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Disclosure to Promote the Right To Information
Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.
इंटरनेट मानक
“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda
“Invent a New India Using Knowledge”
“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru
“Step Out From the Old to the New”
“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan
“The Right to Information, The Right to Live”
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”
“Invent a New India Using Knowledge”
है”ह”ह
IS 14884 (2000): Mechanical Vibration and Shock - Vibrationof Buildings - Guidelines for the Measurement of Vibrationsand Evaluation of Their Effects on Buildings [MED 28:Mechanical Engineering]
IS 14884 : 2000 ISO 4866 : 1990 (Reaffirmed 2010)
Indian Standard MECHANICAL VIBRATION AND SHOCK — VIBRATION OF BUILDINGS — GUIDELINES FOR THE MEASUREMENT OF VIBRATIONS AND EVALUATION OF THEIR EFFECTS
ON BUILDINGS
ICS 17.160
© BIS 2000
BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
October 2000 Price Group 10
Mechanical Vibration and Shock Sectional Committee, ME 28
NATIONAL FOREWORD
This Indian Standard which is identical with ISO 4866 : 1990 'Mechanical vibration and shock — Vibration of buildings — Guidelines for the measurement of vibrations and evaluation of their effects on buildings' issued by the International Organization for Standardization (ISO) was adopted by the Bureau of Indian Standards on the recommendations of the Mechanical Vibration and Shock Sectional Committee and approval of the Mechanical Engineering Division Council.
The text of ISO standard has been approved as suitable for publication as Indian Standard without deviations. In the adopted standard, certain conventions are, however, not identical to those used in Indian Standards. Attention is especially drawn to the following:
a) Wherever the words 'International Standard' appear referring to this standard, they should be read as 'Indian Standard'.
b) Comma (,) has been used as a decimal marker while in Indian Standards, the current practice is to use a full point (.) as the decimal marker.
Amendment 1 to the above International Standard has been printed at the end.
In this adopted standard, reference appears to certain International Standards for which Indian Standards also exist. The corresponding Indian Standards which are to be substituted in their place are listed below along with their degree of equivalence for the editions indicated:
International Standard Corresponding Indian Standard Degree of Equivalence
ISO 2041 : 1990 IS 11717 : 2000 Vocabulary on vibration Identical and shock (first revision)
ISO 2631 2 : 1989 IS 13276 (Part 2) : 1992 Evaluation of do human exposure to whole body vibrations: Part 2 Continuous and shock induced vibrations in buildings (180 Hz)
ISO 5348 : 1987 IS 14883 : 2000 Mechanical vibration and do shock: Mechanical mounting of accelerometers
The concerned technical committee has reviewed the provisions of the following International Standards referred in this adopted standard and has decided that they are acceptable for use in conjunction with this standard:
International Title Standard
ISO 4356 : 1977 Bases for the design of structures Deformations of buildings at the serviceability limit states
IEC 68227 : 1987 Environmental testing Part 2 : Tests Test Ea and Guidance : Shock
For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960 'Rules for rounding off numerical values (revised)'. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.
Amend No. 2 to IS 14884 : 2000
AMENDMENT NO. 2 AUGUST 2007 TO
IS 14884 : 2000/ISO 4866 : 1990 MECHANICAL VIBRATION AND SHOCK — VIBRATION OF BUILDINGS — GUIDELINES FOR THE MEASUREMENTS OF
VIBRATIONS AND EVALUATION OF THEIR EFFECTS ON BUILDINGS
[Page 17, Annex D (see also Amendment No. 1)] — Insert the following Annex as Annex E and renumber the existing Annex E as Annex F:
Price Group 4 1
Amend No. 2 to IS 14884 : 2000
Annex E (informative)
Vibrational interaction between the foundation of a structure and the soil
E.1 General
When vibration measurements cannot be made on the foundation of a structure or inside a building, ISO 4866 allows that measurements be made on the ground surface outside. It may also be necessary to predict the response of a building not yet constructed. In both cases there is a need to understand the dynamic interaction between a building and the ground.
In the first case, the most suitable position outside the building for measurement and the relationship between the signal at that position and that on the building foundation need to be established.
In the second case, the response of the foundation of the building may be expected to follow closely the motion of the ground in contact with the foundation unless interaction is significant. This annex seeks to indicate the nature of such an interaction and suggests procedures which allow it to be taken into account.
Figure E.1 illustrates the notation which will be used in this annex in terms of the peak amplitude, u, of a travelling wave passing across a foundation (u can be the displacement, velocity or acceleration amplitude of the sinusoidal wave). Freefield amplitude is denoted by uo, amplitude in the base of the foundation by up, amplitude at an arbitrary position in the structure by ust, and on the soil surface near an existing building by u^. Far from the structure, uN = u0. Soilstructure interaction analysis is concerned generally with the relationship between freefield motion and structure motion, that is ust/u0 and, in particular, uF/u0 = r0. The important ratio uf/u^ = rN is given by the more sophisticated procedures which also address the problem of soil response involving the variation of vibration amplitude with depth.
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Amend No. 2 to IS 14884 : 2000
Symbols:
µ is the displacement, velocity or acceleration amplitude of the sinusoidal wave;
µ0 is the freefield amplitude; µN is the amplitude on the soil surface near an existing building;
µF is the amplitude in the base of the foundation;
µst is the amplitude at an arbitrary position in the structure.
r0 = µF/µ0 rN = µF/µN
Figure E.1 — Notat ions , illustrated at a horizontally propagating w a v e
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Amend No. 2 to IS 14884 : 2000
E.2 Theoretical considerations
Soilstructure interaction influences the dynamic response of all structures to some degree. Only a rigid building bonded to rigid ground would respond in the same way as the ground. In reality, the ground does not have an infinite rigidity and may provide a mechanism for the radiation and dissipation of energy. Hence it can be thought of as acting as a spring and dashpot system or a series of such systems just below the foundation.
The degree to which soilstructure interaction is a significant aspect of structural response depends on the dynamic parameters of the structure and of the ground, in particular on the natural frequencies of the structure and the shear stiffness of the ground. When considering relatively stiff lowrise buildings (low rise = 6 m to 7 m high), the problem may be examined as the vertical response of a rigid mass on a spring and a dashpot adjusted to match the analytical solution with the ground as semiinfinite isotropic and homogeneous elastic halfspace. Such simple concepts suggest that the maximum amplification to be expected in the vertical direction is not likely to exceed 2. Rocking and sliding modes can also be explored in a similar manner and suggest that somewhat higher magnifications can be theoretically achieved in most cases. However, vertical amplification is surely limited because energy captured by the structure from the passing wave is reradiated into the ground thus damping the amplitude response.
Full consideration of soilstructure interaction should take account of the layering of the soil, the variation of shear stiffness with depth, the effects of building load on soil stiffness, the effect of shear strains on soil stiffness, the geometry of the foundation, and foundation embedment, as well as the frequency content of the excitation.
Dynamic soilstructure interaction is one of the central problems in earthquake engineering, and over the last two decades methods of analysis have been highly developed, mainly for the nuclear industry, giving rise to a vast literature (see references [39] to [45]). Refined analysis has also been used for wind and manmade loading and some simplified rules have been derived (see references [46] and [47]).'
These advanced analytical methods can be grouped into two classes:
a) the direct method, whereby the soil and structure are treated together; the ground may be represented by finite elements, lumped parameters or both (hybrid models);
b) the substructure method, whereby the response of the ground and structure are calculated as separate systems with a separation between ground and structure to which springs and dashpots or stiffness functions are applied.
Another approach is the response spectrum, widely used in earthquake engineering and other shock loading (see reference [48]). It can be adapted to take some account of soilstructure interaction by reducing the natural frequency assessed for a structure on soils of low stiffness. The effects of soil response can be allowed for, in part, by using design response spectra which vary according to the shear modulus depth profile of the soil.
Generally, the closer the frequency of the excitation is to the natural frequency of a building or building element the greater will be the response. Earthquakes, with low frequencies of 0,5 Hz to 8 Hz, will tend to excite the lower natural frequencies of buildings; manmade excitation is generally at higher frequencies and tends to excite the structural elements of a building. Furthermore, the range of vertical frequencies of building elements (6 Hz to 40 Hz) lies in the range of manmade excitation, leading to the relatively large bending responses which have been observed in ceilings (see reference [49]).
E.3 Relationship between vibration at the ground surface and at the foundation
There are difficulties associated with measurements on the ground near the building, for example:
— the measuring point is usually remote from the positions of interest within the structure;
— there are more uncertainties in coupling the transducer to the ground than in fixing it to a building part;
— the soil near a building is often disturbed;
— vibration amplitudes near a building may change with distance from the building as a proportion of the wavelength.
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Around No. 2 to IS 14884 : 2000
The direct methods for analysis of soilstructure interaction are expensive and need detailed knowledge of soil properties, however, they can give some guidance on the following factors influencing rN.
a) The amplitude of vibration may be affected by reflection at the front of the foundation (with respect to the travelling wave) and decreased at the rear side by dissipation and front side reflection. Theses effects depend on the foundation size, depth and excitation wavelength.
b) Where the propagation behaves like a surface Rayleigh wave (which is usual for distant sources), the amplitudes decrease with depth (see, for example, figure E.2), so deeper foundations pick up less motion.
c) Strong earthquake motions are usually modelled as vertically propagating horizontally polarized shear waves with amplitudes increasing as the waves pass upwards from high rigidity. So again, deeper foundations may pick up smaller vibration.
Such complexities preclude a definitive set of rules relating rN and r0 to the category of structure and character of excitation, but both measurements (see reference [50]) and theoretical studies indicate that in most situations of manmade excitations the value of rN is likely to be unity or less. This has been supported by results of a questionnaire1) which has indicated that for vertical motion without regard to frequency, rN was in the range 0,3 to 0,6. The maximum magnification recorded was in the horizontal response and amounted to a 13 % increase. Histograms of the replies to the questionnaire are given in figures E.3 and E.4.
This general reduction of vertical vibration on the foundation as compared with that on the soil surface near a building may not hold in cases where there is a marked rocking response to continuous vibration.
As for preferred positions of measurement near a building, it is suggested that these positions should be less than 2 m or 1/10 of the dominant wavelength away from the building.
1) The questionnaire contained various ground conditions as well as various types of vibration excitation.
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Amend No. 2 to IS 14884 : 2000
??? is the Rayleigh wavelength.
Figure E.2 — Variation of vibrational amplitude µZ with depth z of a Rayleigh wave
Amend No. 2 to IS 14884 : 2000
Figure E.3 — Frequency distribution of rN (vertical direction of vibration)
Figure E.4 — Frequency distribution of rN (horizontal direction of vibration)
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Amend No. 2 to IS 14884 : 2000
Page 18
Add references [39] to [50] to annex F.
