design of new stands 10
6.3 Change of use and assessment for specific events 10
6.4 Operational strategies to reduce dynamic response and crowd alarm 11
6.5 Handover of new and structurally modified grandstands 12
6.6 Operations Manual 12
6.7 Operation 13
7 Route 1: Compliance with natural frequency requirements 15
7.1 Vertical excitation 15
7.2 Side-to-side horizontal excitation 15
7.3 Nodding modes due to front-to-back excitation 15
8 Route 2: Design for managed events 17
8.1 Outline 17
8.2 Idealised description of crowd activity 17
8.3 Serviceability: Tolerance of motion 18
8.4 Serviceability: Displacement limits 18
8.5 Ultimate load capacity 18
8.6 Fatigue 18
9 Analysis of dynamic performance 19
9.1 Impulse loads 19
9.2 Horizontal loads due to periodic excitation 19
9.3 Analysis for vertical periodic excitation 19
9.4 Human structure interaction 19
10 Use of the Recommendations 21
Dynamic performance requirements for permanent grandstands subject to crowd action iii
Appendix 1 Background to human structure interaction 22
A1.1 Introduction 22
A1.2 Basic principles 22
A1.2.1 Modelling human structure interaction 22
A1.2.2 Active and passive behaviour 23
A1.3 Application of the theory 23
A1.3.1 Direct application of the theory 23
A1.3.2 A pproximate analysis using an assumed mode shape for
the crowd’s motion 24
A1.4 Body Unit properties and loadings 24
A1.5 Analysis and results 24
A1.5.1 Modal analysis 24
A1.5.2 Root mean square (RMS) accelerations and acceleration limits 24
A1.5.3 Analysis with a dominant mode. 25
A1.5.4 Multi-mode analysis 25
A1.6 References 26
Appendix 2 Body unit properties and recommended loading 27
A2.1 Body unit and structure 27
A2.2 Crowd body elements 27
A2.3 Representation of periodic loading 28
A2.4 Internal ‘drivers’- G – producing dynamic crowd loading 29
i
A2.5 The crowd effectiveness factor ‘t’ 30
A2.5.1 Scenario 4 30
A2.5.2 Scenarios 2 and 3 30
A2.6 Monitoring and back analysis 31
A2.7 References 32
Appendix 3 Calculation of modal properties 33
A3.1 Introduction 33
A3.2 Modal analysis and natural frequencies 33
A3.3 Basic errors: two prime suspects 35
A3.3.1 Distinction between force and mass 35
A3.3.2 Stiffness 35
A.3.4 Methods for calculation of natural frequencies 36
A3.4.1 General comment 36
A3.4.2 Approximate analysis 36
A3.4.3 Computer based analysis 36
A3.5 Consequences of mistaken idealisations 36
A3.6 Comment 37
A3.7 Further information 38
Appendix 4 Dynamic testing of grandstands and seating decks 39
A4.1 Introduction 39
A4.2 What should be tested and what results are needed? 39
A4.3 Analysis and testing 40
A4.4 Principles of dynamic testing 41
A4.5 Excitation sources and testing techniques 43
A.4.5.1 Ambient vibration survey (AVS) 43
A.4.5.2 Heel-drop testing 43
A.4.5.3 Measured impact testing 43
A4.5.4 Shaker testing of different types and complexity 44
A.4.5.5 Future developments 45
A4.6 Specification and procurement 45
A4.7 Reporting 47
A4.8 Further Information 47
Appendix 5 Bibliography 48
iv Dynamic performance requirements for permanent grandstands subject to crowd action
1 Scope of the Recommendations
The Recommendations given here are for use in the design or assessment of permanent
grandstands and relate solely to dynamic action due to crowd activity. Reference should
be made to other guidance and relevant Standards for other load cases and design
requirements.
The Recommendations also include guidance relating to Management’s role in
design and in implementing operational requirements for stands being used for events
at which dynamic crowd loading can be expected. This guidance is concerned only with
those aspects of crowd management that directly influence the structural response of a
grandstand and so supplement, but do not replace legal and Standards’ based requirements
for safe operation. The operational arrangements adopted should be taken into account by
those undertaking an overall risk assessment at the scheme design stage or for a specific
event.
The Recommendations apply to grandstands with seating decks constructed in
structural steel, reinforced or prestressed concrete and combinations of these forms of
construction. No recommendations are made for the use of subsidiary systems to provide
additional damping or active control.
The Recommendations are considered relevant to grandstands with seating decks
having a supported span greater than 6m or cantilever spans of more than 2.5m. However,
it is recognised that, even within the declared scope of these Recommendations, there may
be particular grandstands for which the layout, form of construction or limited use might
render it unnecessary to undertake a full check on dynamic performance. The manner in
which this can be dealt with is treated in Section 3 on Listed Engineers.
