INTERNATIONAL COOPERATION

Measuring QuakeResistance in Buildings
In last month’s column introducing initiatives of Japan’s Building
Research Institute, we looked at the Institute’s work to improve thefire-resistance performance of buildings. In this month’s issue, we turnto the Institute’s research into strong motion observation andmeasurement of the structural safety of buildings.

T

he problem of building
structures capable of withstanding earthquakes is one
that Japan confronts perennially, given that it is highly prone tosuffering earthquakes. The first step toensuring structural earthquake resistance is understanding earthquake
ground motion and the effect this phenomenon has on buildings.
The Fukui Earthquake of 1948
caused more than 3,700 fatalities anddestroyed more than 36,000 residences.
There was no way of knowing what theearthquake ground motion at the site waslike, however, nor how the buildings
there were shaken so as to cause theirdestruction. While it is true there were, infact, seismographs around at that time,

89 m

34.5 msuch instruments as did exist were intended to measure only minute tremors;they were incapable of recording tremorsof intensity sufficient to result in damage,as such violent shakes exceeded the design tolerances of these devices.
Lessons learned from the experienceof the Fukui Earthquake gave rise to arenewed awareness of the need to reliably record large earthquake shakes,
which led to the development of strong
motion instruments for the purpose.
Strong motion observation accordingly
commenced in Japan in the 1950s, withthe aim of reliably and accurately
measuring structural vibrations that arisein the ground, as well as buildings andother structures, when major earthquakes
occur. Particular emphasis was laid
upon strong
motion obser8FE
8FN
8FS: Acceleration sensor
vation concerning buildings,
5FW
5FE
owing to thedirect threat
2FW
2FE
20 m
50 m
100 m
that damage to
1FE
A01
B01
C01
these structuresposes to their
BFN
BFE BFS
A14
occupants.
N14
Aggressive efforts were accordingly madeby the now forA43
mer Japanese
Ministry ofConstruction,
among otherorganizations,to install
strong motion
seismographs
A89
in buildings.
Figure 1: Observation taken by placing a plurality of seismic
Carrying
sensors both in a building and the surrounding ground. Thisout strong
observation used the portion of the Building Researchmotion obserInstitute’s Strong Motion Observation Network with thevations whenhighest density of sensors in place.
12

the first skyscrapers were built in Japanin the 1960s led to verifications of analytical techniques and methods of design,and the fruits of these efforts have been
put to good use in construction since thattime. Technologies such as Seismic
Isolation and Seismic Response Control,
which first came into practical use in the
1980s, were also verified for performanceby means of strong motion observation.
They have rapidly proliferated since theirinitial adoption for their efficacy in improving structural quake resistance. In
this fashion, strong motion observationof buildings has played a crucial part in
the evolution of seismic technology.
A strong motion seismograph is a
device that measures vibrations in the
ground and buildings when an earthquake
happens. Strong motion seismographs
are typically made to measure vibrations
traveling east to west, north to south, andvertically, as well as to function reliably
regardless of how intense the shakes
affecting them may be. Such shakes may
be represented as changes in displacement, velocity, or acceleration over time.
The strong motion seismograph commonly measures acceleration.
When an earthquake occurs inJapan, a detailed Distribution of Seismic
Intensity Scale report is published withina matter of minutes. At present, theJapan Meteorological Agency (JMA)
seismic intensity scale1 is determined bycomputations derived from the strong
motion record of a given quake. Anothername for a strong motion seismographthat is specifically used in computationsof seismic intensity is a seismic intensity
meter. Together, the JMA, prefectural
governments, and the Japanese National
Research Institute for Earth Science andDisaster Prevention have distributed
more than 4,000 seismic intensity metersand strong motion seismographs, which
are used in this selfsame publication ofseismic intensity following an earthquake. These seismic intensity metersand strong motion seismographs areplanted on open ground.
Strong motion observation of buildings, by contrast, involves installing
multiple sensors in a building and making a three-dimensional recording of thevibrations that the building experiencesin an earthquake. What generally happens is as follows: a building’s founda-

Photo 1: The Niigata Earthquake of June 16, 1964, caused thefour-story buildings of Kawagishi-cho Apartments to list significantly
off center or topple altogether.