[39] NEWMARK, M. and ROSENBLUTH, E. Fundamentals of earthquake engineering. Prentice Hall, 1973.
[40] RICHARD, F.E., HALL, J.R. and WOODS. R.D. Vibrations of soils and foundations. Englewood Cliffs, NJ, 1970.
[41] WOLF, J.P. Dynamic soil structure interaction. Prentice Hall, 1985.
[42] CLOUGH, R.W. and PENZIEN, J. Dynamics of structures. McGraw Hill Corp., New York, 1975.
[43] WARBURTON, G.B., RICHARDSON, I.D. and WEBSTER, J.J. Forced vibrations of two masses on an elastic halfspace. Transactions ASMS, March 1971.
[44] HOLZLOHNER, U. Dynamically loaded buildings on the soil. Proc. XICSMFE, Vol. 3, Stockholm, 1981.
[45] ROESSET, J.M. and GONZALES, J.J. Dynamic interaction between adjacent structures. Proc. DMSR, Karlsruhe 1977, Vol. 1, Balkema, Rotterdam, 1978.
[46] ELLIS, B.R. Dynamic soil structure interaction in tall buildings. Ph.D. Thesis, University of London, 1984.
[47] AUERSCH, L. Durch Bodenerschutterungen angeregte Gebaudeschwingungen — Ergebnisse von Modellrechnungen. BAM Research Report 108, Wirtschaftsverlag NW, Bremerhaven, 1984.
[48] FOSTER, G.A. Structural response and human response to blasting vibration effects — is there a connection? Vibratech report, 1985.
[49] AUERSCH, L., HEBENER, H. and RUCKER, W. Erschütterungen infolge Schienenverkehr: Theoretische und meβtechnische Untersuchungen zur Emission, zur Ausbreitung durch den Boden und zur Ubertragung im Gebäude. STUVA Report No. 19 (series Verminderung des Verkehrslärms in Städten und Gemeinden, Teilprogramm Schienennahverkehr), 1986.
[50] SISKIND, D.E. and STAGG, M.S. Blast vibration measurements near and on structure foundations. Report of Investigations R1 8969, US Bureau of Mines, 1985.
(MED 28)
Reprography Unit BIS, New Delhi, India
IS 14884 : 2000 ISO 4866 : 1990
AMENDMENT 1
Page 17
Add the following annex as annex D and change the present annex D to annex E.
Page 18
Add references [24] to [38] to annex E.
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IS 14884 : 2000 ISO 4866 : 1990
Annex D (informative)
Predicting natural frequencies and damping of buildings
Introduction
ISO 4866:1990 specifies methods of measuring building response including fundamental natural frequencies. When direct measurements cannot be made or are limited in usefulness by high damping, subcomponent resonances or other practical problems, it becomes necessary to estimate natural frequency and damping values.
This annex offers guidance on the ways in which the fundamental natural frequency and associated damping value may be assessed. It draws attention to the uncertainties involved which should be taken into account wherever an estimation of fundamental natural frequencies of a building is used in measuring or evaluation procedures.
D.1 Predicting natural frequencies of tall buildings using empirical methods
There are many empirical formulae for predicting the frequency f, or period T, of the fundamental translation mode; of these the simplest is f = 10/N Hz (i.e. T = 0.1 N s). where N is the number of storeys. Various other formulae are given in the codes of different countries and these can be grouped into three categories:
T = k1 H
where
H is the height, in metres;
T is the period, in seconds;
k1 ranges from 0,14 sm1 to 0,03 sm1
(references [24] to [271]).
...D.1
T = k2H√ D . . . D.2
where
D is the width parallel to the force, in metres;
k2 ranges from 0,087 sm3/2 to 0,109 sm3/2
(references [25] and [28]).
T = k3 H √ D func(H,D,I) . . . D.3
(see, for example, reference [29]).
NOTE 1 k1 has the units sm1; k2 has the units sm3/2.
A later study [301, considering a sample of 163 rectangularplan buildings, recommended f = 46/H Hz∙m (i.e. T = 0,022// sm1) for the fundamental translation mode, f = 58/H Hz∙m for the orthogonal fundamental translation mode and f = 72/H Hz.m for the fundamental torsional mode (sample size of 63 buildings).
NOTE 2 These formulae for f are empirical. They may also be considered as numerical value equations yielding values of f in hertz when values of H in metres are inserted, for instance f = 46/H.
Figure D.1 shows the resulting fit of the curve f = 46/H Hz∙m to the data and it can be appreciated that large errors are likely to be encountered. It can be seen that errors of ± 50 % are not uncommon, and this is typical of the accuracy which can be expected using empirical formulae. Based on measured data, it appears that the mode shapes of the fundamental modes of tall buildings can be reasonably approximated by straight lines.
20
IS 14884 : 2000 ISO 4866 : 1900
D.2 Predicting natural frequencies of tall buildings using computer-based methods
properties of buildings. Predictions of fundamental frequencies should therefore be treated with caution.
It has long been realised that comparatively large errors are likely to occur using the simple empirical formulae, but it has also been generally accepted that a satisfactory estimate of frequency can be obtained using one of the standard computerbased methods. However, buildings are complicated structures and it is not a simple task to create an accurate mathematical model; consequently it must be accepted that these models will only provide approximate predictions. In a study [30] examining published evidence, the correlation between computed frequencies and measured frequencies was actually considerably worse than the correlation between the frequencies predicted using f = 46/H Hz∙m and the measured values. This discrepancy can be attributed to inadequacies in modelling the real
Special methods have been developed for analysis of core buildings [31], shear buildings [32] and sway frame and frame buildings [33], but with any method it is important to check whether the method has been calibrated using a range of reliable experimental data and to understand what errors are likely to be encountered. If the method has not been proven, then accuracies greater than those obtained for empirical predictors should not be assumed. Only the fundamental frequencies have been discussed, but the predicted frequencies of higher frequency modes will suffer from similar or (more probably) greater errors. This means that, except for special cases where the mathematical model has been tuned to experimental results, predictions involving many calculated modes must be regarded as unreliable.
Figure D.1 — Plot of height versus fundamental frequency for 163 rectangular-plan buildings using logarithmic scales
21
IS 14884 : 2000 ISO 4866 : 1990
D.3 Predicting damping values of tall buildings
The damping (or rate of energy dissipation) in any one mode limits the motion in that mode, and consequently to estimate the building response to a given load it is necessary to estimate or measure the amount of damping. No proven methods of predicting damping exist and the measured data show that damping values between 0,5 % and 2,1 % critical can occur (see figure D.2). Higher values may also be encountered in buildings where soil/structure inter
action is significant. Simple steel frames are likely to have much lower damping. Methods of predicting damping have been developed (see refs. [34] and [35]) but, again, the expected accuracy is not quoted.
Figure D.2 shows a plot of damping versus building height for a selected sample of buildings [36]. It can be seen that large differences in damping can be obtained for orthogonal translation modes of the same building. Damping is partly a function of the construction procedures and workmanship involved and cannot be predicted accurately. Consequently, large errors in estimation must be anticipated.
Domping ratio, % critical
Figure D.2 — Building height versus damping ratio for the fundamental translation modes of 10 buildings where soil/structure interaction was negligible (from decay measurement)
22
IS 14884 : 2000 ISO 4866 : 1990
D.4 Natural frequencies and damping values in low-rise buildings
The characteristics of 96 lowrise buildings are presented in references [37] and [38]. The buildings were located in the USA and are described as 1, 1½ and 2 storey buildings with basements, partial basements or crawl spaces. The data show that the average measured frequency decreases with building height.
Figure D.3 shows a histogram relating the number of buildings to their measured frequencies. It is important to note the range of frequencies which is encountered and thus the error involved in using an empirical prediction. There is no obvious tendency for the frequencies to vary with the age or location of the houses, and there is no correlation of the frequencies with plan dimensions.
Figure D.4 shows a histogram relating the number of buildings to their damping ratios. This indicates generally higher damping ratios than for taller buildings and shows the range of damping values which may be encountered. No obvious relationship between damping and building geometry exists.
D.5 Non-linear behaviour The previous clauses discuss the natural frequency and the damping of each mode and this might give the impression that these quantities are invariant. However, they do vary with amplitude of motion and for earthquake analyses this might be important (albeit difficult to quantify). In general, wind loading induces small amplitude motion (in comparison with large earthquakes) and the changes in natural frequency and damping over the range of amplitudes normally encountered is small. In one building which was subjected to forces equivalent to a range of winds from light to hurricane force, changes of 3 % in frequency and 30 % in damping were recorded [36]. It can be appreciated that these changes are perhaps not significant and can be ignored for design purposes.
D.6 Final comment The general conclusion which can be reached from this annex is that theoretical predictions are likely to involve considerable inaccuracies. Consequently, theoretical analyses should consider these possible inaccuracies by carrying out parametric variation and, for important structures, the design calculations should be verified using experimental measurements when the structure is complete.
23
Figure D.3 — Frequencies measured in 96 low-rise buildings
IS 14884 : 2000 ISO 4866 : 1990
Figure D.4 — Damping ratios measured in 96 low-rise buildings
24
IS 14884 : 2000 ISO 4866 : 1990
Bibliography
[24] KAWECKI, J. Empirical formulae used for calculating the natural periods of vibrations of buildings. Czasopismo Techniczne, Z 7-B (129), 1969.
[25] STEFFENS, R.J. Structural vibration and damage. Building Research Establishment Report, UK, 1974.
[26] BARKADZE, E.I. Problems of determining the results of instrumental measurements of natural periods of buildings. Soobs AN Groz, 39 (6), 1962.
[27] NAKA, T. Structural design of tall buildings in Japan. ASCEIABSE Joint Committee Report: Planning and design of tall buildings, Proc. 3rd Regional Conference, Tokyo, Sept. 1971.
[28] ANDERSON, A.W. et al. Lateral forces of earthquake and wind. Proc. ASCE, 77 (Separate) No. 66, 1951.
[29] Recommendations Association Française du Génie Parasismique 90. Presse des Ponts et Chaussées, Paris.
[30] ELLIS, B.R. An assessment of the accuracy of predicting the fundamental natural frequencies of buildings and the implications concerning the dynamic analysis of structures. Proc. Inst. Civ. Eng., 69, Sept. 1980.
[31] ESDU 81036, Undamped natural frequencies of core buildings. ESDU, London, Nov. 1981.
[32] ESDU 79005, Undamped natural vibration of shear buildings. ESDU, London, May 1979.
