Dynamic comfort criteria for structures: A review of UK codes, standards and advisory documents

60 Pages·2011·2.265 MB·English

by  Gordon Breeze

DYNAMIC COMFORT CRITERIA FOR STRUCTURES
A review of UK codes, standards and advisory documents
The effects of vibration are becoming an increasingly important issue in the
DYNAMIC COMFORT CRITERIA
design of buildings and building elements. Modern construction methods
mean that buildings are becoming lighter and have less structural damping.
The response of such buildings to imposed vibration is therefore increased,
FOR STRUCTURES
so people using the buildings are more likely to experience vibration. Over a
number of years, different serviceability criteria have been developed to ensure
that buildings and building elements are suitable for their intended activity.
A review of UK codes, standards and advisory documents
This BRE Trust Report draws together the themes and disparate (sometimes
conflicting) acceleration comfort criteria associated with the vibration
of buildings in the UK. It reviews Eurocodes (including the UK National
Gordon Breeze
Annexes), British Standards, International (ISO) Standards and other sources
of information. The UK Building Regulations and advice provided by UK trade
associations and other industry bodies are also considered.
This report is technical in nature, and is aimed primarily at building designers,
consultants, architects and structural engineers. It is hoped that the complex
and interlinking nature of this subject can be understood by presenting all the
relevant acceleration criteria in one document in a logical and concise way.
z
y x
RELATED TITLES FROM IHS BRE PRESS
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FB 22, 2010
THE RESPONSE OF STRUCTURES TO DYNAMIC CROWD LOADS, 2004 EDITION
DG 426, 2004
WIND LOADS ON UNCLAD STRUCTURES
SD 5, 2004
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FB 33

DYNAMIC COMFORT CRITERIA
FOR STRUCTURES
A review of UK codes, standards and advisory documents
Gordon Breeze
ii
This work has been funded by BRE Trust. Any views The information and data presented in this report are up
expressed are not necessarily those of BRE Trust. While to date at the time of publication. Over time, values given
every effort is made to ensure the accuracy and quality of in standards and codes of practice change. Nevertheless,
information and guidance when it is first published, BRE the themes underpinning the methodologies described
Trust can take no responsibility for the subsequent use of are likely to remain the same for the foreseeable future.
this information, nor for any errors or omissions it may
contain. For the purpose of drawing comparisons and presenting
different approaches, information from many referenced
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• built facilities that offer improved functionality and practice.
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• a more efficient and sustainable construction sector,
with
• a higher level of innovative practice.
A further aim of BRE Trust is to stimulate debate on
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Printed on paper sourced from responsibly managed Cover images:
forests Main: BRE laser system used to measure pinnacle
vibration
FB 33 Top right: Grandstands at Everton Football Club (courtesy
© Copyright BRE 2011 of Everton Football Club)
First published 2011 Middle right: Geocentric coordinate axis system
ISBN 978-1-84806-173-6 Bottom right: A ‘grandstand’ rotary shaker used by BRE
CONTENTS iii
CONTENTS
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Executive summary � iv
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1 INTRODUCTION � 1
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2 BACKGROUND INFORMATION � 3
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2.1 Preamble 3

2.2 Units of acceleration 3

2.3 Coordinate axis systems 3

2.4 Acceleration vectors 4

2.5 Weighting factors 4

2.6 Measures of acceleration 5

3 GENERAL ACCELERATION CRITERIA � 7
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4 HORIZONTAL ACCELERATION CRITERIA � 9
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4.1 Preamble 9

4.2 Wind criteria 9

4.3 Criteria not related directly to wind 10

5 VERTICAL ACCELERATION CRITERIA � 18
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5.1 Preamble 18

5.2 Eurocodes 18

5.3 International (ISO) Standards 21

5.4 British Standards 22

6 SPECIALISED BUILDINGS � 24
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6.1 Grandstands and sports stadia 24

6.2 Hospitals 25

6.3 Car parks 27

7 � GUIDANCE GIVEN BY UK BUILDING REGULATIONS, TRADE ASSOCIATIONS 28
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AND OTHER INDUSTRY BODIES
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7.1 UK Building Regulations 28

7.2 Trade associations and other industry bodies 28

8 � DYNAMIC TESTING OF BUILDINGS AND BUILDING ELEMENTS 32
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8.1 Preamble 32