Strong Motion Observation by
Japan’s Building Research Institute

The Building Research Institute has
been conducting strong motion observation continuously for more than fifty
years. Many of the records of historicalstrong earthquakes in Japan, such as therecords from the prefectural-run housing
in the Niigata Earthquake of 1964 or
the records from Tohoku University of
the Off Miyagi Prefecture Earthquake
in 1978, have been obtained by the
Building Research Institute’s Strong
Motion Observation Network. The
aforementioned Niigata Earthquake,
which happened on June 16, 1964,

NAKA

tion is shaken by an earthquake, the oscillations of the foundation are amplified
throughout the building, and the uppermost portion of the building shakes
widely. The ways that buildings shakevary depending on the building’s structure and shape, and as a consequence,the placement of seismic sensors isplanned in accordance with the characteristics of any given building. Figure 1
depicts an example of an observation
taken by placing a plurality of seismic
sensors both in a building and the surrounding ground. The example shown
involves the portion of the Japanese
Building Research Institute’s Strong
Motion Observation Network with thehighest density of sensors in place. With
that caveat in mind, observing shaking
on the part of a building in an earthquake requires that seismic sensors be
installed in the foundation and at the topof that building at a minimum.

ORID
THU
SND
MIYA
TRMA
TAMA

THE NIIGATA NIPPO

caused tremendous amounts useful in verifying the philosophy ando f d a m a g e c e n t e r e d o n techniques that were applied to quake
Niigata Prefecture, on the resistance at the time. The strong motion
S e a o f J a p a n c o a s t o f records of the observations that wereHonshu, Japan’s main is- taken on the first floor of the building
land. The Kawagishi-cho were used as the input seismic motion
Apartments, which were for building quake resistance designs.
o p erated by the Niigata
As of this writing, the Building
Prefectural Government, Research Institute’s strong motion obsersustained severe damage, vation involves 214 seismic sensors
when its four-story buildings located in 76 sites across Japan, making
listed significantly off center it the preeminent firm working in strong
or toppled altogether ( photo 1 ). The motion observation of buildings in the
Building Research Institute’s strong mo- country. Figure 2 depicts the locations oftion seismographs were installed in one the Institute’s observation sites. Of these,of the buildings that listed to a degree one-third are located in the metropolitan
off center, and the records obtained from region centering on Tokyo, with the rest
those strong motion seismographs pro- distributed so as to provide nationwide
vided the first strong motion record of a coverage, primarily focused on major
regional cities. The Institute has madedamaging earthquake in Japan.
The resulting strong motion record improvements to the organization of its
clearly indicated that the ground lique- systems and to its devices since it comfied during the quake, revealing that the menced observations, and is installing thelisting and toppling of buildings during very latest in digital strong motion seisthe quake was due to the Liquefaction2 mographs at all of their observation sitesof the ground on which they stood. As as of this writing. Almost all of thefor the Off Miyagi Prefecture Earthquake Institute’s strong motion seismographs
in 1978, records were obtained from are connected to the Building Research
the strong motion seismographs that were
installed in the
Kanto Area
first and ninth
SapporoTsukuba Mt.
TsukubaMiyashiro
floors of a nineAgeo
KushiroMitsukaido
Noda
story building
Hiroo
Toda
MisatoHakodate
Yachiyoon the Tohoku
Kodaira
Chiba
University camHirosaki
KawasakiHachinohe
Yokohama
pus. The maxiMiyako
kmAkita
mum accelera0
20 40
Tsuruokation readings
Niigataobtained from
Joetsuthe strong moIwaki
SendaiKanazawa
Naganotion records from
Maizuru
Kiso
YonagoKofu
the strong motion
HamadaNagoyaOsaka
seismographs
Hiroshima
ShimodaTakamatsu
Fukuokakm
that were inMatsusaka Shimizu
0
10
20
Oita
Shingustalled on the
Kochi
ninth floor of
Nobeoka
Miyazaki
the building inkm
Miyakonojo
question exceed0200400
ed one g 3 , andthe resulting
Figure 2: Locations of the Building Research Institute’s
observation sites
records were13