[33] ESDU 82019, Undamped natural vibrations of sway frame buildings and frame structures. ESDU, London, Aug. 1982.
[34] ESDU 83009, Damping of structures — Part 1: Tall buildings. ESDU, London, May 1983.
[35] JEARY, A.P. Damping in tall buildings — A mechanism and a predictor. Earthquake Engineering and Structural Design, 14, 1986.
[36] ELLIS, B.R. Dynamic soilstructure interaction in tall buildings. Ph.D. Thesis, University of London, 1984.
[37] MEDEARIS, K. The development of rational damage criteria for lowrise structure subjected to blasting vibrations. Report to National Crushed Stone Association, Washington DC, Aug. 1976.
[38] SISKIND, D.E. et al. Structural response and damage produced by ground vibration from surface mine blasting. US Dept. of Interior, Bureau of Mines, Rl 8507, 1980.
25
IS 14884 : 2000 ISO 4866 : 1990
Indian Standard MECHANICAL VIBRATION AND SHOCK — VIBRATION OF BUILDINGS — GUIDELINES FOR THE MEASUREMENT OF VIBRATIONS AND EVALUATION OF THEIR EFFECTS
ON BUILDINGS
1 Scope
This In te rna t iona l S t a nd a r d e s t a b l i s h e s the bas i c p r inc ip les for ca r ry ing out vibrat ion m e a s u r em e n t and p r o c e s s i n g da t a , with r e g a r d to eva lua t ing vibra t ion effects on bui ld ings . It d o e s not cove r the s o u r c e of exci ta t ion excep t insofar as the s o u r c e d i c t a t e s dynam i c r a ng e , f requency o r o t h e r p a r am e t e r s . The eva lua t ion of the effects of building vibra t ion is pr imari ly d i r e c t ed a t s t ruc tu ra l r e s p o n s e , and i nc ludes a pp r op r i a t e analy t ica l m e t h o d s wh e r e the f requency , dura t ion and amp l i t ude can be de fined This In te rna t iona l S t a nd a r d only d e a l s with the m e a s u r em e n t of s t ruc tu ra l v ibrat ion and e x c l ud e s the m e a s u r e m e n t o f a i r bo rne s ound p r e s s u r e and o t h e r p r e s s u r e f luctuat ions a l though r e s p o n s e t o such exc i t a t ions i s t aken into con s i de r a t i on .
A building, for the p u r p o s e s of this In te rna t ional S t a nda r d , i s def ined as any a bove g r ound s t ruc tu re , which man frequent ly inhab i t s This e x c l ud e s from cons i de r a t i on cer ta in i t ems of plant , for e x amp l e c o l umn s , s t a ck s , h e ad f r ame , c on t a i nmen t s , even t hough they may r e ce i ve in termi t ten t visits from op e ra t ing staff.
The s t ruc tura l r e s p o n s e of bui ld ings d e p e n d s upon the exci ta t ion; to this end this In te rna t iona l S t a nd a r d e x am i n e s t he m e t h o d s o f m e a s u r em e n t s a s affected by the s o u r c e , i.e. f requency , dura t ion , and ampl i t u d e s a s i nduced by any s ou r c e , s uch a s e a r t h q u a k e s , e xp l o s i on s , wind effects, son ic b o oms , in terna l mach i n e r y , traffic, cons t ruc t i on act ivi t ies and o t h e r s .
NOTE 1 There are differences between ear thquakes and manmade vibrations which affect recording conditions. Earthquakefaultrupture sources are large in size and much deeper than most manmade sources. They can cause damage at great distances, have much greater energy flux and duration and a different pattern of wave propagation. Consequently, for the same parameter value (for example peak particle velocity), the effects on buildings are different.
2 Normative references
The following s t a n d a r d s conta in p rov i s ions which, th rough r e f e r ence in this text, cons t i tu te p rov is ions of this In te rna t ional S t anda rd . At the t ime of publica t ion, the ed i t ions ind ica ted w e r e valid. All s tand a r d s a r e sub jec t to revis ion , and pa r l i e s to a g r e em e n t s b a s e d on this In te rna t ional S t anda rd a r e e n c o u r a g e d to i nves t iga t e t he possibil i ty of ap plying the mos t r e cen t ed i t ions of the s t a n d a r d s ind ica ted below. Memb e r s of IEC and ISO mainta in r eg i s t e r s of cur ren t ly valid In terna t iona l S t a n d a r d s
ISO 2041 1975, Vibration and shock — Vocabulary
ISO 26312:1989, Evaluation of human exposure to wholebody vibration — Part 2 Continuous and shockinduced vibrations in buildings (1 to 80 Hz).
ISO 4356 1977, Bases for the design of structures — Deformations of buildings at the serviceability limit states
ISO 5348:1987, Mechanical vibration and shock — Mechanical mounting of accelerometers.
IEC 68227:1987, Environmental testing Tests — Test Ea and Guidance: Shock.
– Part 2
3 Source-related factors to be considered
3.1 Characteristics of vibration responses in buildings
The t ype s of vibrat ion can be classif ied as
a) de t e rmin i s t i c ,
b) r a ndom ,
and further subd iv ided as g iven in 8.2
1
IS 14884 : 2000 ISO 4866 : 1990
For each type of vibration, a minimum amount of information is needed so that adequate definition of the type of vibration can be drawn up (see ISO 2041). [1]
3.2 Dura t i on
The dura t ion of the d yn am i c exci t ing force is an impor tant p a r ame t e r . For t he p u r p o s e s of this In ternational S t anda rd , t he r e s p o n s e can b e r e g a r d e d a s con t inuous o r t r ans i en t , and t he type o f r e s p o n s e will be d ic ta ted by t he r e l a t i onsh ip b e twe en the t ime con s t an t s a s s o c i a t e d with t h e s t ruc tu ra l r e s p o n s e and the forcing function.
The t ime cons t an t of a r e s o n a n c e r e s p o n s e for r e s o n an c e , r, in s e c o n d s , τr, is g iven by
whe r e
ξ r r e p r e s e n t s the inf luence of the d amp i ng and d e p e n d s on the kind of exci ta t ion (line a r o r non l inear ) ;
f r is the r e s o n a n c e f requency .
Two c a s e s can t hus be defined (without r e g a r d to whe t h e r or not the exci ta t ion is de t e rmin i s t i c or r andom) :
— Continuous
If the forcing function imp inge s on the s t ruc tu r e con t inuous ly for mo r e than 5τr , then the vibrat ion i s r e g a r d ed as con t i nuous .
— Transient
If the forcing function ex is t s for a t ime which is l e s s than 5τ r , then the r e s p o n s e i s r e g a r d e d as t r ans i en t .
S ince forcing functions which occu r natural ly a r e often not well b e h a v e d i t may be that r e s p o n s e s do not fall eas i ly into a s ing le ca t ego ry . For e x amp l e b las t ing even with s e v e r a l in te rva l s would be cons i de r ed t r ans i en t .
3.3 Frequency and range of vibration Intensity
The frequency range of vibrations of interest depends upon the distribution of spectral content over the frequency range of the excitation and upon the mechanical response of the building. This pinpoints the spectral content as a most important property of vibration input. For simplicity's sake, this International Standard deals with frequencies ranging from 0,1 Hz to 500 Hz; it covers the response of buildings of a wide variety and building elements to excitation
from natural (wind and earthquake) and to manmade (construction, blasting, traffic) causes . Internal machinery may require higher frequencies to be recorded.
Most building damage from manmade sources occurs in the frequency range from 1 Hz to 150 Hz. Natural sources, such as earthquakes, usually contain energy at lower frequencies in the range from 0,1 Hz to 30 Hz at damaging intensities. Wind excitation tends to have significant energy in the frequency range from 0,1 Hz to 2 Hz.
Vibration levels of interest range from a few to several hundred millimetres per second depending on frequency.
4 Buildingrelated factors to be considered
The reaction of buildings and building components to dynamic excitation depends upon response characteristics (for example natural frequencies, mode shapes and modal damping) as well as the spectral content of the excitation. Cumulative effects should be considered, especially at high response level and long exposure times where fatigue damage is a possibility.
4.1 Type and condition of buildings
In order to describe properly and categorize the visible effects of vibration and the results of Instrumental measurements, a classification of buildings as defined in clause 1 is needed. For the purposes of this International Standard, a classification of buildings is set out in annex A.
4.2 Natural frequencies and damping
The fundamental natural frequencies of a building or of parts of the building influence its response and need to be known to allow the several methods of evaluating vibration to be applied. This may be achieved by spectral analysis of lowlevel response to ambient excitation or by the use of exciters. [2]
Where a full response analysis is not undertaken and an assessment of potential vibration severity is needed, empirical expressions relating the height of a building to the fundamental period can be used. (3), [4] , [5]
Experimental studies[6] have indicated the range of fundamental shear frequency of lowrise buildings 3 m to 12 m high to be from 4 Hz to 15 Hz. Damping behaviour is generally amplitudedependent. The natural frequency and damping behaviour of stationary structures will be dealt with in a future addendum to this International Standard.
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4 .3 B u i l d i n g b a s e d i m e n s i o n s
Ground bo r n e v ib ra t ions may h a v e wav e l e n g t h s o f a few m e t r e s to s e v e r a l h u n d r e d s of me t r e s . The r e s p o n s e exc i ta t ion from sho r t e r wav e l e ng t h s i s c omp l ex and the founda t ions may act as a filter. Sma l l e r d ome s t i c bui ld ings would gene ra l l y h ave b a s e d imen s i o n s sma l l e r t han the cha r ac t e r i s t i c wav e l e n g t h s of all but the h ighes t f r equency s o u r c e s (for e x amp l e p rec i s ion b las t ing in rock).
