First and foremost, my thoughts and prayers are with the people of Japan.
Japan is no stranger to earthquakes, but the last incident was nothing like the country had ever seen before. Registering at a record breaking magnitude 8.9, the earthquake even triggered a staggering 10 m tsunami which swept away boats, cars, homes and people as widespread fires burned out of control. While there is no question that the devastation has been massive – the situation could have been worse. Given the country’s past experience with these life-threatening tremors, Japan boasts one of the most well-thought out building codes in the world. With a system that underscores the importance of smart design and preventative measures, millions of lives may very well have been spared.
Huge shock absorbers, walls that slide and Teflon foundation pads that isolate buildings from the ground all help explain why medium- and high-rise structures in Japan remained standing in the wake of the country's largest earthquake on record. The location of the earthquake might also explain why most of the structural damage reported appears to be from the tsunami that followed the quake rather than the shaking itself.
Since the devastating Kobe temblor in 1995, Japan has become a world leader in engineering new structures and retrofitting old ones to withstand violent shaking. The Japanese are at the forefront of seismic technology, all modern structures have been designed for earthquakes and strong Japanese building codes specify rules for short, medium and tall buildings.
New buildings shorter than three stories are required to have reinforced walls and foundation slabs of a certain thickness, meaning there is not a whole lot of design to it.
Mid-rise buildings, those up to 30 m, require much more-intensive engineering, while designs for high-rise structures often employ innovative earthquake-resistant designs that undergo rigorous review by the country's top structural engineers.
The omnipresent threat of large quakes has turned shake-proof innovations into selling points for new high-rises, drawing higher rents.
Mid-rise buildings such as hospitals and laboratories in Japan, as well as on the West Coast of the United States, often rest on huge rubber or fluid-filled shock absorbers. While the shocks in a car bounce up and down, these larger absorbers slide side to side, quickly dissipating lateral motion and turning it into heat. In other words, they allow quite a bit of movement. Other shorter and mid-rise buildings rest on Teflon-coated pegs embedded in the foundation. The weight of the structure anchors the building on the pegs, but when the ground shifts the entire building slides over the smooth surfaces. This technique is one of many "base isolation" methods that decouple buildings from the ground beneath, rendering them subtly floating structures.
Taller buildings employ more sophisticated measures, often in combination. All modern skyscrapers are engineered to be strong yet flexible, so they sway in the wind - a discomfiting sensation felt on the observation decks of super-tall buildings. So, designing extra flexibility into the tallest buildings is essential for earthquake-proofing.
Video filmed during the aftershocks that hit Tokyo shows high-rises doing exactly that - wavering dramatically without snapping.
Hollow walls hiding sliding metal plates are also common in recently built mid- and high-rise buildings in Japan. The heavy plates help dissipate motion. The most sophisticated systems employ fluid-filled shock absorbers that slosh thick oil in the opposite direction of any swaying. One of the tallest buildings in Tokyo, the 238 m Roppongi Hills Mori Tower, included such a "semi-active oil damper" design when completed in 2003.
Although the high-rises of Japan may be in good shape, I worry that traditionally built houses fared much worse. My strong feeling is that there are collapsed wooden buildings in the hills and rural areas over there that we don't know about yet.
Too many people died in wood-and-tile homes during the Kobe earthquake and that toll prompted the Japanese government to launch an intensive research and retrofitting program - called "Dai-Dai-Toku," or, roughly translated, "very, very special" - to prevent a similar catastrophe.
It remains unclear how those efforts performed these days, but it will be found out soon. I usually believe that we learn engineering the "morning" after the earthquake and I reckon that this promises further improvement on earthquake-resistant construction, from now on in terms of multi-hazard approach!
Best wishes,
Efi