8.2 Introduction 32

8.3 Commonly used test methods 33

8.4 Practical use of dynamic testing 38

9 � CONCLUSIONS 40
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10 � REFERENCES 41
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Appendix A Vectors and vector addition 44
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Appendix B Buildings with complex vibration motions 46
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Appendix C Acceleration weighting factors 49
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iv EXECUTIVE SUMMARY
EXECUTIVE SUMMARY
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The effects of vibration are becoming an increasingly The present status of dynamic testing (both laboratory
important issue in the design of buildings and building and offsite) is also discussed, as well as the underlying
elements. Modern construction methods mean that principles of commonly used test methods. Information is
buildings are becoming lighter and have less structural provided about what can be measured and what can be
damping. The response of such buildings to imposed inferred from those measurements. This part of the report
vibration is therefore increased, so people using the gives practical advice, and full-scale measurements are
buildings are more likely to experience vibration. Over a presented that illustrate the issues raised.
number of years, different serviceability criteria have been This review is technical in nature, and is aimed
developed to ensure that buildings and building elements primarily at building designers, consultants, architects
are suitable for their intended activity. and structural engineers. It is hoped that the complex
The purpose of this BRE Trust Report is to distil and and interlinking nature of this subject can be understood
draw together the themes and disparate (sometimes by presenting all the relevant acceleration criteria in one
conflicting) acceleration comfort criteria associated with document in a logical and concise way.
the vibration of buildings in the UK. This report considers
the Eurocodes (including the UK National Annexes),
British Standards, International (ISO) Standards and other
sources of information. The UK Building Regulations
and advice provided by UK trade associations and other
industry bodies are also considered.
page header right – page1 h eiNatdreOr dsUuCbtt iiOtlNe 11
1 iNtrOdUCtiON
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The effects of vibration are becoming an increasingly important issue in the
design of buildings and building elements. Modern construction methods
mean that buildings are becoming lighter and have less structural damping.
The response of such buildings to imposed vibration is therefore increased,
so people using the buildings are more likely to experience vibration. If
the vibration is large enough it can cause annoyance, motion sickness and
ultimately panic. Over a number of years, different serviceability criteria have
been developed to ensure that buildings and building elements are suitable for
their intended activity.
Issues concerned with structural integrity (and hence safety) are not
considered in this report. When a properly designed structure is subjected
to vibration, people tend to become uncomfortable well before the limiting
state of the design is reached. Hence, the serviceability requirements tend to
be the critical factor in structures with human occupants. Although there are
serviceability criteria associated with the appearance of building finish and
public health, this report is limited to a consideration of the intrusive effect of
vibration upon people.
The aim of serviceability criteria is to ensure that a structure is suitable for
its intended use. Within the population there is a wide range of sensitivity
to vibration. Generally, children are the most sensitive to vibration and adult
males the least sensitive. Both the activity and posture of a person affect their
perception of vibration. A person’s expectation and exterior cues (such as
sound) are also important factors. This wide number of complicating factors
means that serviceability criteria can never be precise: what one person
judges to be a tolerable level of vibration may be perceived by another
to be annoying. Therefore, judgements often need to be made about the
percentage of the population that would perceive the vibration conditions to
be unacceptable; these judgements can have significant financial implications.
For this reason, many codes of practice recommend that agreement is
reached between the designer and the client beforehand about limiting
vibration threshold levels.
As noted above, vibration serviceability criteria have been developed
over many years. Some of these criteria have been developed for specific
applications, whereas others have more general application. Although there
are many similarities, there are also differences in the approaches used. Some
of the methods relate to specified return time periods (eg one-year, five-year
or 10-year periods), other methods relate to specific periods of vibration (eg
a 16-hour day or eight-hour night). There is uncertainty about how criteria
developed on the basis of simple vibration modes can be extended or
interpreted for cases where a structure vibrates in a more complex way. Some
methods give ranges of limiting accelerations, whereas other methods give a
specific value. Also, some approaches conflict with other methods, and no
two methods give consistent agreement with each other. There is not even
consistent agreement about the units of acceleration, although the units are
easily converted.
Many countries (eg the UK, the USA, Canada, Australia, New Zealand, The
Netherlands, Japan, France, Germany and Denmark) have their own national