4.4 I n f l u e n c e of so i l
It is now c ommon in e a r t h q u a k e eng i nee r i ng s t ud i e s to t ake into a ccoun t the inf luence of the soil. [ 3 ]
An eva lua t ion of such in terac t ion effects is s om e t imes justified for m a n m a d e v ibra t ions ; such an eva lua t ion d em a n d s that the s h e a r wave velocity o r dynami c rigidity modu l u s in an app rop r i a t e vo l ume of g round mate r i a l be d e t e rm i n ed . Empir ica l , numer ica l and analyt ical p r o c e d u r e s may be ob t a i n ed from s eve r a l s o u r c e s . [ 7 ]
Founda t i ons on poor soi ls and fill may suffer from s e t t l emen t or loss of bea r i ng capac i ty d u e to g round vibrat ion. The risk of s uch effects is a function of t he par t ic le s i ze of the soil, its uniformity, compac t ion1 ) , d e g r e e of s a tu ra t ion , in ternal s t r e s s s t a t e , as well as the p eak mult iaxial a c ce l e r a t i on and dura t ion of t he g round vibrat ion. Loose , c o h e s i o n l e s s , s a t u r a t e d s a n d s a r e e spec i a l l y vu l ne r ab l e and in e x t r eme circ um s t a n c e s may u n d e r g o l iquefaction. This phe n omen o n n e e d s to be t aken into cons i de r a t i on in eva lua t ing v ib ra t ions and expla in ing their effects [8 ] , [ 9 ] ( S e e a l so a nn ex A )
5 Quantity to be measured
The cha r a c t e r i z a t i on of both the n a t u r e of vibrat ion input and the r e s p o n s e may be effected by a var ie ty of d i s p l a c emen t , velocity or a c ce l e r a t i on t r a n s d u c e r s . T h e s e can furnish a r eco rd as a function of t ime . It is the u sua l p rac t i ce to s e n s e a k inemat ic quant i ty , s u ch as velocity o r a c ce l e r a t i on . From knowledge of the a pp r op r i a t e t r ans fe r function of the s e n s i n g s y s t em , e a c h quant i ty can be de r ived from ano t h e r by in tegra t ion or differentiation. In tegra t ion a t lower f r equenc i e s cal ls for c a r e and conf idence in amp l i t u d e p h a s e r e s p o n s e of t he t r a n s d u c e r and i n s t rumen t cha in ( s e e c l a u s e 6). As long as t he re qu i r emen t on d a t a col lect ion , t r e a tmen t and p r e s en ta t ion ( s e e c l a u s e 6 ) c an be met , t he s e n s o r may r e s p ond t o any c h o s e n quant i ty . Expe r i enc e sug g e s t s tha t t h e r e a r e p re fe r r ed m e a s u r i n g quan t i t i e s for different s i tua t ions ( s e e t a b l e 1).
1 ) Soil c omp a c t i o n m a y be mon i t o r e d by p r e c i s e l eve l l ing
6 Measuring Instrumentation
6.1 G e n e r a l r e q u i r e m e n t s
Vibration is m e a s u r e d with a view to us ing the da ta in s om e eva lua to ry or d i agnos t i c p r o c e du r e or to moni tor ing a vibrat ion with s om e e s t a b l i s h ed t a rge t level in mind. For eva lua t ion , the min imum perf o rmance shal l be sufficient to mee t the r equ i re men t s laid down in c l a u s e 3 and c l a u s e 7 with r e g a r d to the eva lua to ry p r o c e d u r e s d e s c r i b ed in c l a u s e 9.
It is not e x p e c t e d tha t a s ing le i n s t rumen ta t i on sy s tem would me e t all t he r e q u i r emen t s of f requency and dynamic r a n g e for the wide r a ng e of s t r u c t u r e s and inputs for which this In terna t ional S t a nda r d is app l i cab le .
The me a s u r i n g s y s t em inc ludes the following in s t rumen ta t i on :
— t r a n s d u c e r s ( s e e 6.2);
— s igna l condi t ion ing equ i pmen t ,
— da ta r eco rd ing s y s t em .
The f requency r e s p o n s e cha r a c t e r i s t i c s (ampl i tude and ph a s e ) n e ed to be specif ied for the comp l e t e me a s u r i n g s y s t em when c onne c t e d t og e t h e r in the m a n n e r t o be u s ed .
The d e g r e e to which m e a s u r e d motion n e e d s to ap p roach t rue motion will d e p e n d upon the c h a r a c t e r of the inves t iga t ion and the eva lua t ion me thod u sed .
The min imum r equ i r emen t for 9.2.2 and 9.2.3 is that the vibrat ion shal l be c h a r a c t e r i z e d by a con t i nuous m e a s u r em e n t of the p e ak par t ic le velocity va l ue s .
The min imum r equ i r emen t for 9.2.4 is that the t ime history of the vibrat ion shal l be r e co rded ove r suffic ient dura t ion and with sufficient a c cu r a c y to e s t a b lish its spec t r a l c ha r a c t e r i s t i c s . Analog or digital m e t h o d s a r e ava i l ab l e subject t o the s t ipula t ions laid down in this c l a u s e .
6.2 C h o i c e o f t r a n s d u c e r s
The cho i ce of t r a n s d u c e r s is impor tan t for the correct eva lua t ion of v ibra tory motion. In g ene r a l , t r a n s d u c e r s may be divided into two g r oup s producing a l inear ou tput e i the r a bov e or be low the natural r e s o n a n c e of t he s e n s i ng me c h a n i sm . The soca l led "velocity p ickup" or " g e o p h o n e " widely u s ed in s t ruc tu ra l vibrat ion m e a s u r em e n t is typical of an e l e c t r omagne t i c s e n s o r ope r a t i ng at a freq u en cy a bov e its na tu ra l r e s o n a n c e , w h e r e a s a p iezoe lec t r i c a c c e l e r ome t e r usua l ly o p e r a t e s be low
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Table 1 — Typical range of structural r e s p o n s e for various s o u r c e s
Vibration forcing function
Traffic road , rail, g r o u n d b o r n e
Blas t ing v ib r a t i on g r o u n d b o r n e
Pile dr iv ing g r o u n d b o r n e
Mach i n e r y o u t s i d e g r o u n d b o r n e
Acous t i c traffic, m a c h i n e r y o u t s i d e
Air ove r p r e s s u r e
Mach ine ry i n s i d e
Human ac t iv i t i e s a) impac t b) d i r ec t
E a r t h q u a k e s
Wind
Acous t i c Ins ide
Frequency range
Hz
1 to 80
1 to 300
1 to 100
1 to 300
10 to 250
1 to 40
1 to 1 000
0,1 to 100 0,1 to 12
0,1 to 30
0,1 to 10
5 to 500
Ampl i tude range
µm
1 to 200
100 to 2 500
10 to 50
10 to 1 000
1 to 1 100
1 to 100
100 to 500 100 to 5 000
10 to 105
10 to 105
Particle ve loc i ty
range
mm / s
0,2 to 50
0,2 to 500
0,2 to 50
0.2 to 50
0,2 to 30
0,2 to 30
0,2 to 20 0,2 to 5
0,2 to 400
Particle acce lerat ion
range
m / s 2
0,02 to 1
0,02 to 50
0,02 to 2
0,02 to 1
0,02 to 1
0,02 to 1
0,02 to 5 0,02 to 0,2
0,02 to 20
Time charac-terist ic
C/T
T
T
C/T
C
T
C/T
T
T
T
Measuring quant i t ies
pv th
pv th
pv th
p v t h / a t h
p v t h / a t h
pv th
p v t h / a t h
p v t h / a t h
pv t h / a t h
ath
Key
C = c o n t i n u o u s ( simplified c a t e g o r i e s , s e e 3 1 and 3 2 ) T = t r a n s i e n t
pv th = pa r t i c l e ve loc i ty t ime h i s t o ry a th = a c c e l e r a t i o n t ime h i s t o ry
NOTES
1 The r a n g e s q u o t e d a r e e x t r e m e s but i n d i c a t e t h e v a l u e s which m a y b e e x p e r i e n c e d and which m a y h a v e t o b e m e a s u r e d ( s e e a l s o n o t e 3). Ex t r eme r a n g e s o f amp l i t u d e o f d i s p l a c eme n t and f r e quency h a v e not b e e n u s e d t o d e r i v e p a r t i c l e ve loc i ty a nd a c c e l e r a t i o n .
2 Th e f r e quency r a n g e q u o t e d r e f e r s to t h e r e s p o n s e o f bu i ld ings and bui ld ing e l em e n t s to t h e pa r t i cu l a r t y p e o f exc i t a t ion . It is i nd i c a t i v e only
3 Vibra t ion v a l u e s within t h e r a n g e s g i v en m a y c a u s e c o n c e r n . T h e r e a r e no s t a n d a r d s which c o v e r all v a r i e t i e s o f bui lding, cond i t i on a n d d u r a t i o n o f e x p o s u r e , but m a n y na t i ona l c o d e s a s s o c i a t e t h e t h r e s h o l d o f v i s ib le e f fec ts with p e a k pa r t i c l e v e l o c i t i e s at t h e f ounda t i on of a bu i ld ing of m o r e t h an a few m i l l ime t r e s p e r s e c o nd . A s ignif icant p robab i l i t y o f s o m e d a m a g e i s l inked t o p e a k p a r t i c l e v e l o c i t i e s o f s e v e r a l h u n d r e d m i l l ime t r e s p e r s e c o n d . Vibra t ion l e v e l s be low t he t h r e s ho l d o f h um a n p e r c e p t i o n ( s e e ISO 26312) m a y be o f c o n c e r n in d e l i c a t e and indus t r i a l p r o c e s s e s .
the resonance. There are electromagnetic sensors which operate below their natural frequency, such as are widely used strongmotion seismographs.
In practice, care should be exercised in using the phase information from the "velocity pickup" type of transducer at the lower frequencies. If both am
plitude and phase response are critical, linear performance of the whole measuring chain should be ensured. A lowfrequency cutoff ten times the lowest required measured frequency is often recommended as a good compromise and, in general, the measured signal should be 5 dB above the background noise.
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Velocity p ickups g e n e r a t e a re la t ively high s igna l t h u s simplifying t h e i n s t r umen t cha in . If par t i c le ve locity i s n e e d e d , t h e p l ezo e l ec t r i c a c c e l e r ome t e r ou tpu t n e e d s i n t eg ra t i ng , and with t r a n s i e n t s t h e r e s p o n s e o f t h e who l e cha in shou ld be verified.
6.3 S i g n a l - t o - n o i s e r a t i o
The s igna l t o no i s e ra t io shou ld gene r a l l y be not l e s s t han 5 dB. If t he s igna l to no i s e rat io is b e twe en 10 dB and 5 dB, t h e m e a s u r e d va lue shou ld be corr e c t ed (i.e. d imin i shed ) and the co r rec t ion me t hod r epo r t ed . Ba ckg round no i s e i s def ined as the s um of all t h e s i gna l s not d u e to t he p h e n om e n o n und e r inves t iga t ion .
7 P o s i t i o n a n d f i x i n g o f t r a n s d u c e r s
7.1 P o s i t i o n s
7.1.1 General
The p r op e r cha r a c t e r i z a t i o n of t he vibrat ion of a building r e qu i r e s a n umb e r of pos i t i ons of m e a s u r emen t which d e p e n d upon the s i ze and complex i ty of the building.
