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Journal Article•DOI•

Determination of the natural periods of buildings

R. Crawford1, H. S. Ward1•
National Research Council1
01 Dec 1964-Bulletin of the Seismological Society of America (GeoScienceWorld)-Vol. 54, pp 1743-1756
TL;DR: In this article, the first three modes of vibration of a nineteen-story building about the two major translational axes and the torsional axis of the building were determined by random wind excitation.
Abstract: Random wind excitation has been used to find the first three modes of vibration of a nineteenstory building about the two major translational axes and the torsional axis of the building. Vibration records were obtained with Willmore electromagnetic seismometers feeding into a multichannel magnetic tape recorder. A harmonic analysis was then performed with the aid of an analogue computer to determine the first few vibration modes. Concurrently with the experimental program the building modes were computed two ways using different simplifying assumptions regarding the lateral stiffness of the structure.

Summary (1 min read)

Jump to: [I] – [Fi.an~e Action Onlg] and [/ i'requency cps]

I

  • Siniultaneous recordings were obtaiiicd at floor levels 1.5, 11, 7, aiid 3 with the transducers at location 3 (fig. 2 ) ~vhen the cxciting forcc was a light niiid.
  • L'arts of the calibrated power spectral dciisity curvcs for the vibi~atioiis parallel to thc short dinleiision arc sllonril in fig.
  • This givcs a nicasurc of thc lU1S displacciilcnt of thc vibration on cacall flooi.
  • The calculation of the natural pcriods of vibration of this building is a complicated problcni becausc it coiilbiiics two distinct typcs of construction: a rcinforccd corirrctc core incorporated within a stccl-fraiilc structurc.
  • For the first sct of calculatioiis the follo~ving assunlptioiis wcre also madc.

Fi.an~e Action Onlg

  • Thc closest agrccnlerit with thc experimental ~vork is in the fu~idalllelital ~ilode parallcl to the short dilnension of the building.
  • The calculated value for this pcriod is 1', = 1.39 sec n~hich colnpares favourably with the observed period To = 1.28 sec.
  • The othcr calculated inodes are higher thau thc corrcsponding obscrvcd lllodes by a factor of almost 2.
  • If tllc nlalls do contributc to the shear stifflless then, according to thcir geometric shapcs, the building would be stilrcr in thc long di~llensioii than ill the short dimension.

/ i'requency cps

  • Substituting the values for thc Satiorlal Health and Welfare Building in this forinula givcs pcriods of 1.25 scr parallcl to the short dirllcllsio~l arid 0.99 sec parallel to the lorig dinle~lsiorls.
  • With the advc~lt of inoderrl rccordiilg ancl ailalysis ccluip~ueilt the state of the art has been g~.catly adva~ic*cd.
  • Illearl ~vi~ld velocity i~lc~*eases, the broad spectral peali of wind cricigy tcl~ids to illovc froin very loiig periods to~vards shorter periocls.
  • For light \\rinds the various riatural periods of the buildirig lie or1 a flat part of the spectral ericrgy curve, rcsulti~~g in siiililal cxcitatioii of liiaily illocles.
  • As the ~vinds ir~crcase in strcilgth the broad spcc.t~.al peak illovcs upnrard to~t~aid the furida~l~crital natural periods of the building, ~vllich coiisecluc~ltly arc. excited nlorc.