The Recommendations revise and extend the recommendations given in the November
2001 report ‘Dynamic performance requirements for permanent grandstands subject to
crowd action: interim guidance on assessment and design’, published by the Institution of
Structural Engineers and adopted by DCLG and DCMS. This Interim Guidance used the
vertical natural frequency of the empty grandstand as the sole criterion for assessing the
acceptability of grandstands for use with crowds likely to generate dynamic loading. This
convenient, but coarse grained, approach is retained as an option in the present guidance
which now provides an alternative approach that depends on engineering estimates of the
likely performance of a grandstand for events at which the event organiser is responsible
for specific agreed measures relating to crowd management. This alternative approach
provides further options for the designer and management as well as addressing a need to
account for influences on behaviour additional to natural frequency.
As a consequence of this approach, there are two Routes available for design and
assessment of grandstand structures subject to dynamic crowd loading,
• Route 1: Based on limiting values of natural frequency for the grandstand empty of
people.
• Route 2: Based on estimates of performance of grandstands calculated for specified
managed events.
A grandstand may be considered to meet the Recommendations for dynamic crowd loading
if the requirements of either one or other of these routes are met together with the separate
conditions for horizontal strength and stability. (See Sections 7.2, 7.3 and Table 2).
Dynamic performance requirements for permanent grandstands subject to crowd action 1
2 Design Event Scenarios
The Design Event Scenario forms the basis for a design specification for dynamic
performance of a grandstand under crowd loading. Table 1 gives standard Design
Event Scenarios for use in communicating design objectives in terms of anticipated
performance.
The Table shows a range of different events together with the expected activity of
the crowd and an indication of crowd control measures to be provided by the management
of the grandstand.
The four performance based scenarios (numbered 1 to 4) correspond to increasing
crowd involvement and activity together with increased loading. Scenarios 1 and 2,
appropriate for viewing sporting events and classical concerts, would normally be satisfied
by Route 1 requirements. Scenario 3 refers to lively concerts and high profile sporting
events whilst Scenario 4 is for high energy events such as pop/rock concerts. The Scenarios
are provided in order to assist event specific assessment and to provide a yardstick for
authorities concerned with safety certification.
It will be evident that the Design Event Scenario is the statement of what should
be covered in design and what needs to be managed. The Scenario comprises a reference
to the category of event in Table 1 with a statement of any additional specific crowd
control measures that have been agreed as being required. (See Section 6.4 on Operational
Strategies).
It should be noted that the descriptions of exemplar events are indicative rather
than prescriptive. For example, an event may be described as a pop-concert for publicity
purposes but the crowd’s reaction may be only moderate and so more consistent with a
concert with medium tempo music as envisaged for Scenario 3. Accordingly, in using
records of past events to assist an assessment for a future event, care should be taken to do
this on the basis of observed performance and not solely on a record that a ‘pop-concert’
had been run satisfactorily in the past. (See Section 6.7 on Operation, re. record keeping).
The Scenarios are based on experience of events in the United Kingdom. In assessing
any specific event, judgment will be needed to decide the appropriate category particularly
between Scenarios 3 and 4 and, on occasion, whether the crowd at a particular sporting
event is likely to be more than usually active with coordinated rhythmic activity. This
has become common at football matches in mainland Europe where groups of fans have
rehearsed bobbing, treading or stamping in time to a beat provided by their leader. The
improved coordination accompanying behaviour of this sort can lead to motion that is more
severe than that anticipated for Scenario 4. This could lead to possible discomfort for seated
or standing fans not participating in the activity. Such situations need to be recognised and
appropriate operational measures adopted by Management. (See Section 6.4 on Operational
strategies).
2 Dynamic performance requirements for permanent grandstands subject to crowd action
D
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re Table 1 Event Scenarios to be supplemented with a statement on agreed operational arrangements
q
u Scenario Exemplar event Crowd behaviour Management Acceptance criteria
ire
m Expected crowd make up Stewarding Crowd expectation Natural frequency or
e design acceleration
n
ts limit
f
o 1 Stand used for viewing of Normally relaxed Predominantly seated Stewards require to Comfort Route 1 with 3.5 Hz
r
p sporting and similar events viewing public with be instructed as to min. or accepted at
e
r with less than maximum spontaneous response the possible effects the discretion of a
m
a attendance to single events of motion of the Listed Engineer
n
e structure resulting
n from coordinated
t g 2 Classical concert and Audience seated with Predominantly seated crowd activity and, Route 1 with
ra typical well attended only few exceptions – Comfort 3.5 Hz min. Is
particularly for
n sporting event minor excitation normally adequate
d Scenarios 3 and 4,
s but otherwise
ta need to be provided
n Route 2 and 3%g max.
d with the means for
RMS acceleration
s s instant communication
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b with central control.
je 3 Commonly occurring Potentially excitable All standing and A few individuals may Route 1 with 6 Hz min.
c
t events including, inter alia, crowd with crowd participating during some complain at lack of Otherwise Route 2,
to high profile sporting events participation part of the programme comfort but most will and 7½%g max. RMS
c and concerts with medium tolerate the motion acceleration
ro
w tempo music and revival
d pop-concerts with cross
a generation appeal
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4 More extreme events Excited crowd, mostly Mainly young Excitement and Route 1 with 6 Hz min.
including high energy standing and bobbing and active with motion but with Otherwise Route 2,
concerts with periods of with some jumping vigorous participation expectation of and 20%g max. RMS
high intensity music personal safety acceleration
Note
Appendix 1, Section A1.5 deals with Root Mean Square (RMS) accelerations and how these are defined and used in analysis.