Whe r e t he p u r p o s e i s to mon i to r with r e g a r d to impo s e d vibrat ion, t he p re fe r r ed posi t ion is a t t he foundat ion , a typical locat ion be ing at a point low on the main l o ad bea r i ng ex t e rna l wall a t g round floor level wh en m e a s u r em e n t s on the founda t ions p r ope r a r e not po s s i b l e
M e a s u r em e n t s of vibrat ion r e s p o n s e g e n e r a t e d by traffic, piledriving and b las t ing , e spec i a l l y at a g r e a t d i s t a n c e , s how that the vibrat ion may be amplif ied within the building and in p ropor t ion to the he ight of the bui lding. It may , the re fo re , be n e c e s s a r y to ca r ry out s imu l t a n e o u s m e a s u r em e n t s a t s e v e r a l po in t s within the bui lding. S imu l t a n e ou s m e a s u r e men t s on t he foundat ion and the g round ou t s i d e will s e r v e to e s t ab l i s h a t r ans fe r function
Whe r e a bui lding is h ighe r than 4 floors (≈ 12 m), s u b s e q u e n t m e a s u r i n g po in ts shou ld be a d d e d every 4 floors and at t h e h ighes t floor of the building.
Whe r e a building is mo r e than 10 m long, m e a s u r i n g pos i t ions shou ld be ins ta l led a t hor izonta l in te rva l s of a pp rox ima t e l y 10 m.
Addit ional m e a s u r i n g poin ts may h av e t o be m a d e in r e s p o n s e to r e q u e s t s by o c c u p a n t s and as a cons e q u e n c e of initial o b s e r v a t i o n s .
For i nves t i ga t ions of t h e ana ly t ica l type , pos i t ioning will d e p e n d upon t he m o d e s of de fo rma t ion to be c on s i d e r e d . Most p rac t ica l c a s e s a r e e conomica l l y l imited to identification of f undamen t a l m o d e s and
m e a s u r em e n t of max imum r e s p o n s e s in t h e who l e s t r u c t u r e t o g e t h e r with o b s e r v a t i o n s on e l eme n t s s uch a s floors, wal l s and w indows .
7.1.2 Measurement in a building
T r a n s d u c e r p l a c emen t in a building d e p e n d s on the vibrat ion r e s p o n s e of c onc e r n . As d e s c r i b e d in 7.1.1, a s s e s s m e n t of the vibrat ion be ing input to a building from g r ound bo r ne s o u r c e s is bes t d o n e by m e a s u r em e n t s on o r n e a r the foundat ion. De te rmi nat ion of s t ruc tura l racking or of s h e a r de fo rmat ion of t he building as a who le r equ i r e s m e a s u r em e n t s direct ly on the l oad bea r i ng m em b e r s which afford t he s t r u c t u r e s ' st iffness. This usual ly m e a n s t h r e e c ompo n e n t s of m e a s u r em e n t in c o r n e r s , a l though o t h e r a r r a n g em e n t s a r e pos s ib l e .
S ome t im e s , floor or wall mo t ions a r e of conce rn , with max imum amp l i t u d e s a t m id span loca t ions . Al though s om e t im e s very s e v e r e , t h e s e v ib ra t ions a r e usua l ly un re l a t ed to s t ruc tu ra l integrity. [ 1 1 ]
Inves t iga t ions a s s o c i a t e d with s o u r c e s within a building usual ly involve a t r i a l ande r ro r exp lo ra to ry p h a s e
In c a s e s wh e r e m e a s u r em e n t s r e l a t ed to e qu i pmen t a r e t o be m a d e , s uch a s when moni tor ing compu t e r s , r e l ays and o t h e r ins ta l l a t ions s ens i t i v e to vibra t ion, the m e a s u r em e n t shou ld reflect the incoming vibra t ion. The point of m e a s u r em e n t shou ld be p l aced on or a t t he foundat ion or on the f rame of t h e e q u i pmen t In this c a s e , the e qu i pmen t shou ld if po s s i b l e be swi t ched off for t he m e a s u r e men t .
In c a s e s wh e r e m e a s u r em e n t s r e l a t ed to g roundt r an smi t t ed vibrat ion a r e t o be m a d e , such a s wh e r e g round vibrat ion s o u r c e s a r e be ing s tud ied , i t is u sua l to o r i en t a t e the s e n s o r s with r e s p e c t to radia l d i rec t ion def ined as the line joining the s o u r c e and the s e n s o r . When s tudying s t ruc tura l r e s p o n s e t o g round vibrat ion, i t is mo r e rea l i s t i c to o r i en t a t e with r e s p e c t to t he major and minor a x e s of the s t r uc tu r e . It is often not po s s i b l e to mak e m e a s u r em e n t s at the foundat ion p r ope r so i n s t r umen t s h ave to be coupled to t he g round .
Vibration m e a s u r em e n t s m a d e on o r be low the g round su r f ace may be affected by the var ia t ion of the amp l i t ude of a su r f ace w av e with the dep th Building founda t ions may then be e x p o s e d to a motion which is different from the o n e o b s e r v e d on the g round su r f ace d e p e n d i n g on the wave l eng t h , founda t ion d e p t h s and g eo t e chn i c a l cond i t ions .
For w ind induced vibra t ion, ver t ical c ompo n e n t s a r e often d i s p e n s e d with and tes t i n s t rumen t d ispos i t ion shou ld be m a d e with ro ta t iona l and t r ans l a t iona l m o d e s in mind.
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7.2 Fix ing of t r a n s d u c e r s
7.2.1 Coupling to structural e l e m e n t s
The moun t ing of v ibra t ion t r a n s d u c e r s to v ibra t ing e l emen t s or s u b s t r a t e shou ld comply with ISO 5348 with r e g a rd to a c c e l e r ome t e r s . The a im shou ld be to r e p r o du c e faithfully t h e mot ion of t h e e l emen t or s u b s t r a t e without in t roduc ing addi t ional r e s p o n s e . C a r e shou ld be t aken with triaxial a s s emb l i e s to avoid rocking or bend ing .
The m a s s of t h e t r a n s d u c e r and moni tor ing unit (if any) shal l not be g r e a t e r than 10 % of t h e building e l emen t to which it is fixed. Mount ing shal l be as stiff and a s light a s po s s i b l e .
B racke t s shou ld be avo ided . It is be t t e r to fix t h r e e uniaxial t r a n s d u c e r s to t h r e e faces of a me ta l c u b e rigidly moun t ed by m e a n s of s t ud s or quickse t t ing , high modu l u s res in . The t r a n s d u c e r moun t ing can be s e c u r e d to the f rame of t he building by e xp an s i on bolts. Gypsum joints a r e p re fe r red when me a s u r i n g on l ightweight c o n c r e t e e l emen t s .
In spec ia l c i r c ums t a n c e s , it is a c c e p t a b l e to g lue the t r a n s du c e r or a t t ach i t us ing magne t i c a t t rac t ion . For m e a s u r em e n t s i ndoors on hor izonta l s u r f a ce s , doub le s ided a dh e s i v e t a p e may be u s ed on all ha rd su r f ace s for a c c e l e r a t i o n s be low 1 m / s 2 , a l though mechan i c a l fixings a r e p re fe r red .
M e a s u r em e n t s on floors having compl i an t c ove r i ng s t end to give d is tor ted r e su l t s and shou ld be avo ided . Whe re i t is not po s s i b l e to r e l oca t e the t r a n s d u c e r s , c ompa r a t i v e m e a s u r em e n t s with different m a s s and coupl ing condi t ions for the mount ing block shou ld be m a d e to eva lua t e the effect of the compl i an t cove r ings
7.2.2 Coupling to the ground
Soil cond i t ions permit t ing , the t r a n s d u c e r may be fixed to a stiff s t ee l rod (having a d i ame t e r of not l e s s t han 10 mm) , dr iven th rough a l oose su r f ace layer. This rod should not project mo r e than a few mi l l imet res a b ov e g round su r face . C a r e should be t aken t o e n s u r e c l o s e con tac t b e twe en t h e t r a n s d u c e r and the g round . In c a s e s w h e r e a c ce l e r ation g r e a t e r than 2 m / s 2 is e xpe c t e d , a firm g round mount ing i s n e e d e d to p r even t s l i ppage . Whe r e t r a n s d u c e r s h ave to be moun t e d in the g round in o r d e r to min imize coupl ing dis tor t ion, they shou ld be bur ied .
Whe r e t r a n s d u c e r s h a v e to be moun t e d in t h e g round , in o r d e r to min imize coupl ing dis tor t ion, they should be bur ied to a dep th a t l eas t t h r e e t ime s the main d imens ion of t he t r a n s du c e r /moun t i n g unit. Alternat ively, they c an be fixed to a rigid su r f a ce p la te with a m a s s ra t io (m/pr 3 ) not mo r e t h an 2,
w h e r e m i s t h e m a s s o f t h e t r a n s d u c e r and p la t e and r is t he equ iva l en t r ad i u s of t h e p la te . The rigid surface p la te may , for e x amp l e , be a we l l bedded paving s l ab . For mos t so i l s , t h e m a s s dens i ty , p , r a n g e s from 1 500 kg/m3 to 2 600 kg /m3 .
8 Data collection, reduction and analysis
8.1 General
The aim of m e a s u r em e n t is to a cqu i r e sufficient information to e n a b l e the s e l e c t e d me thod of evaluat ion ( s e e c l a u s e 9) to be ca r r i ed out with a sufficient d e g r e e of conf idence .
The amoun t of information r equ i r ed to c h a r a c t e r i z e vibrat ion p roper ly i n c r e a s e s as t he complexi ty of the vibrat ion i n c r e a s e s from s imp le per iod ic to nons t a t iona ry r a ndom and t r ans i en t mot ion.
Data col lect ion s y s t em s which a r e a d e q u a t e for de fining a per iodic motion ove r a specif ied f requency r a n g e may not be a d e q u a t e for e s t ab l i sh ing even a s ing le p a r am e t e r index (for e x amp l e p e ak part ic le velocity) for a mo r e comp lex motion.
8.2 D e s c r i p t i o n o f d a t a
Any da ta resu l t ing from the obse rva t i on of a physical p r o c e s s can broadly be d e s c r i b ed a s de t e rmin i s t i c o r r a n dom . Dete rmin is t i c da t a a r e t h o s e that c an be d e s c r i b ed by an explicit ma t h ema t i c a l function.
Figure 1 i l lus t ra tes c a t e go r i e s of t he t ype s of da ta tha t may be e n coun t e r e d . A desc r ip t ion of e a ch catego ry is given in ISO 2041.