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Bulletin of the Seismological Society of America, 54, 6, pp. 1743-1756, 1964-12
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Determination of the natural periods of buildings
Crawford, R.; Ward, H. S.
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AN
AgJyzED
Bulletin of the Seismological Society of America. Vol. 54, No. 6,
pp.
1743-1756.
December, 1964
DlrIIIIl'IO
01:
THE KAVl'UltAIJ I'EItIODS
01;
I3UII,DIS(;S
131-
R. Cna'i~n-oar)
am
I-I.
S. WAI~I)
1t:rndorn wind
excitation
lias been used to firltl thc first three
nodes
of vibration of
a
niilctcc~l-
st80ry 1)uiltling allout thc l,mo
major
transl:~tio~l:rI
~LSCS
and thc torsional axis
of
the I~uilding.
\'il~ration rccords werc obtained wit11 Willmore clcctrolnagnctic seismomct,crs fcecli~lg into
a
~nr~ltiohanncl ~rl:rgnctic tspc
recorder.
A
h:rrmonic r~nalysis
was
then
performed n.it.li thc :Lid
of a11 nn:~logue co~npul,cr
to
tlet,errni~ic thc first fc~ vil)r:~tion modes. Cot~crirrcntly wit11 the
esperi~netrt:~l progruln t,hc building
modes
were cornputcd t,\vo ways using different. si~uplifying
:rssuu~ptions regarding thc lnt,cral stiif~~css of tllc
structure.
This study was prompted by the liced for accurate informatio~~
011
the.
~~atural
pcriods of vibratioii of buildings for cotnparisoii with valucs predicted froill iiiatllc-
t~iatical modcls. Studies of this type wcrc initiated soiile ycars ago by tllc
U.
S.
Coast and Gcodctic survey but it was bclicved that inorc accuratc and extclisivc
inforination about wind-excited structures could be gained using modcrii iiirthods
of analysis. Accordingly, a trial prograin was undcrtalie~i oil one buildi~~g.
The building was a new Fcdcral Governiilcnt building, built for thc Depart~~iciit
of Public Works to house thc Dcpartincilt of Natiorial Health and Wclfare, located
at Tuniicy's Pasture in Otta'i'ira. Tlle buildii~g itsclf is situated on an csposccl parli-
lalid arca with vcry few trees or buildings nearby. Conlprisirig 19 storics (17 floors,
ground level arid basement) and shapcd like a rccta~~gular prisin, it is
140
by
88
ft
by
23.5
ft
high. The structural steel columns of the building run thc full hcigllt with
the iliaill structural changes occurrilig at thc 4th arid 14th floors. In tllc c*clitcr of
the structure is a stccl aiid coilcrcte core that llouscs thc elevator sliafts aiid stair-
ways. Of ii1oi.e iilassivc coiistructioi~ tlia~i
no st
modcrn office blocks, the 1)uilding
has 11-ill. rcinforc-ed concrctc floor slabs arid outsidc walls coiliposccl of Iic~~vy
precast co~icrctc wirido\\r scctio~~s, each wcighirig approxiinatcly 2 tons. The weight
of tllesc window sections at each floor level is horne by the floor slab itsclf so that
the outsidc walls are not cao~~sidercd as a siriglc structural uiiit. Figurc
1
shows a
general
view of thc buildi~~g; figure 2 indicates thc layout of thr struct~ur.
The Ileait of ally ~ilcasuri~ig systenl is tlic serisii~g clnilellt. Siiicc tlic pcriods of
vibration of sti~ucturcs that are of iiitcrcst lie in the same rangc as tllosc pcriods
obscrvcd in eartliclualics, gciierally in thc range
0.05
to
10
secoiids, it \\-as obvious
that a traiisduccr such as is uscd for 1-ccordi~~g carthc~uakcs could bc uscd to record
structural vibrations. Not
only is it sciisitivc ill thc correct freclucncy rangc, but
becausc of its high scilsitivity
it
is idcal for i.ccording sillall liiotioi~s of buildi~lgs
induccd by 1vi11d escitatioii.
The Willniore JIarli
I1
scisinonlctcr was uscd in this study. This is ail clectro-
inagnctic
transducer
with a fixed (.oil aiid a heavy irlagilct that acts as thc niovirig
nlass. It (*an bc set to ineasurc in either th~ vertical or horizoi~tal direction. Thc
Citations
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Marc Wathelet1, Jean-Luc Chatelain1, Cécile Cornou1, Giuseppe Di Giulio2, Bertrand Guillier1, Matthias Ohrnberger3, Alexandros Savvaidis4 •
University of Savoy1, National Institute of Geophysics and Volcanology2, University of Potsdam3, University of Texas at Austin4
01 May 2020-Seismological Research Letters
TL;DR: Geopsy has become a mature multiplatform open-source package that has already been recognized as a reference tool for analyzing ambient vibration data in the context of site characterization studies and a number of lower-level tools guarantee maximum flexibility in accessing and controlling processing results at any stage of the analysis.
Abstract: Ambient vibrations are nowadays considerably used worldwide for numerous types of engineering applications and scientific research. Geopsy and its companion tools are part of that landscape. Since the first release of the program package in 2005, as outcome of the European Union project Site Effects aSsessment from AMbient noisE, Geopsy has become a mature multiplatform open-source package (released under GNU Public License version 3) that has already been recognized as a reference tool for analyzing ambient vibration data in the context of site characterization studies. The community of users has grown from a core group of researchers up to thousands of seismologists and engineers on every career level and on all continents. The versatility of geopsy allows for the processing of all kinds of data needed in site characterization studies, that is, from single station single trace to three-component array recordings. In all of the aforementioned cases, the steps from field acquisition to the production of publication-ready figures are covered and supported by user-friendly graphical user interfaces or corresponding command-line tools for the automation of the complete processing chain. To avoid black-box usage, a number of lower-level tools guarantee maximum flexibility in accessing and controlling processing results at any stage of the analysis.