3
3 Listed Engineers
3.1 Requirement for specialist engineering expertise
Grandstands, and particularly the combination of a crowd of people and a grandstand,
provide technical and managerial problems that can be addressed satisfactorily only
by engineers with appropriate specialist expertise in addition to all round competence
underpinned by professional qualifications.
Whichever Route is chosen for design or assessment, it is important that these functions,
and the provision of advice on safe operation, are undertaken by an engineer having relevant
expertise in the structural design and safe operation of grandstands. At the request of
Government, the Institution of Structural Engineers is putting in place a scheme to provide
a list of engineers with specific experience in the design, assessment and safe operation of
grandstands for dynamic crowd loading. In these Recommendations, such engineers will be
referred to as Listed Engineers.
It is proposed that any Design Team dealing with new grandstands or significant
alteration to existing grandstands should include a Listed Engineer with particular
responsibility for overseeing those aspects of design concerned with dynamic crowd
behaviour. Similarly, a Listed Engineer should be employed in assessing existing stadia
and in overseeing the hand-over procedures of new and altered grandstands.
3.2 Technical support
Listed Engineers will be expected to have sufficient personal specialised knowledge and
expertise relating to the design and safe operation of grandstands to advise management
on all aspects connected with dynamic crowd loading. However, it would be expected that
Listed Engineers themselves may need to employ specialist support in respect of physical
testing and the conduct of dynamic structural analysis undertaken under their direction or
on their instruction.
3.3 Discretion on relevance of the Recommendations to specific structures
Grandstands vary in type, size and manner of use. Depending on the circumstances, detailed
consideration of crowd action may not be appropriate for a particular grandstand and,
based on their experience and technical background, Listed Engineers will be expected to
use their discretion in deciding the relevance of the Recommendations to such cases.
The Listed Engineer’s report to the grandstand’s Management should make clear
whether discretion has been exercised and the reason for doing so. It will be appreciated
that the management of a grandstand has responsibility for the safety of the facility
and so needs to understand and take responsibility for accepting the Listed Engineer’s
recommendations. The Listed Engineer’s report should also be made available to the Local
Authority concerned with Building Control and Safety Certification.
3.4 Judgment on relevance of the Recommendations to specific
structures
Listed Engineers will be expected to have the necessary background to use their own
judgment in interpreting and applying the Recommendations to particular grandstands.
The main areas for exercising judgment will normally be in advising the client
when choosing the appropriate Design Event Scenario, in detailed consideration of the
approximations involved in structural modelling and in assessing the need for structural
testing.
4 Dynamic performance requirements for permanent grandstands subject to crowd action
In making these judgments, the Listed Engineer should bear in mind that, in respect
of dynamic behaviour, the aim should be to remove the need to consider structural
behaviour from the wider risk assessment necessary for an event as a whole. If followed,
the Route 1 approach provides for this based on measured natural frequencies and the
frequency limits in Figure 1. (See Section 6.6). The Route 2 approach provides more
flexibility in decision making but depends on estimates of performance using calculations
based on recommended values for crowd loading that are considered typical for different
types of events. Sufficiently accurate values of natural frequency are required for both
approaches whilst a Route 2 analysis needs a more complete knowledge of dynamic
behaviour including a full set of relevant modal properties.
Because of the importance of accurate knowledge of dynamic properties, either
in characterising the admissible use of a grandstand using Route 1, or, as the basis of
design or assessment by Route 2, it will normally be considered necessary for the values of
dynamic properties to be established, or checked, using physical testing. (See Section 5 on
Testing). There will be circumstances where testing is not necessary, so placing a particular
responsibility on the Listed Engineer to exercise personal judgment on the need for physical
testing to check or establish values of dynamic properties. Such a judgment should not be
influenced by considerations of cost, convenience or time pressure but, solely, on a decision
that, in the particular circumstances being considered, the wider information available
from testing would not materially affect decisions on either design or assessment.
As in the use of discretion on the relevance of Recommendations to a particular
grandstand, the Listed Engineer’s report to the grandstand’s management should make
clear whether personal judgment has been exercised on any particular Recommendation,
including the need for testing, and the reason for doing so. The Listed Engineer’s report
should also be made available to the Local Authority concerned with Building Control and
Safety Certification.
3.5 Monitoring
The Listed Engineer should be involved with and advise on any programme to monitor the
behaviour of a stand whilst in use under crowd loading. Monitoring could include visual
recording of crowd behaviour, acceleration and load measurements, stewards’ reports etc.
Dynamic performance requirements for permanent grandstands subject to crowd action 5