8.3 D a t a a n a l y s i s p r o c e d u r e s
Having dec ided into which of t h e main c a t e go r i e s illus t ra ted in figure 1 the da t a fall, the type of ana ly s i s will normal ly be appa r en t . If the d a t a is c a t ego r i z ed as de te rmin i s t i c , t hen a s imp le ana ly s i s (r .m.s . , peak to peak , m e a n s qua r e ) will often suffice.
If the spec ia l c a s e of nonpe r iod ic de t e rmin i s t i c da ta , p e ak amp l i t ude shou ld be d e t e rm in ed without p recondi t ion ing (a l though a d.c. c omponen t may be c omp e n s a t e d by ana ly s i s of a sec t ion of the record prior to c ap t u r e of the s ignal) . Detai ls a r e given in [ 10 ] and [ 12 ] . A dynamic r a n g e of 40 dB is a d e qu a t e for mos t p u r p o s e s , but 50 dB is p re fe r red .
R andom da ta should be t e s t ed for s ta t ionar i ty ( s e e [13]) .
I f t he da t a a r e d e em e d to be s t a t ionary , t h e p roce d u r e s out l ined in a n n e x C a r e a pp r op r i a t e and a r e d e s c r i b ed in mo r e detai l in [ 1 0 ] , [ 1 2 ] , [ 1 3 ] and [14].
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b) Random data
Figure 1 — Categories of the types of data
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9 Method of data evaluation
9.1 General
Evaluation of measurements should reflect both the purpose of those measurements and the type of Investigation.
A full response analysis for predictive purposes requires Information on structural details and conditions not usually readily obtainable. An investigator may, therefore, need to have an appropriate method of assess ing the severity of vibration of a structure or a component with regard to the probability of damage. In such an assessment , the following factors need to be taken into account:
a) resonant frequencies of basic structure and component parts (walls, floors, windows);
b) damping characteristics of basic structure and component parts;
c) type of construction, its condition and material properties;
d) spectral structural features;
e) characteristics of excitation;
f) deflected form;
g) nonlinearity in amplitude response.
Although this International Standard is primarily concerned with the measurement and evaluation of the response, the chain of action, source, transmission path and transferfunction have to be borne in mind when evaluation is being made.
9.2 Types of Investigation
For many of the parameters of interest, listed in 9.1 a) to g), the choice of instrumentation, its location within the building, the type of recording device and the number of data channels or measurement points desired, the duration of monitoring for the phenomena and the speed of data collection will immediately be decided. The outlining of instrumentation requirements in clause 6 and annex C has been arranged in such a way as to facilitate the selection of instrumentation to meet particular requirements. Beyond this it is important to delineate the degree of sophistication to be applied to the Investigation. Instruments which characterize the vibration environment by a single quantity, such as those used in connection with human response and machine condition, may be used in a preliminary survey so long as the limited frequency responses are taken into account. For the purposes of this International Standard, a preliminary assessment , a monitoring pro
gram, a field survey and a detailed engineering analysis are under consideration.
9.2.1 Preliminary assessment
Situations may arise where an assessment has to be made of vibration problems by desk study alone, usually before field measurements . Empirical methods can be used to estimate response provided that data on the source parameters and building response characteristics, such as fundamental frequency and damping, are available.
9.2.2 Exploratory monitoring
Very limited measurement of vibration on a building or over an area can indicate the existence of a problem requiring further investigation. High errors are not uncommon and this fact has to be kept in mind (See also final paragraph in 9.2.3)
9.2.3 Field survey
A field survey would consist of a limited number (see also 7.1) of vibration measurement locations in order to a s se s s the vibration severity often in comparison with values stipulated in codes or regulations.
In the case of vibrations which can be reproduced for a sufficient time, the same transducers can be used for the different points keeping a reference point at the foundation level near source.
As regards exploratory monitoring (see 9 2 2) and field surveys, measurements should be of an accuracy compatible with the uncertainties implicit in the vibration indices and empirical relationship used Single parameter indices, such as peak particle velocity or peak acceleration and r.m.s values, need, generally, only to be known to within ± 10 % at the 68 % confidence level
9.2.4 Engineering analysis
When complex structures of vital importance are being subjected to vibration excitation of a magnitude that requires serious consideration of the consequences , the structural behaviour needs to be assessed in a more detailed way.
Instrumentation for monitoring the time history should be mounted at a number of locations to ensure that specific values for that structure are not exceeded.
If the groundtofoundation transfer function is of concern, simultaneous recording outside and on the foundation should be carried out. The recording position on the foundation is at a point on the main wall at ground floor level or the basement.
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The n umb e r o f m e a s u r i n g po in t s a n d the i r locat ion h a v e t o be def ined and modif ied a c co r d i ng t o the c h a r a c t e r i s t i c s o f t h e bui lding and t he o b s e r v a t i o n s no t iced du r ing moni to r ing .
The na tu ra l f r equenc i e s of bu i ld ings shou ld be de t e rm ined , if p o s s i b l e .
In the c a s e of v ib ra t ions which can be r e p r o d u c e d for a sufficient t ime , the s a m e t r a n s d u c e r s c an be u s ed for t he different poin ts k eep ing a r e f e r ence point a t t he foundat ion level n e a r the s o u r c e .
For s t r u c t u r e s of vital impo r t a n c e , r e s p o n s e ana ly s i s shou ld be ca r r i ed out as well as an e s t ima t e of s t r u c t u r e load ing . A full e ng i n e e r i n g ana l y s i s requ i r e s a s y s t em which would e n a b l e f r equency to be e s t ima t e d to ± 1 % and d amp i ng to ± 10 %.
9.3 R e p o r t i n g o f c o n t r o l a c t i v i t i e s
The style of r epor t ing shou ld be con s i s t e n t with the type of inves t iga t ion ( s e e 9 2), but as a m in imum the repor t shou ld inc lude the following:
a) Risk ana l y s i s
1) Descr ip t ion of the s o u r c e
2) Type and condi t ion of bui lding, in a c c o r d a n c e with a n n e x A.
3) P u r p o s e of the m e a s u r em e n t .
4) Re f e r e n c e to the s t a n d a r d be ing u s ed and type of inves t iga t ion
b) M e a s u r em e n t s
1) Posi t ion of t r a n s d u c e r and m a n n e r of coupl ing
2) Type and m a k e of t r a n s du c e r , s igna l condi t ioning and r e co rd ing e q u i pmen t
3) Cal ibra t ion factors for the i n s t r umen t a t i on s y s t em
4) F r equency r a n g e and l ineari ty
5) A s s e s sm e n t of t he s o u r c e s of e r ror .
6) — For mon i to r ing or su rvey inves t iga t ion ( s e e 9.2.2 and 9.2.3), it is sufficient to m a k e cont i nuous r eg i s t r a t i ons of p e a k par t ic le velocity v a l u e s .
— For further inves t iga t ion ( s e e 9.2.4), a per ma n e n t r e co rd of t ime his tory shou ld be m a d e ava i l ab l e .
c) Building inspec t ion
1) Inspec t ion of bui ld ings before v ibra t ion e xpo s u r e , with g raph ica l r epor t ing of c r a ck s and o t h e r d a m a g e .
2) Inspec t ion of the s am e bui ld ings after t h e vibra t ion e x p o s u r e .
3) Eva lua t ion of o b s e r v e d d am a g e
d) Re f e r e n c e to o t he r r e l evan t In ternat ional S tand a r d s .
9.4 E v a l u a t i o n for p r e d i c t i o n
An exis t ing building may be e x po s e d to a new s ou r c e , ex t e rna l o r in terna l , and s om e a s s e s sm e n t of the e x p e c t e d v ibra t ion r e s p o n s e is n e e d ed . Given sufficient informat ion abou t t he cha r ac t e r i s t i c s of the input and the p r ope r t i e s of the s t ruc tu re , numer ica l a n a l y s e s us ing o n e o r o t h e r well known t e chn i que s of r e s p o n s e s p e c t r a , Four ie r r e s p o n s e , t ime s t ep int eg r a t i on [ 1 5 ] may be u s ed for impor tan t bui ldings . Alternat ively, a cha r a c t e r i s t i c index, such as a k inemat i c quant i ty ( d i s p l a c emen t , velocity, acce le r ation) ( s e e 9.6), c an be r e l a t ed to e xpec t ed perf o rmance us ing empi r i ca l da t a a pp rop r i a t e to the type of building. [7]
A conven i en t way of e x p r e s s i n g a vibrat ion in the f requency doma i n i s the " r e s p o n s e s p e c t r um" , widely u s ed in eng inee r i ng . [ 7 ] ( S e e IEC 68227 ) For the spec i a l c a s e of z e r o d amp ing , i t is c l o s e to the Four ier amp l i t ude s p e c t r um .
In mos t c a s e s , the r e s p o n s e c h a r a c t e r i s t i c s of the s t ruc tu re a r e ill def ined a l though dynam i c tes t proc e d u r e s a r e now ava i l ab l e . [ 7 ]
9.5 E v a l u a t i o n for v i b r a t i o n s t u d y in e x i s t i n g b u i l d i n g s
The eva lua t i on of vibrat ion s t a t u s in exis t ing bui ld ings may be ca r r i ed out at different leve ls of soph i s t i ca t ion cons i s t en t with the inves t iga t ive proc e d u r e s ou t l ined in 92 Indica t ions of vibrat ion se verity may be in t e rm s of s t r e s s e s or k inemat i c quan t i t i e s In s om e c a s e s , the direct ob s e rva t i on of c r ack op en i ng or ex t en s i on affords va luab l e informat ion on the r e s p o n s e and may ind ica te p r og r e s s ive de t e r i o r a t i on . [15], [16]
9.6 K i n e m a t i c q u a n t i t i e s a s i n d i c e s o f v i b r a t i o n s e v e r i t y i n s t r u c t u r e s
For s e v e r a l d e c a d e s s t ud i e s h ave b e en ca r r i ed out to r e l a t e the vibrat ion sever i ty in t e rm s of a quant i ty such a s p e a k d i s p l a c emen t , veloci ty, a c ce l e r a t i on , r e l a t ed to vis ible effects on s t r u c t u r e s .
Whe r e m e a s u r em e n t s a r e m a d e upon a c omponen t , a k inema t i c quant i ty , s uch as p e ak velocity, can be
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expressed as a s t ress (see annex B) and, in turn, related In structural terms to allowable stress. When the kinematic quantity refers to wholebody structural response measured at some chosen position, the response frequency and damping of the structure, and duration of the input affect vibration severity. The kinematic quantity is then an empirical index and shall be qualified by the kind of building to which it refers (see 3.3).