INTERNATIONAL COOPERATION
away from the building, owing to thebasement being affected by the building
itself. Collection and analysis of casehistories of observations of a variety ofground surfaces and buildings facilitatesaccurate assessment of input seismic
motion, leading to improvements inquake resistance technologies.
THE HOKKAIDO SHIMBUN PRESS

Long-period Earthquake Motion
and Responding with Long-period
Buildings

Photo 2: An earthquake off the Pacific Coast of Hokkaido in 2003 caused
oil storage tanks to catch fire at a refinery in Tomakomai, over 200 km
from the epicenter, when the naphtha and petroleum in the tanks shook insynchronization with the slow moving tremors.

Institute by telephone lines, allowing
reduced complexity in maintenance andrapid collection of data records.
Ascertaining of Input Seismic
Motion as Applied to Buildings

tion observation of the building is anefficacious means of accurately assessing such phenomena and elucidating
what sort of effect they have on theseismic response of the building. An
example is depicted in figure 3. The
graph shown on the right hand side ofthis figure compares the intensity of thestrong motion records obtained to-datefrom the basement (B1 floor) of a tenstory government building in the city ofHachinohe and the ground level (GL)nearby at respective maximum acceleration values. The maximum accelerationin the basement (B1) is as much as halfor less that of the surface of the groundLong-period earthquake motion 4 , inwhich long, slow shakes occur, has
drawn people’s attention in recent years.
The motivation for such interest lies in
the Off Tokachi Earthquake on the
Pacific Coast of Hokkaido, in 2003. As
a result of this earthquake, oil storage
tanks caught fire at a refinery located in
the city of Tomakomai, over 200 km(125 miles) from the epicenter (photo2). The fire was caused by a sloshing effect, wherein the naphtha and petroleum
in the tanks experienced great shaking in
synchronization with the slow moving
waves that were emitted by the earthquake. The quake intensity registered atTomakomai was 5-, which would normally not have been a strong enoughlevel to cause damage. At times, longperiod earthquake motion may cause
unimaginable catastrophe, and have asignificant effect on the vibrations thatbuildings suffer as well.
Skyscrapers first appeared on theJapanese landscape in the 1960s, andPeak Acc. at Base (cm/s2)

Following the Kobe Earthquake of
1995, the JMA and other organizations
assembled a large-scale Seismic
Intensity Network, which has accumulated many data records concerning
tremors, or seismic vibrations, happening in the ground when major earthquakes occur, and consequently allowed
the obtainment of a variety of kinds ofknowledge about the subject.
At the same time, analyses of1000
the resulting tremendous volume
Peak acceleration
10Fof data have led to the discovery
500
that the seismic vibrations thatare observed in the ground do200
not act directly on buildings
100
standing on that ground. The
50
input seismic motion that acts
on buildings is altered by the20very presence of the buildings
ABase = 0.42 AGL
themselves, rather than simply
10
ABase = 0.45 AGL
the conditions of the ground on
5GLwhich the buildings stand. The
X
01F
Y
alterations in question are comB1F
2plicated and very difficult to as2
5 10 2050 100 200 500 1000
sess, as they are influenced by
Peak Acc. on GL (cm/s2)
the scale and embedding of the
Figure 3: The graph on the right compares the intensity of the strong motion records obbuilding, as well as the form oftained to-date from the basement (B1 floor) of a ten-story government building in the city
the foundation. The strong moof Hachinohe and the ground level (GL) nearby at respective maximum acceleration values.
14

tion was amplified between six and ninetimes at the top of the building, and thevibrations went on at that part of thestructure for five minutes or more.
Given that the typical earthquake duration is on the order of one to two min-Acc. (cm/s2)

Acc. (cm/s2)

base-isolated buildings came into general use in the 1980s. Many skyscrapers
and base-isolated buildings are being
built in metropolitan areas across Japanas of this writing. At the same time,
there are also many examples of50

37F(NS) (peak:- 29.8 cm/s2)

0
-50
50

37F(EW) (peak: 50.9 cm/s2)

0-50

Acc. (cm/s2)

Acc. (cm/s2)

0

50

100

150
Time (sec)

200

50

250

300

01F(NS) (peak:- 5.0 cm/s2)

0
-50
50

01F(EW) (peak:- 5.8 cm/s2)

0
-50
0

50

100

150
Time (sec)

200

250

300

Figure 4: Strong motion record of the first and thirty-seventh floors of a thirtyseven-story apartment building built of reinforced concrete in the Tokyo Bay
area following the Chuetsu Offshore Earthquake of July 16, 2007.