177 citations

Journal Article•DOI•
Comparisons between ambient and forced vibration experiments

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Mihailo D. Trifunac1, Mihailo D. Trifunac2•
Columbia University1, California Institute of Technology2
01 Jan 1972-Earthquake Engineering & Structural Dynamics
TL;DR: In this article, the authors compared the effect of unwanted modes on the response near resonance of the mode being sought and showed that the mode amplitudes determined by ambient and forced vibration tests show systematic departure for high modes and near the top levels of buildings tested.
Abstract: The ambient and forced vibration techniques for testing full-scale structures are critically compared. Both methods, based on small level excitation, may be used to determine many mode shapes and frequencies of vibration and the corresponding damping values, with adequate accuracy for most purposes. The two techniques give mutually consistent results. The mode amplitudes determined by ambient and forced vibration tests show systematic departure for high modes and near the top levels of buildings tested. This phenomenon is attributed to the participation of all mode shapes and is a consequence of excitation by a concentrated force near the top of a building and at a frequency differing by only a few per cent from a natural frequency of vibrations. A new way of showing the effect of unwanted modes on the response near resonance of the mode being sought is developed. It is particularly useful for the analysis of steady, forced vibration tests of structures using eccentric mass vibration generators.

169 citations

Journal Article•DOI•
Recent perspectives in dynamic testing and monitoring of bridges

[...]

Álvaro Cunha1, Elsa Caetano1, Filipe Magalhães1, Carlos Moutinho1•
University of Porto1
01 Jun 2013-Structural Control & Health Monitoring
TL;DR: In this article, the authors reviewed some of the most recent aspects involved in the dynamic testing and continuous monitoring of bridges, including testing techniques, instrumentation, modal identification and damage detection.
Abstract: SUMMARY The paper reviews some of the most recent aspects involved in the dynamic testing and continuous monitoring of bridges. This includes a discussion of testing techniques, instrumentation, modal identification and damage detection. On the basis of their experience, the authors described several case studies in which some of the most recent developments have been used to accomplish different purposes: the Millau Viaduct, in France, the Pedro e Ines footbridge and the Infante D. Henrique Bridge, in Portugal, and the Grande Ravine Viaduct, at the Reunion Island. Copyright © 2012 John Wiley & Sons, Ltd.

121 citations

Journal Article•DOI•
Full-scale dynamic response of an RC building under weak seismic motions using earthquake recordings, ambient vibrations and modelling

[...]

