8/9/2019 Japanska Kontrola Konstr Izolacija HibridAktiv

1/3

April 2010 7

COVER STORY

T he mainstream ap-proach to buildingearthquake-resistantstructures had been tomake them strongeragainst seismic shocks.

But even when such buildings arecapable of surviving violent quakeswithout collapsing, this has not re-duced secondary damage, such aspeople being injured by falling fur-niture and other items. Researchershave thus since been focusing ontechnologies to absorb the energyof seismic events, namely, base iso-lation and vibration damping.

Seismic Rubber Bearings

Base isolation involves inserting

seismic isolation devices betweenthe foundation and main body of astructure to reduce the seismic en-ergy that reaches the building it-self. The most effective substancefound for this purpose are seismicrubber bearings. The leader intheir technological development,with over 50% of the domesticmarket, is global tire maker Bridge-stone.

Since the Kobe quake, use ofseismic rubber bearings has spreadfrom emergency facilities like hos-pitals and fire stations to multiunitresidences, historical buildings,and high-tech factories, notes No-buo Murota, manager for seismicisolation products and engineeringdevelopment at Bridgestone. To

meet such diversifying needs,weve developed varying types andsizes of seismic rubber bearingproducts.

At present, around 2,500 build-ings in Japan have been built withsuch a shock-absorbing layer.Bridgestones seismic rubber bear-ings are currently being used in arestoration project for the historicmain concourse of Tokyo Station.

The base-isolation technology

developed in Japanland of fre-quent earthquakesis now beingapplied around the world. Bridges-tones seismic rubber bearings are

Japans Latest Earthquake-Resistance Technology

When the Great Hanshin Earthquake hit Kobe in January 1995, 83.3% of fatalities were caused bycollapsing buildings. The lessons learned from the tragedy have spurred the evolution of seismic-resistance technology in the years since then.Japan Echo introduces some of Japans world-leadingantiseismic technologies.

Traditional Structure Structure with Base-IsolationTechnology

Seismic Rubber Bearings

Swaysviolently

Swaysgentlyin parallelmotion

Bridgestone

Nobuo Murota Bridgestone

8/9/2019 Japanska Kontrola Konstr Izolacija HibridAktiv

2/3

Highlighting JAPAN through articles8

COVER STORY

used in important buildings on theWest Coast of the United States, aregion similarly prone to earth-quakes, including Los Angeles CityHall, the communications dispatchcenter of the Los Angeles PoliceDepartment, and Pixar AnimationStudios.

Interest has increased in re-cent years owing to the spate of violent earthquakes around theworld, Murota says. In 2009 I wasinvited to give a talk on seismicrubber bearings in Indonesia. Re-searchers from all over the worldwere there, and I was surprised bythe level of interest in the technol-ogy. Indonesian researchers wereparticularly enthusiastic, as thecountry is not only highly prone toearthquakes but is also a majorproducer of natural rubber.

Pagoda in the Sky

Vibration damping, meanwhile,relies on antisway devices posi-tioned inside the building itself toabsorb seismic shock. This makesthe technology effective againstnot only earthquakes but alsostrong gusts. Tokyo Sky Tree is adigital terrestrial broadcast towerbeing built in Sumida Ward to re-duce the impact of the increasing

number of high-rise buildings inTokyo. As of March 2010, thestructure was more than 300 me-ters high; when operations beginin spring 2012 it will be the tallestfree-standing broadcast tower inthe world, at a height of 634 me-ters. The antiseismic technologiesused in the structure are a ground-breaking fusion of traditional tech-niques and the very latest moderntechnology.

The tower is a two-part struc-ture comprising an outer steelframe and a cylindrical inner shaftmade of reinforced concrete. Thepoint to note is that the two ele-ments are independent of one an-other; if the two pieces were tightlyfixed together, this would amplifythe sway of an earthquake. Becausethe frame and shaft move sepa-rately, their seismic energies canceleach other out, reducing theamount of energy brought to bearon the tower by as much as 40%.

This vibration-damping tech-nology incorporated in the centralshaft was inspired by Japans an-cient Buddhist structures, such asfive-story pagodas. Such pagodashave an independent central shaft,which is thought to play a signifi-cant role in making the structureresistant to earthquakes. As far as

records show, none of these pago-dasincluding that at the templeHoryu-ji in Nara built 1,300 yearsagohas ever been toppled by anearthquake; something in theirstructure is thought to make themresilient to seismic disturbances.