22 pdaYgNea MheiCa dCOerM flOefrt t –Cr pitaegrei ah efaOdre rS tsruUbCttit Uler eS
codes of practice and standards, within which are contained building-related
serviceability criteria. It is not the purpose of this report to compare and
contrast the criteria adopted by each country. Instead, this study focuses on
identifying and reviewing information that is relevant to buildings in the UK.
Nevertheless, where appropriate, attention is drawn and references made to
sources of information from other countries.
The UK falls under the scope of the following codes of practice and
standards: the Building Regulations 2000 (England and Wales)[1], Eurocodes
(including the UK National Annexes), International (ISO) Standards and British
Standards. There are also documents giving advice about specific building
applications; these specialised approaches tend not to be consistent with other
sources. The issue as to which standards and documents have precedence
over others is touched upon in this review. However, a resolution of this matter
is outside the scope of this report.
The aims of this review are:
1. To bring together state-of-the-art knowledge about vibration comfort
criteria that are appropriate for three building-related areas in the UK
where vibration has proved to be an important recurring issue, namely
buildings, floors and grandstand risers.
2. To discuss dynamic test methods presently used.
page header r2ig BhatC –Kg praOgUeN hde aiNdfeOrr sMuabtt iiOtlNe 33
2 BaCKgrOUNd iNfOrMatiON
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2.1 preaMBle
In the literature, it is generally accepted that people’s perception of vibration
is related to the rate of change of acceleration (or ‘jerk’). However, with one
exception all of the vibration comfort criteria found in the literature are related
to acceleration. The continuance of this approach results from the fact that
acceleration levels can be measured relatively easily. This means that both the
measurement and interpretation of accelerations have been undertaken for
many years. Consequently, practising engineers have become familiar with this
method over time, and are therefore reluctant to change.
2.2 UNitS Of aCCeleratiON
As noted earlier, the units of acceleration differ in many of the assessment
methods used; the units include m/s2, cm/s2, mm/s2, %g and milli-g (note that
g is acceleration due to gravity, usually taken as 9.81 m/s2). The International
System of Units (SI) unit of acceleration is m/s2, and this unit will be used
throughout this review. Where appropriate, units presented in other formats
will be converted into m/s2.
2.3 COOrdiNate axiS SYSteMS
Before proceeding, orthogonal axes need to be defined that can be used
to reference specific directions in three-dimensional space. This is because
acceleration is a vector quantity, and has both magnitude and direction.
Considering first the commonly used basicentric coordinate axis system, the
z-axis is the foot-to-head direction, the x-axis is the front-to-back direction
and the y-axis is the side-to-side direction. This coordinate system is shown in
Figure 1 for a person standing, sitting and lying down.
x
z
z y z
y
Lying down
Figure 1: Basicentric coordinate axis system
x
y
x
Sitting
Standing
44 pdaYgNea MheiCa dCOerM flOefrt t –Cr pitaegrei ah efaOdre rS tsruUbCttit Uler eS
Although the basicentric axis system relates to a human body whatever the
activity, the latest trend[2] is a movement towards the use of the geocentric
coordinate axis system. This system relates to the building geometry instead
of the body. In this situation, the z-axis is vertical and the x- and y-axes are in
horizontal (or lateral) directions. Figure 2 illustrates the geocentric coordinate
axis system.
z
y x
Figure 2: Geocentric coordinate axis
system
(Note that the x- and y-axes are
abritrary, but are usually chosen to align
with the major building axes)
2.4 aCCeleratiON veCtOrS
As noted in the previous section, accelerations are vectors. When two or more
accelerations occur at the same time in different directions, their simultaneous
effect consists of the vector sum of all of the accelerations. The method by
which a vector sum can be calculated is described in Appendix A.
Whichever orthogonal axis system is used, the magnitude (or amplitude) of
the time-varying acceleration, a(t), is defined by Equation 1:
(Equation 1)
where a(t), a(t) and a(t) are the time-varying accelerations in the x-, y- and
x y z
z-axis directions, respectively.
In many applications (such as the vertical vibration of floors), the principal
direction of the vibration is obvious. However, when considering the
dynamic motion of a building that twists and bends, the combined effect of
the accelerations in the two orthogonal lateral x- and y- directions (which
incorporates the effect of torsion) needs to be considered. Unless it is explicitly
stated otherwise, it will be assumed that the magnitude of acceleration, a(t), is
used as the basis for the vibration comfort criteria.
2.5 WeightiNg faCtOrS
To take into account human perception of vibration, many (but not all)
methods apply weighting factors to measured acceleration signals. The
weighting factors are different depending upon the orientation of the body,
and this reflects the fact that people are generally most sensitive to vibration
when standing (as opposed to sitting or lying down). When required, the
appropriate weighting factors are specified in the methodology used.
Weighting can be applied in either the time or frequency domains, and
weighted accelerations will henceforth be denoted by the subscript . Hence,
w
the time-varying weighted magnitude of acceleration is denoted by a (t).
w
Section 4 presents base-line curves that show the threshold of acceleration
perception, ie the vibration level at which motion is felt. These curves are