Some account of these factors is embodied in the use of the peak spectral acceleration or velocity as a damage index [6],[11] applicable to lowrise (one to three storeys high) and "whole" building response. [16]
The dependence of severity rating on response frequency of both building and frequency content of the excitation is also recognized in the empirical correlations which strictly apply to buildings with a limited range of fundamental frequency in shear, and identify different severity ratings in different frequency bands. A broad guide to vibration levels of interest is given in table 1.
9.7 Probabilistic a s p e c t s
There is increasing evidence that the criteria relating vibration to visible effects on buildings (cosmetic, minor and major damage) should be approached in a probabilistic way.
For possible combinations of age and condition of a building, it may not be possible to establish an economic absolute lower limit.
This is particularly the case where either a peak kinematic value (usually particle velocity) of ground motion within a specified frequency band or a peak spectral velocity response spectrum acceleration or displacement is being used as an index of damage potential Minimal risk for a named effect is usually taken as a 95 % probability of no effect.
The evaluation of the response of a building or component part may be assisted by measurements
2) See ISO 4358.
10
of local strain or relative displacement (for example crack monitoring), although this would not constitute a measure of vibration status. It may, however, permit (with difficulty) a direct evaluation of composed dynamic stress for comparison with design criteria.
9.8 Fatigue factors
Repeated stress reversal over many cycles carries a risk of increasing fatigue failure. Reference for steel members can be made to appropriate design codes. Such guidance is not available for concrete, masonry and other building materials. Reference would have to be made to research. Longterm, lowlevel vibration amounting to 1010 load reversals may have to be taken into account for special structures, monuments, etc. [17]
9.9 Description of d a m a g e
For the purposes of this International Standard, the damage is classified into the following categories:
— Cosmetic
The formation of hairline cracks2) [21] on drywall surfaces, or the growth of existing cracks in plaster or drywall surfaces; in addition, the formation of hairline cracks in mortar joints of brick/concrete block construction.
— Minor
The formation of large cracks or loosening and falling of plaster or drywall surfaces, or cracks through bricks/concrete blocks.
— Major
Damage to structural elements of the building, cracks in support columns, loosening of joints, splaying of masonry cracks, etc.
NOTE 2 The description of damage has its equivalent in the intensity scales used by seismologists.
IS 1 4 8 8 4 : 2 0 0 0 ISO 4 8 6 6 : 1990
Annex A (informative)
Classification of buildings
A.1 General
This a n n e x p rov ide s simplified and helpful gu ide l ines for classifying bui ld ings a c co rd ing to their p r obab l e r eac t ion t o mechan i c a l v ib ra t ions t r an s mitted by the g round .
A dynamic s y s t em , for the p u r p o s e s of this c l a s s i fication, c on s i s t s of the soil and strata, in which a r e se t the foundations (if exis t ing) , t o g e t h e r with the building structure itself.
Table A.2 g ives 14 simplified c l a s s e s taking into cons ide r a t i on the following factors:
— type of cons t ruc t ion (as a s c e r t a i n e d from tab le A.1);
— foundat ion ( s e e c l a u s e A.5);
— soil ( s e e c l a u s e A.6);
— political impo r t a n c e factor
The f requency r a ng e is t aken from 1 Hz to 150 Hz ( s e e a l s o 3.3), which c ov e r s mos t e v en t s met in indust r ia l p rac t i ce , b las t ing , piling and traffic. Shock directly in t roduced into the s t ruc tu re by industr ial mach i n e r y is not inc luded though its effects at s om e d i s t a n c e a r e . Shock p r oduced by blas t ing, piling and o the r s o u r c e s ou t s i d e the strict conf ines of the s t ruc tu re a r e not inc luded but the effects on the s t ruc tu re a r e . The bui ld ings refer red to exc lude very tall s t r u c t u r e s with mo r e than 10 s t o r ey s .
A.2 Structures Involved
A.2.1 The following s t r u c t u r e s a r e inc luded in the c lass i f icat ion.
— all bu i ld ings u s ed for living and working ( h ou s e s , offices, hosp i t a l s , s choo l s , p r i sons , factor ies , etc.) ;
— publicly u s e d bui ld ings (town hal ls , c h u r c h e s , t emp l e s , m o s q u e s , h e av i e r industr ia l milltype bui ld ings , etc.);
— elder ly , old and anc i en t bui ld ings of a rch i t ec tura l , a r cheo l og i c a l and his tor ica l va lue ;
— l ighter indust r ia l s t r u c t u r e s , often d e s i gn ed to the c o d e s of building p rac t i ce .
A.2 .2 The following s t r u c t u r e s a r e not inc luded in the c lass i f icat ion:
— heav i e r s t r u c t u r e s such as nuc l e a r r e a c t o r s and the i r ad junc t s and o t h e r heavy powe r p lan ts , rolling mills, h e av i e r chemica l e ng i n e e r i n g s t r u c t u r e s , all t ype s of d am s , and con ta in ing s t r u c t u r e s for fluids and g r anu l a r ma t e r i a l s , for e x amp l e wa t e r t owe r s and t anks , p e t r o l eum s t o r a g e , gra in and o t h e r s i los , e tc . ;
— all u n d e r g r o und s t r u c t u r e s ;
— all ma r i n e s t r u c t u r e s .
A.3 Definition of c l a s s e s (see table A.2)
The c l a s s e s a r e defined by taking as a r e f e r ence a well ma in t a i n ed building in good repa i r . The refere n c e building shal l not h ave any cons t ruc t iona l d e fects nor shal l i t h ave s u s t a i n ed acc iden t a l d am a g e from e a r t h q u a k e s . If t he cons t ruc t ion d o e s not fulfil t h e s e r e q u i r emen t s , i t shal l be a l loca ted to a lower c l a s s .
The o r d e r in which the s t ruc tura l t ype s a r e classif ied d e p e n d s on the i r r e s i s t a n c e to v ib ra t ions , and a l so on the t o l e r a n c e s that can be a c c e p t e d for the v ibra t ional effects on s t r u c t u r e s , given their architec tura l , a r cheo log i ca l and his tor ical va lue .
Th r e e impo r t an t e l emen t s e n t e r into the reac t ion of a s t r uc tu r e u nd e r t he effects of mech an i c a l vib r a t i ons . The t h r e e e l eme n t s a r e a s follows:
— the c a t e go r y of t he s t r uc tu r e — tab le A.1 g ives a p re l iminary classif icat ion of the c a t e g o r i e s of s t r u c t u r e s b a s e d on the g r oups def ined in c l a u s e A 4 ;
— the foundat ion ( s e e c l a u s e A.5);
— the n a t u r e of t he soil ( s e e c l a u s e A.6).
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A.4 C a t e g o r i e s of s tructures
A.4.1 Group 1 — Ancient and elderly buildings or traditionally built structures
The types of buildings considered in this group can be divided into the two following subgroups:
a) elderly, old or ancient buildings;
b) all modern buildings constructed in older, traditional style using traditional kinds of materials, methods and workmanship.
This group, generally, is of heavier construction and has a very high damping coefficient, for instance due to soft mortar or piaster. This group also includes traditionally resilient structures in earthquake zones. Buildings in this group seldom have more than six storeys.
A.4.2 Group 2 — Modern buildings and structures
The types of buildings considered in this group are all of modern structure using relatively hard materials tied together in all directions, usually light in weight overall, and with little damping coefficient.
This group includes frame buildings as well as calculated loadbearing wall kinds. Buildings vary from being single to multistorey. All types of cladding are included. This group also includes some older types of buildings which are constructed using modern materials, tying and damping.
A.5 C a t e g o r i e s o f f o u n d a t i o n s
A.5.1 Class A
Class A includes the following types of foundation:
— linked reinforced concrete and steel piles;
— stiff reinforced concrete raft;
— linked timber piles;
— gravity retaining wall.
A.5.2 Class B
Class B includes the following types of foundation:
— nontied reinforced concrete piles3);
— spread wall footing;
— timber piles and rafts.
A.5.3 Class C
Class C includes the following types of foundation:
— light retaining walls;
— large stone footing;
— no foundations — walls directly built on soil.
A.6 T y p e s of so i l
Soils are classified into the following types:
Type a: unfissured rocks or fairly solid rocks, slightly fissured or cemented sands;
Type b: compact, horizontal bedded soils;
Type c: poorly compacted, horizontal bedded soils;
Type d: sloping surfaces with potential slip planes;
Type e: open granular, sands, gravels (noncohesive), and cohesive saturated clays;
Type f: fill.
3) Piles, structurally connected, usually at level of pile caps.
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Table A.1 — Categorization of structures according to group of building
13
Category of structure
Res
ista
nce
to v
ibra
tion
decr
easi
ng
I
1
2
3
4
5
6
7
8
Group of building 1
Heavy industrial multistorey buildings, five to seven storeys high, including earthquakeresistant forms
Heavy structures, including bridges, fortresses, ramparts
Timber frame, heavy, public buildings, including earthquakeresistant forms
Timberframe, single and twostorey houses and buildings of associated uses, with infilling and/or cladding, including "log cabin" kinds, including earthquakeresistant forms
Fairly heavy multistorey buildings, used for medium warehousing or as living accommodation varying from five to seven storeys or more
Four to sixstorey houses, and buildings of associated urban uses, made with blockwork or brickwork, loadbearing walls of heavier construction, Including "stately homes" and small palacestyle buildings
Twostorey houses and buildings of associated uses, made of blockwork, brickwork or pisaterre, with timber floors and roof
Stone or brickbuilt towers, including earthquakeresistant forms
Lofty church, hall and similar stone or brickbuilt, arched or "articulated" type structures, with or without vaulting, including arched smaller churches and similar buildings
Low heavily constructed "open" (i.e. noncrossbraced) frame church and barn type buildings including stables, garages , low industrial buildings, town halls, temples, mosques, and similar buildings with fairly heavy timber roofs and floors
Ruins and nearruins and other buildings, all in a delicate s tate
All class 7 constructions of historical Importance
(see c lause A.4) 2
Two and threestorey industrial, heavyframe buildings of reinforced concrete or structural steel, clad with sheeting and/or infilling panels of blockwork, brickwork, or precast units, and with steel, precast or In situ concrete floors
Composite, structural steel and reinforced concrete heavy industrial buildings
Five to ninestorey (and more) blocks of flats, offices, hospitals, lightframe industrial buildings of reinforced concrete or structural steel, with infilling panels of blockwork, brickwork, or precast units, not designed to resist ear thquakes
Singlestorey moderately lightweight, opentype industrial buildings, braced by internal cross walls, of steel or aluminium or timber, or concreteframe, with light, sheetcladding, and light panelinfilling, including earthquakeresistant types
Twostorey, domestic houses and buildings of associated uses, constructed of reinforced blockwork, brickwork or precast units, and with reinforced floor and roof construction, or wholly of reinforced concrete or similar, all of earthquakeresistant types
Four to tenstorey domestic and similar buildings, constructed mainly of lightweight loadbearing blockwork and brickwork, calculated or uncalculated, braced mostly by internal walls of similar material, and by reinforced concrete, preformed or in situ floors at least on every other storey
Twostorey domestic houses and buildings of associated uses, including offices, constructed with walls of blockwork, brickwork, precast units, and with timber or precast or in situ floors and roof structures
Single and twostorey houses and buildings of associated uses , made of lighter construction, using lightweight materials, prefabricated or in situ, separately or mixed
IS 14884 : 2000 ISO 4866 : 1990
Table A.2 — Classification of buildings according to their resistance to vibration and the tolerance that can be accepted for vibrational effects
Class of building1)
Level of acceptable vibration
decreasing
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Category of structure (see table A.1)
1 2 3 4 5 6 7 8
Categories of foundations (capital letters) and types of soil (lower case letter) ( s ee clause A.5 and clause A.6 )
A a
A b A a
A b B a
A c B b
B e
A f
B f
A a
A b B a
B b
A c
A f
B f
A a
A b
A c
A d
A e
C f
A a A b
A c B a B b
B e
B d
B e
C f
B a
B b C a
B e C b
B e C c
C d
C e
C f
B a
B b C a
B c C b
B d C c
B e C d
C e
Cf
A a
A b
B a
B c C a
B d C b C c
C d C e C f
1) High class number high degree of protection required.