Japanese cities making expansions intolarge plains areas. The soft, flexible,
thick sedimentary layers and geographical features of the ground on whichthese cities stand cause a significant riskof amplification of long-period earthquake motion. Skyscrapers and baseisolated buildings are both characterizedby having a long natural period5, whichleads to a risk that they will resonate
with long-period earthquake motion thatwould be amplified by large plains, resulting in the buildings being assaulted
by vibrations beyond imagination. It isthus crucial to employ the latest knowledge and technology to accurately envision what would happen should a major
earthquake strike at some future time.
Figure 4 shows a strong motion
record of the first and thirty-seventh
floors of a thirty-seven-story apartmentbuilding built of reinforced concrete in
the Tokyo Bay area that was obtainedon the occasion of an earthquake that
occurred in the Sea of Japan off thecoast of the Chuetsu region of Niigata
in 2007. Whereas the first floor of thebuilding experienced quake vibrations
on the order of five gals6, a small degreeof acceleration, this selfsame accelera-utes, these results mean that the top of
this building shook for as much as threetimes as long. The facts are that major
Japanese cities such as Tokyo have notexperienced major quake vibrations
since the commencement of strong motion observation, and old models ofstrong motion seismographs lacked thecapability to capture strong motion records that vibrate long and slowly, andwith a small amplitude. High performance strong motion seismographs
have been assembled in recent years,
however, and have been shedding lighton phenomena such as these. The
Chuetsu Earthquake of 2007 registereda magnitude 6.8 on the Richter Scale,and the future great earthquake thatpeople fear is envisioned to be magnitude 8.0 or greater. Measures are thus
necessary that take into account thelikelihood of having to respond toquakes of much longer duration andgreater amplitude.
It has been more than half a century
since Japan commenced strong motion
observation. In that time, the fruits ofsuch strong motion observation haveplayed a significant role in improving
technologies for designing quake resis-

tance into buildings. The number of observation sites on the ground increasedd r amatically f o llo w in g the K o b eEarthquake of 1995, due to the assemblyof a seismic intensity observation network. The number of observation sites
and records on buildings is still far from
adequate for the task, however.
Many issues yet remain for whichfurther research and development efforts
are needed, including more precise assessments of input seismic motion andmore accurate determinations of thestructural soundness of buildings. At the
Building Research Institute, we intend
to contribute to building both stronger
buildings and a stronger community byundertaking sustained research anddevelopment efforts related to the strong
motion observation of buildings, while
we promote the further proliferation ofjust such observation.
Notes:
1. Japan uses its own unique seismic intensity scale, which is divided into 10
levels as follows: 0, 1, 2, 3, 4, 5-, 5+, 6-,
6+, and 7.
2. A phenomenon in which the groundloses its rigidity, and takes on the properties of a liquid, as a result of intense
earthquake shaking.
3. The acceleration of an object in Earthgravity in free fall: 980 cm/s2, or 32 ft./s2.
Quake resistance designs for buildings
at the time were predicated on withstanding earthquakes on the order of
one-g acceleration.
4. A “period” refers to the time required
for a tremor to complete one cycle.
“Long-period earthquake motion” refers
to a seismic vibration wherein a single
period lasts between several seconds andup to 20 seconds.
5. Buildings have natural periods, whichrefer to the periods at which they are
most likely to shake. A building’s natural period is affected by such factors as
its shape, size and structural form.
6. gal, short for Galileo Unit, is a unit ofacceleration, defined as one gal being
equal to one cm/s2, such that Earth gravity, one g, is equal to 980 gal.
15