To further make the Sky Treeresistant to collapse, the pilings ofthe foundation are not straightpoles but walls of concrete rein-forced with spike-like protuber-ances to increase their frictional

resistance. These protuberancesact like the spikes on sports shoesand help reduce the pressure thatmight otherwise cause the building

By alternately stacking layers of thin rubber discs and steel plates, Bridgestones seismic rub-ber bearings can support weight 1,000 times greater than rubber alone and can stretch 400%horizontally. It can thus reduce the shock of an earthquake measuring 7 on the Japaneseseismic intensity scale to an equivalent of a quake registering 3. Bridgestone

375m

634m

125m

Nikken Sekkei

Inner shaft

Secondobservation

deck

The inner shaft andouter steel frame areconnected with anoil damper.

The inner shaftand outer steelframe are fixedto one another.

o yo y ree s rat on- amp ngTechnology

Firstobservation

deck

8/9/2019 Japanska Kontrola Konstr Izolacija HibridAktiv

3/3

April 2010 9

COVER STORY

to collapse. These pilings aredriven 50 meters into the groundand then fan out radially like theroots of a tree to bind themstrongly to the surrounding earth.

The tower is set to open inspring 2012 with two observationdecks at heights of 350 m and 450m, along with shops, restaurants,and offices in an adjacent complex,and it is expected to become a newsymbol of Tokyo.

The Worlds Only EarthquakeSimulator

In the past, earthquake engineer-ing researchers carried out labora-tory tests on reduced-scale modelsor selected components of a struc-ture, such as a wall or column, saysTakahito Inoue, the Planning Sec-tion chief of the Hyogo EarthquakeEngineering Research Center.

Such tests have been used asbaseline data for seismic designstandards. However, the 1995 KobeEarthquake destroyed many struc-tures that were believed to be suf-ficiently earthquake resistant.

Our facility, known as E-De-fense, was established in 2005 inresponse to that disaster. E-De-fense operates the worlds largestindeed the only earthquake sim-ulator that can shake full-scalestructures. We test real structuresto understand how structures ac-tually fail and collapse during anearthquake and to evaluate the ef-fectiveness of seismic-upgrademethods.

At E-Defense, we examinewhat earthquakes do to structures.We examine how damage occursduring an earthquake, how far thedamage extends, and how thedamage eventually leads to failure

of a structure, claims Inoue.The test bay has an area of5,200 square meters and height of43 meters. It houses a 20-meter

long and 15-meter wide table thatcan shake buildings weighing up to1,200 tonsequivalent to a six-story reinforced concrete building.

The shake table has five hy-draulic actuators positioned alongthe x-axis, five along the y-axis,and 14 along the z-axis. Each ac-tuator exerts a thrust of up to 450tons. The shake table can repro-duce extreme three-dimensionalearthquake ground motions, suchas long-period, long-duration mo-tions, and recorded motions fromthe Kobe quake amplified by a fac-tor of 1.3.

The majority of buildingsdamaged in Kobe were constructedbefore an important change wasmade to the Japanese seismic de-sign standards in 1981, notesInoue. The collapse of the ele- vated highways was completelyunexpected. Structures similar tothose destroyed in Kobe existthroughout Japan, and the thoughtof experiencing the same loss and

disruption is daunting. So one ofthe immediate roles expected of theE-Defense facility was to confirmthe effectiveness of seismic upgrade

operations adopted nationwide.In the very first test, we sub-

jected two wooden houses simul-taneously to a simulated Kobequake and demonstrated how up-grades may improve seismic per-formance. Subsequently, we exam-ined various structures built in the1970s, from reinforced concretebuildings and steel buildings toconcrete bridge piers. The testshave advanced our understandingof the real seismic behavior ofstructures and established the ef-fectiveness of seismic upgrademethods implemented since theKobe quake.

We are also interested in in-ternational collaboration. For ex-ample, we have conducted jointprojects on steel buildings andconcrete bridge structures with theNetwork for Earthquake Engineer-ing Simulation program of theUnited States. I also want to em-phasize that our experiments areopen to the public. Watching a real

building collapse during an earth-quake is an extremely educationalexperience to heighten ones aware-ness of the need to be prepared.

The large shake table of the E-Defense test facility enables researchers to check the effectivenessof seismic upgrade measures using life-size residences and other large structures. E-Defense