Clotaire Michel1, Philippe Guéguen2, Saber El Arem2, Jacky Mazars2, Panagiotis Kotronis2 •
École Polytechnique Fédérale de Lausanne1, Centre national de la recherche scientifique2
01 Jan 2009-Earthquake Engineering & Structural Dynamics
TL;DR: In this paper, an enhanced modal analysis technique (Frequency Domain Decomposition) was used to process ambient vibration recordings taken at the Grenoble City Hall building (France), which can contribute to the understanding of the seismic building response and the good relevancy of a modal model based on ambient vibrations for estimating the structural deformation under moderate earthquakes.
Abstract: In countries with a moderate seismic hazard, the classical methods developed for strong motion prone countries to estimate the seismic behaviour and subsequent vulnerability of existing buildings are often inadequate and not financially realistic. The main goals of this paper are to show how the modal analysis can contribute to the understanding of the seismic building response and the good relevancy of a modal model based on ambient vibrations for estimating the structural deformation under moderate earthquakes. We describe the application of an enhanced modal analysis technique (Frequency Domain Decomposition) to process ambient vibration recordings taken at the Grenoble City Hall building (France). The frequencies of ambient vibrations are compared with those of weak earthquakes recorded by the French permanent accelerometric network (RAP) that was installed to monitor the building. The frequency variations of the building under moderate earthquakes are shown to be slight (~2%) and therefore ambient vibration frequencies are relevant over the elastic domain of the building. The modal parameters extracted from ambient vibrations are then used to determine the 1D lumped-mass model in order to reproduce the inter-storey drift under weak earthquakes and to fix a 3D numerical model that could be used for strong earthquakes. The correlation coefficients between data and synthetic motion are close to 80% and 90% in horizontal directions, for the 1D and 3D modelling, respectively.

115 citations

Additional excerpts

  • ...Crawford and Ward [4] and Trifunac [5] showed that ambient vibration-based techniques were as accurate as active methods for determining vibration modes and much easier to implement for a large set of buildings....

    [...]

Journal Article•DOI•
Ambient vibration tests of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 1994 Northridge earthquake

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S.S. Ivanović1, Mihailo D. Trifunac2, E.I. Novikova, A.A. Gladkov, Maria I. Todorovska2 •
University of Montenegro1, University of Southern California2
01 Aug 2000-Soil Dynamics and Earthquake Engineering
TL;DR: In this article, two detailed ambient vibration surveys of a 7-story reinforced concrete building in Van Nuys, California, were conducted after the building was severely damaged by the 17 January 1994, Northridge earthquake (ML=5.3, epicenter 1.5 km west from the building site) and its early aftershocks.

99 citations

References
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Journal Article•DOI•
Properties of spectra of atmospheric turbulence at 100 metres

[...]

Hans A. Panofsky1, Robert A. McCormick•
Pennsylvania State University1
01 Oct 1954-Quarterly Journal of the Royal Meteorological Society
TL;DR: In this article, the properties of spectra of vertical and horizontal turbulence and of their cross-spectra, at elevations near 100m, are summarized; a few spectra from lower levels are considered.
Abstract: The properties of spectra of vertical and horizontal turbulence and of their cross-spectra, at elevations near 100m, are summarized; a few spectra from lower levels are considered. The following tentative conclusions are drawn: 1At frequencies of the order of 100c/hr and above, the spectral intensity is proportional to the square of the mean wind speed and essentially independent of the radiation intensity. At lower frequencies, the ratio of spectral intensity to the square of the wind speed increases with increasing incoming radiation. 2The intensity-ratio of the co-spectrum of vertical and horizontal velocity to the spectrum of vertical velocity increases with increasing wind shear. It also decreases with increasing frequency, n, approximately as n−1. 3At low frequencies, the spectral intensity of the horizontal velocity components is generally much large than that of the vertical velocity. At high frequencies, the spectral intensities of all velocity components are of the same order of magnitude. At low frequencies, the ratio of vertical to horizontal spectral density increases with increasing radiation. 4The quadrature spectra at a given frequency tend to be negative with large radiation, positive with little radiation. This indicates that edies are low and wide with little radiation, and tall with much radiation. 5The frequency at the maximum of the vertical velocity spectrum decreases with increasing height and increasing radiation intensity. 6The ratio of tubulent to mean energy is somewhat larger for air with over-land trajectories than for air with oceanic trajectories.

55 citations

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Modal identification of output-only systems using frequency domain decomposition

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01 Jun 2001-Smart Materials and Structures
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01 Aug 2008-Soil Dynamics and Earthquake Engineering
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In situ experiments and seismic analysis of existing buildings. Part I: experimental investigations

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