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IS 14884 : 2000 ISO 4866 : 1990
Annex B (informative)
Estimation of peak stress from peak particle velocity
The s t r e s s e s in b e a m s o r p l a t e s v ibra t ing c l o s e to r e s o n a n c e can be c a l cu l a t ed from m e a s u r em e n t o f velocity or d i s p l a c emen t and f requency , if t he m e a s u r em e n t is p e r fo rmed at t h e poin ts of maximum vibra t ing d i s p l a c emen t s . In this c a s e a knowl e dge of t h e b ounda r y cond i t i ons and t he stiffness is not n e c e s s a r y for e s t ima t i ng the s t r e s s e s .
For b e a m s with full r e c t a ngu l a r c r o s s s e c t i on and con s t an t st iffness and weigh t load ing , the following r e l a t i onsh ip app l i e s , i n d ep end en t of t he length , he ight and width o f t h e b e am , b e twe e n the l a rge s t b end i ng s t r e s s σm a x , a nd t h e v ibra t ion veloci ty vmax.
w h e r e
max × ɷ is the maximum amplitude of the vibration velocity occurring at a point at
t he b e am length [wh e r e ɷ i s the forcing f requency app rox ima te ly equa l to ɷn (na tura l f requency of the b e am ) ] ;
Edyn i s t h e d yn am i c elas t ic i ty modu lu s ;
p is t h e m a s s dens i ty ;
i s t h e load coefficient, w h e r e the b e am is s t r e s s e d by o the r even ly dis t r ibuted l o ad s in addi t ion to its own weight (G t o t = G b e am + G o t h e r l o a d s ) ;
kn is t h e m o d e coefficient ( d imens ion l e s s ) , 1 to 1,33; the e i g e nmo d e coefficient kn d e p e n d s on the bounda ry condi t ions and the d e g r e e of the mode , which only h a s a slight inf luence.
For further de t a i l s , s e e [ 18 ] .
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IS 14884 : 2000 ISO 4866 : 1990
Annex C (informative)
Random data
C.1 General
Random data may be encountered in practice (wind loading, crusher machinery). Spectral analysis techniques can be used to estimate response characteristics. The estimate may be more or less precise depending on the structural characteristics (frequency and damping of a selected mode) and the precision required of the analysis.[14] Two kinds of error, bias and variance, are involved. [14] Choice of recording duration depends on the permissible errors chosen. If bias error is to be 4 % and variance error 10 %, for example, the recording duration, Tr, in seconds, may be calculated using the following common formula:
where η
fn
is the modal damping ratio;
is the natural frequency of mode n, under consideration, in hertz.
For instance, if η = 1 % of critical and fn = 1 Hz, then a recording duration of 20 000 s is needed to estimate to the bias and variance errors selected above. If η is 2 % of critical and fn is 10 Hz, a recording duration of 1 000 s is needed. Acceptance of higher errors would reduce the required recording duration.
These requirements are independent of the type of equipment used for analysis. (It is common practice to use magnetic type recorders) Structural damping
will be dealt with in a future addendum to this International Standard.
Nonstationary random data presents special problems and reference should be made to appropriate literature; see [ 1 4 ] .
The analysis of random data is conducted in one of two domains, frequency and time, and these are considered in clause C.2 and clause C.3.
C.2 Frequency domain
In general vibration analysis, the quantity most often used is the Power Spectral Density (PSD). In the analysis of structural vibration, the amplitude spectral density itself may be presented. Other types of analysis in this domain include transfer function, cross PSD, coherence function, and quadrate spectral density. These results are presented as the "physical quantity" squared per hertz versus frequency, respectively as dimensionless numbers and ratios of physical quantities.
C.3 Time domain
In the time domain covariance, autocorrelation, crosscorrelation, and covariance analyses may be carried out. The autocorrelation function, which is the inverse of the power spectrum, is the most commonly used. Many of the quantities in the time domain can be used with deterministic data. However, the more complex functions are often used with random data. Timedomain analysis covers mean, rootmeansquare, peak counting, zero crossing counting as well as probability density, probability distribution, skewness and Kurtosis.
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IS 14884 : 2000 ISO 4866 : 1990
Annex D (informative)
Bibliography
[ 1 ] BROCH, J.T. Mechanical Vibration and Shock, Brüel & Kjær, Næ rum , Denmark , 1972.
[ 2 ] JEARY, A.P. Pr ivate c ommun i c a t i o n Building Research Establishment Note, 1980.
[ 3 ] Appl ied Techno logy Counci l , Tentative provisions for the development of seismic regulations for buildings (ATC Spec ia l Publ icat ion 3.06; NBS Spec ia l Publ ica t ion 510; NSF Publica t ion 78.8, p. 56; NSF Publ ica t ion, pp. 6570, NSF Publ icat ion, pp. 381400), 1978.
[ 4 ] DIN 4149/1 , Bauten in deutschen Erdbebeng eb i e t e n ; Lastannahmen, Bemessung und Ausfuhrung übl icher Hochbauten (Bui ldings in G e rma n e a r t h q u a k e a r e a s ; d e s i gn l oads , a n a l y s i s and s t ruc tu ra l de s i gn ; unu sua l bui ldings) .
[ 5 ] DIN 4150/1 , Erschütterungen im Bauwesen, Grundsätze, Vorermittlung und Messung von SchwingungsgröBen (Vibrat ions in building; p r inc ip les , p r ede t e rm ina t i o n and m e a s u r e men t of the amp l i t ude of osc i l la t ions)
[ 6 ] MEDEARIS, K. Development of rational damage criteria for low rise structures subject to blasting vibrations, K.M. Assoc . Repor t , 1976.
[ 7 ] NEWMARK, M. and ROSENBLUTH, E. Fundamentals of earthquake engineering, Eag l ewood Cliffs, New J e r s e y P ren t i ce Hall, 1973.
[ 8 ] SEED , H.B. Soil l iquefact ion and cyclic mobility eva lua t ion for level g round dur ing e a r t h q u a k e . American Society of Civil Engineers, GT2, 1979, pp. 20125.
[ 9 ] PYKE, R , SEED, H.B and CHAN, C.K. S e t t l emen t o f s a n d s unde r mul t id i rec t iona l shak ing . American Society of Civil Engineers, GT4, pp. 379398.
[ 10 ] RABIMER, L.R. and GOLD, B. Theory and Application of Digital Signal Processing, Eag lewood Cliffs, New J e r s e y ; P ren t i ce Hall, 1974.
[11 ] SISKIND, D.E., STAGG, M.S., KOPP , J.W. and DOWDING, C.H. S t ruc tu r e r e s p o n s e and d am a g e p r oduc ed by g round vibrat ion from sur face m ine b las t ing; United S t a t e s Bu r e au of Mines . Report of Investigations No. RI. 8507, 1980.
[ 12 ] OTNES , R. and ENOCHSON, L. Digital Time Series Analysis, New York: John Wiley & Sons , 1972.
[ 13 ] BENDAT, J.S. and PIERSOL, A.G. Random data. Analysis and measurement procedures, New York: J ohn Wiley & Son s , 1971.
[ 14 ] OPPENHEIM, A.V. and SCHAFER, R W. Digital Signal Processing, Eag lewood Cliffs, New J e r s e y : P ren t i ce Hall, 1975.
[ 15 ] FANG, H.Y. and KROENER, R.M. Soi l s t ruc ture in te rac t ion dur ing b las t ing. International Symposium on Soil Structure Interaction, University of Roo rkee , India, 1977
[16 ] DIN 4150/3, Erschütterungen im Bauwesen; Einwirkungen auf bauliche Anlagen (Vibrat ions in building; effects on s t ruc tu re s ) .
[ 17 ] CROCKETT, J.H.A Piling v ib ra t ions and s t ruct u r e s failure. Recent Development in the DeSign and Construction of Piles, Institution of Civil Eng i n e e r s London, 1979.
[ 18 ] GASCH, Eignung de r S c hw i n g u n g sme s s u n g zur Ermit t lung d e r d y n am i s c h en B e a n s p r u c h u n g in Bau te i l en Berichte aus der Bauforschung, 58, Wilhelm Ernst & Sohn , Berlin, 1968.
[ 19 ] DOUGLAS, B. Modal Damping De t e rm ina t i on s from R e s o n a n c e Spec t r a l S h a p e Me a s u r e men t s . Journal of the Acoustical Society of America, 58, Suppl . No. 1, 1975.
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IS 14884 : 2000 ISO 4866 : 1990
[20] PAOLILLO, A. Suitability of existing vibration criteria for rail rapid transit system. Acoustical Society of America, Atlanta, Georgia, April 21 to 25, 1960.
[21] Building Research Establishment (UK), Cracking in buildings. Digest No. 5, 1966 (reprinted 1975).
[22] ISO 3010:1988, Bases for design of structures – Seismic actions on structures.
[23] GUTOWSKI, T.G., WITTIG, I.E. and DYM, C.L. Some aspects of the ground vibration problem. Noise Control Engineering, 10, No. 3, 1978.
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